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F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
bull Empirical Formula The simplest ratio of atoms of each element present in a compound
bull Molecular formula The actual number of atoms of each element present in a compound
bull General Formula The simplest algebraic formula of a member of a homologous series eg Alkanes general formula is CnH2n+1
bull Structural Formula The minimal detail that shows the arrangement of atoms in a molecule eg for butane CH3CH2CH2CH3 or CH3(CH2)2CH3
bull Displayed Formula The relative positioning of atoms and the bonds between them ie for ethanol
bull Skeletal Formula The simplified organic formula shown by removing hydrogen atoms from alkyl chains leaving just a carbon skeleton and associated functional groups ie for butan-2-ol
OH
H
H
H
H
H
OH
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
bull Homologous series A series of organic compound shaving the same functional group but with each successive member differing by CH 2
bull Functional Group A group of atoms responsible for the characteristic reactions of a compound
Alkanes Homologous Series
Number of carbons Name Formula
1 Methane CH4
2 Ethane C2H6
3 Propane C3H8
4 Butane C4H10
5 Pentane C5H12
6 Hexane C6H14
7 Heptane C7H16
8 Octane C8H18 9 Nonane C9H20
10 Decane C10H22
bull Hydrocarbon A compound of carbon and hydrogen only
bull Saturated Hydrocarbon A hydrocarbon with single bonds only
bull Unsaturated Hydrocarbon Contains carbon-carbon multiple bonds
bull Aliphatic hydrocarbon A hydrocarbon in which the carbon atoms are joined together in unbranched or branched chains
bull Alicyclic Hydrocarbon A hydrocarbon in which the carbons are joined together in a ring structure
Carbon is in group 4 of the periodic table it has 4 electrons in the outer shell which pair up
with electrons in other atoms to form 4 covalent bonds
Alkanes re saturated hydrocarbons with single C-C bonds only Each carbon atom is bonded to
four other atoms Each carbon has a tetrahedral shape (1095)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
A
C C
H
H A
A
C C
A
H H
B
C C
A
A C
A
C C
A
C B
bull Structural Isomers Compounds with the same molecular formula but different structural formula
bull Stereoisomers Compounds with the same structural formula but with a different arrangement in space
bull EZ isomerism An example of stereoisomerism in terms of restricted rotation about a double bond and the requirement for two different groups to be attached to each carbon atom of the C=C group E Isomerism Z Isomerism
bull Cis-trans isomerism A special case of EZ isomerism in which two substituent groups are the same
CIS TRANS
oppositE
Together
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Type of Compound Formula Prefix Suffix
Alkane C-C -ane Alkene C=C -ene Halogenoalkane -F
-CL -Br -I
Fluoro- Chloro- Bromo- Iodo-
Alcohol -OH -ol Aldehyde -CHO
-al
Ketone C-CO-C
-one
Carboxylic acid -COOH
-oic acid
O
C
OH
C C C
O
O
C
H
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
During a chemical reaction bonds are broken in a process called bond fission A covalent
bond can be broken in two ways
bull Homolytic Fission
1 Each bonded atom takes one of the shared pair of electrons
2 Each atom now has an unpaired electron and is called a radical
3 Two species of the same type (lsquohomorsquolytic) are produced
X ndash Y -----gt X + Y
bull Heterolytic Fission
1 One of the bonded atoms takes both of the electrons in the shared pair
2 Two ions are produced
3 The atom that takes both electrons becomes negatively charged (anion)
4 The atom that does not take the shared electron becomes positively charged
(cation)
X ndash Y -----gt X+ + Y-
bull Nucleophile An electron pair donor
bull Electrophile An electron pair acceptor
bull Addition reaction A molecule is added across the double bond of an unsaturated molecule to make a saturated molecule
2 reactants -----gt 1 product
bull Substitution reaction An atom or group of atoms is replaced with a different atom or groups of atoms
2 reactants -----gt 2 products
bull Elimination Reaction The removal of a molecule from a saturated molecule to make a saturated molecule
1 reactant -----gt 2 products
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Percentage Yield
100 yields are rarely achieved possible causes are
bull The reaction may be at equilibrium and may not go to completion
bull Other side reactions may occur leading to by-products
bull The reactants may not be pure
bull Some of the reactants or products may be left behind in the apparatus
bull Separation and purification may result in the loss of some of the product
1313
1313
A Limiting Reagent is the substance in a chemical reaction that runs out first
Atom Economy
A reaction may produce by-products along with the desired product
What can be done with by-products
1 If it is considered to be waste by-products are disposed of This is costly and poses
potential environmental problems
2 By-products may be sold on or used elsewhere in the chemical plant This practice is
likely to increase in the future as we become increasingly concerned about
preserving the earthrsquos resources and minimising waste
Atom economy considers not only the desired product but also the by-products in a chemical
reaction It describes the efficiency of a reaction in terms of all atoms involved High atom economy
means minimal waste
1313 1313
1313
bull Addition reactions 100 atom economy
bull Substitution and Elimination reactions lt 100 atom economy
How can atom economy benefit society
By using products with higher atom economy chemical companies can reduce the amount of waste
produced which is also good for the environment since we a re running out of landfill sites It has
also been suggested that 5-10 of the expenditure of a chemical company goes on waste treatment
bull Percentage yield tells you the efficiency of converting reactants into products
bull Atom economy tells you the proportion of desired products compares with all the products
formed
bull A reaction may have a high percentage yield but a low atom economy
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Hydrocarbons from crude oil
Hydrocarbons are organic compounds containing hydrogen and carbon only
Crude oil is a fossil fuel made from naturally decaying plants and animals that once lived in ancient
seas millions of years ago It is a mixture of over 150 different hydrocarbons most of which are
unbranched Crude oil does not ignite easily so is not useful in its native state However some of its
components are valuable and are used in petrol kerosene and heating and lubricating oils
Fractional Distillation - The separation of the components of crude oil into fractions which differ in
boiling point by means of distillation
Crude oil is refined in a distillation plant
1 The mixture of hydrocarbons is separate into fractions
2 Each fraction consists of a mixture of hydrocarbons with similar boiling points
3 Pure liquids have a fixed boiling point A pure hydrocarbon can be obtained by
further distillation of a crude oil fraction
The process takes place in a fractionating column
A The crude oil is vaporised and then passed into the fractionating column The
column is hotter at the bottom than the top and the gases pass up the column
through a series of bubble caps
B Eventually the gases reach a temperature that is lower than their boiling points
Here the vapour condenses to a liquid The liquid fractions are then tapped off into
storage containers
C Short chained hydrocarbons with lower boiling points condense near the top of the
column
D Longer chained hydrocarbons with higher boiling points condense near the bottom
E Gases which do not condense pass through the top of the column as lsquopetroleum gasrsquo
F The residue from the process is bitumen which is removed from the bottom of the
column
G The fractions obtained from crude oil can be used as fuels or may be further
processed to produce petrochemicals
Alkanes and cycloalkanes are saturated hydrocarbons
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Boiling Points of Alkanes
VDW forces exist between the different alkane molecules in a fraction which have to be broken in
order for the mixture to boil
$ amp ( ) $(
Chain length increases intermolecular forces stronger boiling point increases More points of
contact between long-chained alkanes so more VDW forces It takes more energy and therefore a
higher temperature to separate the molecules
Isomers have the same molecular mass A branched isomer has a lower boiling point than an
unbranched isomer There are fewer points of contact when branched chains interact with other
molecules so fewer VDW forces between the molecules
Also branched molecules cannot get as close to each other as unbranched one so fewer
intermolecular forces so less energy required to separate the molecules and lower boiling point
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Short chain alkanes are valuable as clean fuels They burn in a plentiful supply of oxygen to form
carbon dioxide and water
Methane is the main constituent of natural gas and is used for domestic heating and cooking It
burns cleanly in oxygen
CH4(g) + 2O2(g) -----gt CO2(g) + 2H2O(l)
Propane and butane are easily liquefied and are known as liquefied petroleum gas or LPG They are
used as fuels in barbecues patio heaters and portable cooking appliances
Octane is present in petrol used to fuel internal combustion engines
C8H18(g) + 12+
O2(g) -----gt 8CO2(g) + 9H2O(l)
Incomplete Combustion
The internal combustion engine in most cars has a limited supply of oxygen so some of the octane
will undergo incomplete combustion forming carbon monoxide instead of carbon dioxide
C8H18(g) + 8+
O2(g) -----gt 8CO(g) + 9H2O(l)
CO is a colourless odourless gas produced when a fossil fuel is burned with an insufficient supply of
oxygen It is poisonous prevents the haemoglobin in RBCs from binding with oxygen and the bodyrsquos
tissues become starved of oxygen which can be fatal At home CO can be formed form faulty
heating systems blocked chimneys or inadequate ventilation CO detectors protect the home from
the toxic effects of CO
NB In combustion equations C02 molecules = No of carbon atoms in HC and H2O molecules = -
No
Of hydrogen atoms
After fractional distillation there are lots of long-chained hydrocarbons however there is high
demand for short-chained hydrocarbons for use as a) fuels and b)polymer production
Cracking ndash The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-
chained alkanes and alkenes
In catalytic cracking long chained alkanes are broken randomly There are many possible equations
for cracking a particular starting material In catalytic cracking the equations must be balanced and a
mixture of alkanes and alkenes is always formed Most catalytic cracking uses a zeolite catalyst at
450degC
Branched Alkanes can be formed by a process called isomerisation which converts unbranched
alkanes into branched alkanes
Cyclic Hydrocarbons can be produced in a process called reforming where aliphatic hydrocarbons
are converted into cyclic or aromatic hydrocarbons hydrogen is also produced
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Improving Fuels
The Research Octane Number (RON) rates how well a fuel burns Fuels with high octane ratings close
to 100 burn efficiently Heptane (straight-chained alkane) is a poor fuel and has an RON of 0
Branched and cyclic alkanes are important petrol additives they promote more efficient combustion
that straight-chain alkanes Also branched alkanes are used in fuels for car engines
The hydrogen produced during reforming is used in other chemical processes such as ammonia and
margarine production This is a good example of using by-products to make other useful products
We have come to rely on crude oil as a source of power for electrical generation and for transport
Many chemicals produced from crude oil have become important feedstock for the chemical
industry over 90 of crude oil is used for fuel Every day items can be made from petrochemicals
The Earthrsquos deposits of crude oil are depleting at a fast rate
Many of the fuels produced are alkanes Branched and cyclic alkanes are amongst the best fuels A
good fuel needs to be readily available easily transported and inexpensive Oil is suitable but
recently its price has increased significantly and scientists are now looking into alternatives to fossil
fuels
At the start of this century the publicrsquos opinion and concern for the environment has shifted all
hydrocarbons produce pollutants The over reliance on crude oil as for fuel has led environmentalists
to call for urgent actionso it is not only the price of oil that has caused scientists to look for
alternative forms of energy
Burning hydrocarbons leads to an increase in atmospheric pollutants such as
bull Carbon monoxide ndashToxic gas formed by incomplete combustion in internal combustion
engine
bull Carbon dioxide ndash Major contributor o global warming (greenhouse effect)
bull Nitrogen oxides ndash Contributors to acid rain and destruction of forests
bull Sulphur dioxide ndash Acid rain
Global Warming
Refers to an increase in the Earthrsquos average temperature There is growing evidence that this could
be related to human activity such as burning fossil fuels which releases carbon dioxide and other
greenhouse gases into the atmosphere These gases prevent heat from escaping the atmosphere
and leads to increased temperatures on Earth A warmer planet may mean a change in climate with
heavier rain and more frequent violent storms Temperature change also threatens to melt the
polar ice caps which could result in sea levels rising and localised flooding This will have an impact
on all plant and animal forms and will lead to a change in lifestyle
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Fuels for the Future
A biofuel is a fuel that is derived from recently living material such as plants or animal waste
Agricultural crops grown for energy use include sugar cane and rape
Ethanol can be made by fermenting sugar and other carbohydrates It burns efficiently in a plentiful
supply of oxygen to give carbon dioxide and water Ethanol can be blended with petroleum for a fuel
that burns more efficiently Ethanol blends can be used in engines without modifications This
reduces harmful exhaust emissions
Bioethanol is getting a big boost in the UK as the countryrsquos first plants become operational
Biodiesel is a fuel oil derived from natural resources such as plants Rapeseed is the most popular
source in Europe Biodiesel can be used 100 pure in compatible engines however it is normally
blended with normal diesel
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Alkanes react with halogens n the presence of UV radiation or at a temperature of 300degC
This reaction is called Radical Substitution ndash A radical replaces a different atom or group of atoms in
a molecule
bull Covalent bonds are broken by homolytic fission to form radicals
bull A hydrogen atom in the alkane is substituted by a halogen atom
Eg methane reacts with chlorine to produce chloromethane
CH4 + Cl2 -----gt CH3Cl + HCl
Mechanism
Initiation
Cl ndash Cl -----gt Cl + Cl
Propagation
1 CH4+ Cl -----gt CH3 + HCl
2 CH3 + Cl2 -----gt CH3Cl + Cl
Termination
Cl + Cl -----gt Cl2
Cl + CH3 -----gt CH3Cl
CH3 + CH3 -----gt C2H6
Further Reactions of Chloromethane
Other organic products can form in the propagation stage
In the termination stage Chlorine Ethane and chloromethane are formed However chloromethane
may react further with chlorine radicals until all of the hydrogen radicals have been replaced which
results in a mixture of chloromethane dichloromethane trichloromethane and tetrachloromethane
The free radicals are generated
by ultraviolet radiation
The two repeated steps that
build up the products in a chain
reaction Propagations reactions
are rapid and continue until no
reactants remain
Two radicals combine to form a
molecule
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Limitations of Radicals in Synthesis
Every cell in the body produces tens of thousands of radicals every day they are a by-product of cell
metabolism such as form fighting infection or burning glucose for energy they are important in
hormone and enzyme production
Exposure to radicals is linked to premature aging Radicals can damage cell membranes of all cells
and DNA The body has antioxidants that keep radicals in check and protect the body against the
harmful effects of radicals Antioxidants are vitamins C and E We are also exposed to radicals from
cigarette smoke sunbathing pollution and food contaminated with herbicides
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
H
C C
H
H
Alkenes and cycloalkenes are unsaturated hydrocarbons Alkenes have at least one C=C double
bond Aliphatic alkenes with one double bond have the general formula CnH2n They are more
reactive than alkanes and typically take part in addition reactions They can form EZ isomers
including cis-trans isomers
A π-bond is the reactive part of a double bond formed above and below the plane of bonded atoms
by the sideways overlap of p-orbitals Each carbon atom contributes one electron from a p-orbital to
the electron pair in the π-bond which fixes the carbon atoms in position and prevents any rotation
of the bond In alkenes each carbon uses 3 electrons in 3 σ-bonds and 1 electron in one π-bond
Shape of Alkenes
3 regions of electron density surround each carbon atoms in a double bond Pairs of electrons repel
each other as far apart as possible The electron pairs repel each other to give a trigonal planar
shape (120deg)
Cyclic alkenes can be treated the same as branched or straight chained alkenes ndash the react in the
same way
Alkenes are more reactive than alkanes because of the C=C double bond Bond enthalpies show that
a double bond is stronger than a single bond and a π-bond is weaker than a σ-bond When an alkene
breaks the π-bond breaks and the σ-bond stays intact
H
H
C C
H
H
P-orbitals overlap
σ-bond σ-bond
π-bond
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Ni
150degC
C
H
H C
H
H H
H
H
C C
H
H H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
Alkene Reactions
Typically addition reactions
1 A small molecule is added across the double bond causing the π-bond to break
2 2 reactant molecules react together to form on product
3 An unsaturated alkene reacts and forms a saturated alkane
Hydrogenation of Ethene
This is an example of reduction
Halogenation of Ethene
When bromine is added to an alkene sample the colour changes from orange to
colourless The colour change indicates bromine has reacted with the double bond
This is a test for unsaturation it shows the presence of a C=C double bond
Addition of Hydrogen Halides
Hydration of Ethene
A method of preparing alcohols
+ H2
+ Cl2
+ HBr
+ H2O(g) H3PO4
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
C C
H
H H
C
H
H C
H
H H
+
C
H
H C
H
H H
+ C
H
H C
H
H Br
H
Addition of Hydrogen Bromide (electrophilic addition)
+
Hδ+
Brδ-
Br -
Br -
bull In this reaction HBr is
the electrophile
electron pair acceptor
bull HBr is a polar
molecule but non-
polar molecules can
also react with
alkenes
bull The HBr bond breaks
by heterolytic fission
When bromine is added to an
alkene
bull The electrons in the π-
bond repel those in
the Br-Br bond
inducing a dipole in
Br2
bull This forms a
carbocation and a
bromide ion
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
B
C C
A
E D
n C
H
C
H
Cl Cl n
Polymer - A long molecular chain built up from monomer units
Monomer ndash Small molecule that combines with others to form a polymer
If the monomers are alkenes many monomers can be added together to form a long polymer chain
This process is called addition polymerisation
Addition Polymer ndash Very long molecular chain formed by repeated addition reactions of unsaturated
alkene molecules (monomers)
Monomer Polymer (repeated unit)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
The Use of Alkenes
Margarine
The word used for a substance to substitute butter It is made from fats mixed with skimmed milk
and salt Margarine from veg oil is becoming popular for good health people are refusing animal fats
in their diets Margarine with high mono- or polyunsaturated fats are said to be healthier than
butterother margarines Often made from sunflowerolive oil
Veg oils are liquids containing long hydrocarbon chains with many double bonds and are
polyunsaturated The oil must be hardened so it can be spread without being soaked into bread
The oils are hardened by hydrogenation which adds hydrogen molecules across double bonds in an
addition reaction It alters the individual molecule so that the oil partially solidifies and hardens By
adding hydrogen molecules across different numbers of double bonds hardness can vary and
spreadability of margarine can be controlled Partial hydrogenation of unsaturated fats can
transform cis double bonds into trans double bonds as a by-product trans fats are thought to be bad
for health
Poly(phenylethene) Polystyrene is a cheap plastic used in foam packaging insulation model-making
and food retail Polystyrene is being replaced with biodegradable materials as environmental
pressure increases
Poly(propene)Polypropylene is used in food packaging dishwasher safe containers carpet fibres
synthetic ropes It is resistant to chemical attack so is used in certain lab equipment
Addition polymers are durable and do not break down naturally which makes them very useful but
their disposal poses problems
Processing of Waste Polymers
The best way to protect the environment is to re-use polymers without processing
Separation into Types and Recycling
Before plastic waste can be processedconverted it must be sorted Polymer ID codes are used to do
this Optical scanning techniques can separate PET from HDPE bottles Other technologies can
distinguish PVC from other plastics A small quantity of PVC in PET can render the product unsuitable
for re-use PVC is known to release poisonous dioxins when heated
Reclamation
This involves mechanically chopping polymers into small flakes then washing them to remove
impurities The flakes are sent to manufacturing companies where new materials are made by
melting the pellets and remoulding them
PET bottles are converted into carpets clothing and new bottles
HDPE is re-used to make plastic boxes water butts and bins
LDPE waste is made into plastic refuse sacks
Polymers as a Fuel Source
Burning polymers produces heat energy which can be harnessed to generate electricity Agricultural
plastics are being turned into briquettes and are being burned for heat
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
bull Homologous series A series of organic compound shaving the same functional group but with each successive member differing by CH 2
bull Functional Group A group of atoms responsible for the characteristic reactions of a compound
Alkanes Homologous Series
Number of carbons Name Formula
1 Methane CH4
2 Ethane C2H6
3 Propane C3H8
4 Butane C4H10
5 Pentane C5H12
6 Hexane C6H14
7 Heptane C7H16
8 Octane C8H18 9 Nonane C9H20
10 Decane C10H22
bull Hydrocarbon A compound of carbon and hydrogen only
bull Saturated Hydrocarbon A hydrocarbon with single bonds only
bull Unsaturated Hydrocarbon Contains carbon-carbon multiple bonds
bull Aliphatic hydrocarbon A hydrocarbon in which the carbon atoms are joined together in unbranched or branched chains
bull Alicyclic Hydrocarbon A hydrocarbon in which the carbons are joined together in a ring structure
Carbon is in group 4 of the periodic table it has 4 electrons in the outer shell which pair up
with electrons in other atoms to form 4 covalent bonds
Alkanes re saturated hydrocarbons with single C-C bonds only Each carbon atom is bonded to
four other atoms Each carbon has a tetrahedral shape (1095)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
A
C C
H
H A
A
C C
A
H H
B
C C
A
A C
A
C C
A
C B
bull Structural Isomers Compounds with the same molecular formula but different structural formula
bull Stereoisomers Compounds with the same structural formula but with a different arrangement in space
bull EZ isomerism An example of stereoisomerism in terms of restricted rotation about a double bond and the requirement for two different groups to be attached to each carbon atom of the C=C group E Isomerism Z Isomerism
bull Cis-trans isomerism A special case of EZ isomerism in which two substituent groups are the same
CIS TRANS
oppositE
Together
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Type of Compound Formula Prefix Suffix
Alkane C-C -ane Alkene C=C -ene Halogenoalkane -F
-CL -Br -I
Fluoro- Chloro- Bromo- Iodo-
Alcohol -OH -ol Aldehyde -CHO
-al
Ketone C-CO-C
-one
Carboxylic acid -COOH
-oic acid
O
C
OH
C C C
O
O
C
H
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
During a chemical reaction bonds are broken in a process called bond fission A covalent
bond can be broken in two ways
bull Homolytic Fission
1 Each bonded atom takes one of the shared pair of electrons
2 Each atom now has an unpaired electron and is called a radical
3 Two species of the same type (lsquohomorsquolytic) are produced
X ndash Y -----gt X + Y
bull Heterolytic Fission
1 One of the bonded atoms takes both of the electrons in the shared pair
2 Two ions are produced
3 The atom that takes both electrons becomes negatively charged (anion)
4 The atom that does not take the shared electron becomes positively charged
(cation)
X ndash Y -----gt X+ + Y-
bull Nucleophile An electron pair donor
bull Electrophile An electron pair acceptor
bull Addition reaction A molecule is added across the double bond of an unsaturated molecule to make a saturated molecule
2 reactants -----gt 1 product
bull Substitution reaction An atom or group of atoms is replaced with a different atom or groups of atoms
2 reactants -----gt 2 products
bull Elimination Reaction The removal of a molecule from a saturated molecule to make a saturated molecule
1 reactant -----gt 2 products
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Percentage Yield
100 yields are rarely achieved possible causes are
bull The reaction may be at equilibrium and may not go to completion
bull Other side reactions may occur leading to by-products
bull The reactants may not be pure
bull Some of the reactants or products may be left behind in the apparatus
bull Separation and purification may result in the loss of some of the product
1313
1313
A Limiting Reagent is the substance in a chemical reaction that runs out first
Atom Economy
A reaction may produce by-products along with the desired product
What can be done with by-products
1 If it is considered to be waste by-products are disposed of This is costly and poses
potential environmental problems
2 By-products may be sold on or used elsewhere in the chemical plant This practice is
likely to increase in the future as we become increasingly concerned about
preserving the earthrsquos resources and minimising waste
Atom economy considers not only the desired product but also the by-products in a chemical
reaction It describes the efficiency of a reaction in terms of all atoms involved High atom economy
means minimal waste
1313 1313
1313
bull Addition reactions 100 atom economy
bull Substitution and Elimination reactions lt 100 atom economy
How can atom economy benefit society
By using products with higher atom economy chemical companies can reduce the amount of waste
produced which is also good for the environment since we a re running out of landfill sites It has
also been suggested that 5-10 of the expenditure of a chemical company goes on waste treatment
bull Percentage yield tells you the efficiency of converting reactants into products
bull Atom economy tells you the proportion of desired products compares with all the products
formed
bull A reaction may have a high percentage yield but a low atom economy
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Hydrocarbons from crude oil
Hydrocarbons are organic compounds containing hydrogen and carbon only
Crude oil is a fossil fuel made from naturally decaying plants and animals that once lived in ancient
seas millions of years ago It is a mixture of over 150 different hydrocarbons most of which are
unbranched Crude oil does not ignite easily so is not useful in its native state However some of its
components are valuable and are used in petrol kerosene and heating and lubricating oils
Fractional Distillation - The separation of the components of crude oil into fractions which differ in
boiling point by means of distillation
Crude oil is refined in a distillation plant
1 The mixture of hydrocarbons is separate into fractions
2 Each fraction consists of a mixture of hydrocarbons with similar boiling points
3 Pure liquids have a fixed boiling point A pure hydrocarbon can be obtained by
further distillation of a crude oil fraction
The process takes place in a fractionating column
A The crude oil is vaporised and then passed into the fractionating column The
column is hotter at the bottom than the top and the gases pass up the column
through a series of bubble caps
B Eventually the gases reach a temperature that is lower than their boiling points
Here the vapour condenses to a liquid The liquid fractions are then tapped off into
storage containers
C Short chained hydrocarbons with lower boiling points condense near the top of the
column
D Longer chained hydrocarbons with higher boiling points condense near the bottom
E Gases which do not condense pass through the top of the column as lsquopetroleum gasrsquo
F The residue from the process is bitumen which is removed from the bottom of the
column
G The fractions obtained from crude oil can be used as fuels or may be further
processed to produce petrochemicals
Alkanes and cycloalkanes are saturated hydrocarbons
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Boiling Points of Alkanes
VDW forces exist between the different alkane molecules in a fraction which have to be broken in
order for the mixture to boil
$ amp ( ) $(
Chain length increases intermolecular forces stronger boiling point increases More points of
contact between long-chained alkanes so more VDW forces It takes more energy and therefore a
higher temperature to separate the molecules
Isomers have the same molecular mass A branched isomer has a lower boiling point than an
unbranched isomer There are fewer points of contact when branched chains interact with other
molecules so fewer VDW forces between the molecules
Also branched molecules cannot get as close to each other as unbranched one so fewer
intermolecular forces so less energy required to separate the molecules and lower boiling point
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Short chain alkanes are valuable as clean fuels They burn in a plentiful supply of oxygen to form
carbon dioxide and water
Methane is the main constituent of natural gas and is used for domestic heating and cooking It
burns cleanly in oxygen
CH4(g) + 2O2(g) -----gt CO2(g) + 2H2O(l)
Propane and butane are easily liquefied and are known as liquefied petroleum gas or LPG They are
used as fuels in barbecues patio heaters and portable cooking appliances
Octane is present in petrol used to fuel internal combustion engines
C8H18(g) + 12+
O2(g) -----gt 8CO2(g) + 9H2O(l)
Incomplete Combustion
The internal combustion engine in most cars has a limited supply of oxygen so some of the octane
will undergo incomplete combustion forming carbon monoxide instead of carbon dioxide
C8H18(g) + 8+
O2(g) -----gt 8CO(g) + 9H2O(l)
CO is a colourless odourless gas produced when a fossil fuel is burned with an insufficient supply of
oxygen It is poisonous prevents the haemoglobin in RBCs from binding with oxygen and the bodyrsquos
tissues become starved of oxygen which can be fatal At home CO can be formed form faulty
heating systems blocked chimneys or inadequate ventilation CO detectors protect the home from
the toxic effects of CO
NB In combustion equations C02 molecules = No of carbon atoms in HC and H2O molecules = -
No
Of hydrogen atoms
After fractional distillation there are lots of long-chained hydrocarbons however there is high
demand for short-chained hydrocarbons for use as a) fuels and b)polymer production
Cracking ndash The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-
chained alkanes and alkenes
In catalytic cracking long chained alkanes are broken randomly There are many possible equations
for cracking a particular starting material In catalytic cracking the equations must be balanced and a
mixture of alkanes and alkenes is always formed Most catalytic cracking uses a zeolite catalyst at
450degC
Branched Alkanes can be formed by a process called isomerisation which converts unbranched
alkanes into branched alkanes
Cyclic Hydrocarbons can be produced in a process called reforming where aliphatic hydrocarbons
are converted into cyclic or aromatic hydrocarbons hydrogen is also produced
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Improving Fuels
The Research Octane Number (RON) rates how well a fuel burns Fuels with high octane ratings close
to 100 burn efficiently Heptane (straight-chained alkane) is a poor fuel and has an RON of 0
Branched and cyclic alkanes are important petrol additives they promote more efficient combustion
that straight-chain alkanes Also branched alkanes are used in fuels for car engines
The hydrogen produced during reforming is used in other chemical processes such as ammonia and
margarine production This is a good example of using by-products to make other useful products
We have come to rely on crude oil as a source of power for electrical generation and for transport
Many chemicals produced from crude oil have become important feedstock for the chemical
industry over 90 of crude oil is used for fuel Every day items can be made from petrochemicals
The Earthrsquos deposits of crude oil are depleting at a fast rate
Many of the fuels produced are alkanes Branched and cyclic alkanes are amongst the best fuels A
good fuel needs to be readily available easily transported and inexpensive Oil is suitable but
recently its price has increased significantly and scientists are now looking into alternatives to fossil
fuels
At the start of this century the publicrsquos opinion and concern for the environment has shifted all
hydrocarbons produce pollutants The over reliance on crude oil as for fuel has led environmentalists
to call for urgent actionso it is not only the price of oil that has caused scientists to look for
alternative forms of energy
Burning hydrocarbons leads to an increase in atmospheric pollutants such as
bull Carbon monoxide ndashToxic gas formed by incomplete combustion in internal combustion
engine
bull Carbon dioxide ndash Major contributor o global warming (greenhouse effect)
bull Nitrogen oxides ndash Contributors to acid rain and destruction of forests
bull Sulphur dioxide ndash Acid rain
Global Warming
Refers to an increase in the Earthrsquos average temperature There is growing evidence that this could
be related to human activity such as burning fossil fuels which releases carbon dioxide and other
greenhouse gases into the atmosphere These gases prevent heat from escaping the atmosphere
and leads to increased temperatures on Earth A warmer planet may mean a change in climate with
heavier rain and more frequent violent storms Temperature change also threatens to melt the
polar ice caps which could result in sea levels rising and localised flooding This will have an impact
on all plant and animal forms and will lead to a change in lifestyle
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Fuels for the Future
A biofuel is a fuel that is derived from recently living material such as plants or animal waste
Agricultural crops grown for energy use include sugar cane and rape
Ethanol can be made by fermenting sugar and other carbohydrates It burns efficiently in a plentiful
supply of oxygen to give carbon dioxide and water Ethanol can be blended with petroleum for a fuel
that burns more efficiently Ethanol blends can be used in engines without modifications This
reduces harmful exhaust emissions
Bioethanol is getting a big boost in the UK as the countryrsquos first plants become operational
Biodiesel is a fuel oil derived from natural resources such as plants Rapeseed is the most popular
source in Europe Biodiesel can be used 100 pure in compatible engines however it is normally
blended with normal diesel
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Alkanes react with halogens n the presence of UV radiation or at a temperature of 300degC
This reaction is called Radical Substitution ndash A radical replaces a different atom or group of atoms in
a molecule
bull Covalent bonds are broken by homolytic fission to form radicals
bull A hydrogen atom in the alkane is substituted by a halogen atom
Eg methane reacts with chlorine to produce chloromethane
CH4 + Cl2 -----gt CH3Cl + HCl
Mechanism
Initiation
Cl ndash Cl -----gt Cl + Cl
Propagation
1 CH4+ Cl -----gt CH3 + HCl
2 CH3 + Cl2 -----gt CH3Cl + Cl
Termination
Cl + Cl -----gt Cl2
Cl + CH3 -----gt CH3Cl
CH3 + CH3 -----gt C2H6
Further Reactions of Chloromethane
Other organic products can form in the propagation stage
In the termination stage Chlorine Ethane and chloromethane are formed However chloromethane
may react further with chlorine radicals until all of the hydrogen radicals have been replaced which
results in a mixture of chloromethane dichloromethane trichloromethane and tetrachloromethane
The free radicals are generated
by ultraviolet radiation
The two repeated steps that
build up the products in a chain
reaction Propagations reactions
are rapid and continue until no
reactants remain
Two radicals combine to form a
molecule
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Limitations of Radicals in Synthesis
Every cell in the body produces tens of thousands of radicals every day they are a by-product of cell
metabolism such as form fighting infection or burning glucose for energy they are important in
hormone and enzyme production
Exposure to radicals is linked to premature aging Radicals can damage cell membranes of all cells
and DNA The body has antioxidants that keep radicals in check and protect the body against the
harmful effects of radicals Antioxidants are vitamins C and E We are also exposed to radicals from
cigarette smoke sunbathing pollution and food contaminated with herbicides
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
H
C C
H
H
Alkenes and cycloalkenes are unsaturated hydrocarbons Alkenes have at least one C=C double
bond Aliphatic alkenes with one double bond have the general formula CnH2n They are more
reactive than alkanes and typically take part in addition reactions They can form EZ isomers
including cis-trans isomers
A π-bond is the reactive part of a double bond formed above and below the plane of bonded atoms
by the sideways overlap of p-orbitals Each carbon atom contributes one electron from a p-orbital to
the electron pair in the π-bond which fixes the carbon atoms in position and prevents any rotation
of the bond In alkenes each carbon uses 3 electrons in 3 σ-bonds and 1 electron in one π-bond
Shape of Alkenes
3 regions of electron density surround each carbon atoms in a double bond Pairs of electrons repel
each other as far apart as possible The electron pairs repel each other to give a trigonal planar
shape (120deg)
Cyclic alkenes can be treated the same as branched or straight chained alkenes ndash the react in the
same way
Alkenes are more reactive than alkanes because of the C=C double bond Bond enthalpies show that
a double bond is stronger than a single bond and a π-bond is weaker than a σ-bond When an alkene
breaks the π-bond breaks and the σ-bond stays intact
H
H
C C
H
H
P-orbitals overlap
σ-bond σ-bond
π-bond
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Ni
150degC
C
H
H C
H
H H
H
H
C C
H
H H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
Alkene Reactions
Typically addition reactions
1 A small molecule is added across the double bond causing the π-bond to break
2 2 reactant molecules react together to form on product
3 An unsaturated alkene reacts and forms a saturated alkane
Hydrogenation of Ethene
This is an example of reduction
Halogenation of Ethene
When bromine is added to an alkene sample the colour changes from orange to
colourless The colour change indicates bromine has reacted with the double bond
This is a test for unsaturation it shows the presence of a C=C double bond
Addition of Hydrogen Halides
Hydration of Ethene
A method of preparing alcohols
+ H2
+ Cl2
+ HBr
+ H2O(g) H3PO4
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
C C
H
H H
C
H
H C
H
H H
+
C
H
H C
H
H H
+ C
H
H C
H
H Br
H
Addition of Hydrogen Bromide (electrophilic addition)
+
Hδ+
Brδ-
Br -
Br -
bull In this reaction HBr is
the electrophile
electron pair acceptor
bull HBr is a polar
molecule but non-
polar molecules can
also react with
alkenes
bull The HBr bond breaks
by heterolytic fission
When bromine is added to an
alkene
bull The electrons in the π-
bond repel those in
the Br-Br bond
inducing a dipole in
Br2
bull This forms a
carbocation and a
bromide ion
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
B
C C
A
E D
n C
H
C
H
Cl Cl n
Polymer - A long molecular chain built up from monomer units
Monomer ndash Small molecule that combines with others to form a polymer
If the monomers are alkenes many monomers can be added together to form a long polymer chain
This process is called addition polymerisation
Addition Polymer ndash Very long molecular chain formed by repeated addition reactions of unsaturated
alkene molecules (monomers)
Monomer Polymer (repeated unit)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
The Use of Alkenes
Margarine
The word used for a substance to substitute butter It is made from fats mixed with skimmed milk
and salt Margarine from veg oil is becoming popular for good health people are refusing animal fats
in their diets Margarine with high mono- or polyunsaturated fats are said to be healthier than
butterother margarines Often made from sunflowerolive oil
Veg oils are liquids containing long hydrocarbon chains with many double bonds and are
polyunsaturated The oil must be hardened so it can be spread without being soaked into bread
The oils are hardened by hydrogenation which adds hydrogen molecules across double bonds in an
addition reaction It alters the individual molecule so that the oil partially solidifies and hardens By
adding hydrogen molecules across different numbers of double bonds hardness can vary and
spreadability of margarine can be controlled Partial hydrogenation of unsaturated fats can
transform cis double bonds into trans double bonds as a by-product trans fats are thought to be bad
for health
Poly(phenylethene) Polystyrene is a cheap plastic used in foam packaging insulation model-making
and food retail Polystyrene is being replaced with biodegradable materials as environmental
pressure increases
Poly(propene)Polypropylene is used in food packaging dishwasher safe containers carpet fibres
synthetic ropes It is resistant to chemical attack so is used in certain lab equipment
Addition polymers are durable and do not break down naturally which makes them very useful but
their disposal poses problems
Processing of Waste Polymers
The best way to protect the environment is to re-use polymers without processing
Separation into Types and Recycling
Before plastic waste can be processedconverted it must be sorted Polymer ID codes are used to do
this Optical scanning techniques can separate PET from HDPE bottles Other technologies can
distinguish PVC from other plastics A small quantity of PVC in PET can render the product unsuitable
for re-use PVC is known to release poisonous dioxins when heated
Reclamation
This involves mechanically chopping polymers into small flakes then washing them to remove
impurities The flakes are sent to manufacturing companies where new materials are made by
melting the pellets and remoulding them
PET bottles are converted into carpets clothing and new bottles
HDPE is re-used to make plastic boxes water butts and bins
LDPE waste is made into plastic refuse sacks
Polymers as a Fuel Source
Burning polymers produces heat energy which can be harnessed to generate electricity Agricultural
plastics are being turned into briquettes and are being burned for heat
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
A
C C
H
H A
A
C C
A
H H
B
C C
A
A C
A
C C
A
C B
bull Structural Isomers Compounds with the same molecular formula but different structural formula
bull Stereoisomers Compounds with the same structural formula but with a different arrangement in space
bull EZ isomerism An example of stereoisomerism in terms of restricted rotation about a double bond and the requirement for two different groups to be attached to each carbon atom of the C=C group E Isomerism Z Isomerism
bull Cis-trans isomerism A special case of EZ isomerism in which two substituent groups are the same
CIS TRANS
oppositE
Together
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Type of Compound Formula Prefix Suffix
Alkane C-C -ane Alkene C=C -ene Halogenoalkane -F
-CL -Br -I
Fluoro- Chloro- Bromo- Iodo-
Alcohol -OH -ol Aldehyde -CHO
-al
Ketone C-CO-C
-one
Carboxylic acid -COOH
-oic acid
O
C
OH
C C C
O
O
C
H
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
During a chemical reaction bonds are broken in a process called bond fission A covalent
bond can be broken in two ways
bull Homolytic Fission
1 Each bonded atom takes one of the shared pair of electrons
2 Each atom now has an unpaired electron and is called a radical
3 Two species of the same type (lsquohomorsquolytic) are produced
X ndash Y -----gt X + Y
bull Heterolytic Fission
1 One of the bonded atoms takes both of the electrons in the shared pair
2 Two ions are produced
3 The atom that takes both electrons becomes negatively charged (anion)
4 The atom that does not take the shared electron becomes positively charged
(cation)
X ndash Y -----gt X+ + Y-
bull Nucleophile An electron pair donor
bull Electrophile An electron pair acceptor
bull Addition reaction A molecule is added across the double bond of an unsaturated molecule to make a saturated molecule
2 reactants -----gt 1 product
bull Substitution reaction An atom or group of atoms is replaced with a different atom or groups of atoms
2 reactants -----gt 2 products
bull Elimination Reaction The removal of a molecule from a saturated molecule to make a saturated molecule
1 reactant -----gt 2 products
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Percentage Yield
100 yields are rarely achieved possible causes are
bull The reaction may be at equilibrium and may not go to completion
bull Other side reactions may occur leading to by-products
bull The reactants may not be pure
bull Some of the reactants or products may be left behind in the apparatus
bull Separation and purification may result in the loss of some of the product
1313
1313
A Limiting Reagent is the substance in a chemical reaction that runs out first
Atom Economy
A reaction may produce by-products along with the desired product
What can be done with by-products
1 If it is considered to be waste by-products are disposed of This is costly and poses
potential environmental problems
2 By-products may be sold on or used elsewhere in the chemical plant This practice is
likely to increase in the future as we become increasingly concerned about
preserving the earthrsquos resources and minimising waste
Atom economy considers not only the desired product but also the by-products in a chemical
reaction It describes the efficiency of a reaction in terms of all atoms involved High atom economy
means minimal waste
1313 1313
1313
bull Addition reactions 100 atom economy
bull Substitution and Elimination reactions lt 100 atom economy
How can atom economy benefit society
By using products with higher atom economy chemical companies can reduce the amount of waste
produced which is also good for the environment since we a re running out of landfill sites It has
also been suggested that 5-10 of the expenditure of a chemical company goes on waste treatment
bull Percentage yield tells you the efficiency of converting reactants into products
bull Atom economy tells you the proportion of desired products compares with all the products
formed
bull A reaction may have a high percentage yield but a low atom economy
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Hydrocarbons from crude oil
Hydrocarbons are organic compounds containing hydrogen and carbon only
Crude oil is a fossil fuel made from naturally decaying plants and animals that once lived in ancient
seas millions of years ago It is a mixture of over 150 different hydrocarbons most of which are
unbranched Crude oil does not ignite easily so is not useful in its native state However some of its
components are valuable and are used in petrol kerosene and heating and lubricating oils
Fractional Distillation - The separation of the components of crude oil into fractions which differ in
boiling point by means of distillation
Crude oil is refined in a distillation plant
1 The mixture of hydrocarbons is separate into fractions
2 Each fraction consists of a mixture of hydrocarbons with similar boiling points
3 Pure liquids have a fixed boiling point A pure hydrocarbon can be obtained by
further distillation of a crude oil fraction
The process takes place in a fractionating column
A The crude oil is vaporised and then passed into the fractionating column The
column is hotter at the bottom than the top and the gases pass up the column
through a series of bubble caps
B Eventually the gases reach a temperature that is lower than their boiling points
Here the vapour condenses to a liquid The liquid fractions are then tapped off into
storage containers
C Short chained hydrocarbons with lower boiling points condense near the top of the
column
D Longer chained hydrocarbons with higher boiling points condense near the bottom
E Gases which do not condense pass through the top of the column as lsquopetroleum gasrsquo
F The residue from the process is bitumen which is removed from the bottom of the
column
G The fractions obtained from crude oil can be used as fuels or may be further
processed to produce petrochemicals
Alkanes and cycloalkanes are saturated hydrocarbons
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Boiling Points of Alkanes
VDW forces exist between the different alkane molecules in a fraction which have to be broken in
order for the mixture to boil
$ amp ( ) $(
Chain length increases intermolecular forces stronger boiling point increases More points of
contact between long-chained alkanes so more VDW forces It takes more energy and therefore a
higher temperature to separate the molecules
Isomers have the same molecular mass A branched isomer has a lower boiling point than an
unbranched isomer There are fewer points of contact when branched chains interact with other
molecules so fewer VDW forces between the molecules
Also branched molecules cannot get as close to each other as unbranched one so fewer
intermolecular forces so less energy required to separate the molecules and lower boiling point
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Short chain alkanes are valuable as clean fuels They burn in a plentiful supply of oxygen to form
carbon dioxide and water
Methane is the main constituent of natural gas and is used for domestic heating and cooking It
burns cleanly in oxygen
CH4(g) + 2O2(g) -----gt CO2(g) + 2H2O(l)
Propane and butane are easily liquefied and are known as liquefied petroleum gas or LPG They are
used as fuels in barbecues patio heaters and portable cooking appliances
Octane is present in petrol used to fuel internal combustion engines
C8H18(g) + 12+
O2(g) -----gt 8CO2(g) + 9H2O(l)
Incomplete Combustion
The internal combustion engine in most cars has a limited supply of oxygen so some of the octane
will undergo incomplete combustion forming carbon monoxide instead of carbon dioxide
C8H18(g) + 8+
O2(g) -----gt 8CO(g) + 9H2O(l)
CO is a colourless odourless gas produced when a fossil fuel is burned with an insufficient supply of
oxygen It is poisonous prevents the haemoglobin in RBCs from binding with oxygen and the bodyrsquos
tissues become starved of oxygen which can be fatal At home CO can be formed form faulty
heating systems blocked chimneys or inadequate ventilation CO detectors protect the home from
the toxic effects of CO
NB In combustion equations C02 molecules = No of carbon atoms in HC and H2O molecules = -
No
Of hydrogen atoms
After fractional distillation there are lots of long-chained hydrocarbons however there is high
demand for short-chained hydrocarbons for use as a) fuels and b)polymer production
Cracking ndash The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-
chained alkanes and alkenes
In catalytic cracking long chained alkanes are broken randomly There are many possible equations
for cracking a particular starting material In catalytic cracking the equations must be balanced and a
mixture of alkanes and alkenes is always formed Most catalytic cracking uses a zeolite catalyst at
450degC
Branched Alkanes can be formed by a process called isomerisation which converts unbranched
alkanes into branched alkanes
Cyclic Hydrocarbons can be produced in a process called reforming where aliphatic hydrocarbons
are converted into cyclic or aromatic hydrocarbons hydrogen is also produced
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Improving Fuels
The Research Octane Number (RON) rates how well a fuel burns Fuels with high octane ratings close
to 100 burn efficiently Heptane (straight-chained alkane) is a poor fuel and has an RON of 0
Branched and cyclic alkanes are important petrol additives they promote more efficient combustion
that straight-chain alkanes Also branched alkanes are used in fuels for car engines
The hydrogen produced during reforming is used in other chemical processes such as ammonia and
margarine production This is a good example of using by-products to make other useful products
We have come to rely on crude oil as a source of power for electrical generation and for transport
Many chemicals produced from crude oil have become important feedstock for the chemical
industry over 90 of crude oil is used for fuel Every day items can be made from petrochemicals
The Earthrsquos deposits of crude oil are depleting at a fast rate
Many of the fuels produced are alkanes Branched and cyclic alkanes are amongst the best fuels A
good fuel needs to be readily available easily transported and inexpensive Oil is suitable but
recently its price has increased significantly and scientists are now looking into alternatives to fossil
fuels
At the start of this century the publicrsquos opinion and concern for the environment has shifted all
hydrocarbons produce pollutants The over reliance on crude oil as for fuel has led environmentalists
to call for urgent actionso it is not only the price of oil that has caused scientists to look for
alternative forms of energy
Burning hydrocarbons leads to an increase in atmospheric pollutants such as
bull Carbon monoxide ndashToxic gas formed by incomplete combustion in internal combustion
engine
bull Carbon dioxide ndash Major contributor o global warming (greenhouse effect)
bull Nitrogen oxides ndash Contributors to acid rain and destruction of forests
bull Sulphur dioxide ndash Acid rain
Global Warming
Refers to an increase in the Earthrsquos average temperature There is growing evidence that this could
be related to human activity such as burning fossil fuels which releases carbon dioxide and other
greenhouse gases into the atmosphere These gases prevent heat from escaping the atmosphere
and leads to increased temperatures on Earth A warmer planet may mean a change in climate with
heavier rain and more frequent violent storms Temperature change also threatens to melt the
polar ice caps which could result in sea levels rising and localised flooding This will have an impact
on all plant and animal forms and will lead to a change in lifestyle
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Fuels for the Future
A biofuel is a fuel that is derived from recently living material such as plants or animal waste
Agricultural crops grown for energy use include sugar cane and rape
Ethanol can be made by fermenting sugar and other carbohydrates It burns efficiently in a plentiful
supply of oxygen to give carbon dioxide and water Ethanol can be blended with petroleum for a fuel
that burns more efficiently Ethanol blends can be used in engines without modifications This
reduces harmful exhaust emissions
Bioethanol is getting a big boost in the UK as the countryrsquos first plants become operational
Biodiesel is a fuel oil derived from natural resources such as plants Rapeseed is the most popular
source in Europe Biodiesel can be used 100 pure in compatible engines however it is normally
blended with normal diesel
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Alkanes react with halogens n the presence of UV radiation or at a temperature of 300degC
This reaction is called Radical Substitution ndash A radical replaces a different atom or group of atoms in
a molecule
bull Covalent bonds are broken by homolytic fission to form radicals
bull A hydrogen atom in the alkane is substituted by a halogen atom
Eg methane reacts with chlorine to produce chloromethane
CH4 + Cl2 -----gt CH3Cl + HCl
Mechanism
Initiation
Cl ndash Cl -----gt Cl + Cl
Propagation
1 CH4+ Cl -----gt CH3 + HCl
2 CH3 + Cl2 -----gt CH3Cl + Cl
Termination
Cl + Cl -----gt Cl2
Cl + CH3 -----gt CH3Cl
CH3 + CH3 -----gt C2H6
Further Reactions of Chloromethane
Other organic products can form in the propagation stage
In the termination stage Chlorine Ethane and chloromethane are formed However chloromethane
may react further with chlorine radicals until all of the hydrogen radicals have been replaced which
results in a mixture of chloromethane dichloromethane trichloromethane and tetrachloromethane
The free radicals are generated
by ultraviolet radiation
The two repeated steps that
build up the products in a chain
reaction Propagations reactions
are rapid and continue until no
reactants remain
Two radicals combine to form a
molecule
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Limitations of Radicals in Synthesis
Every cell in the body produces tens of thousands of radicals every day they are a by-product of cell
metabolism such as form fighting infection or burning glucose for energy they are important in
hormone and enzyme production
Exposure to radicals is linked to premature aging Radicals can damage cell membranes of all cells
and DNA The body has antioxidants that keep radicals in check and protect the body against the
harmful effects of radicals Antioxidants are vitamins C and E We are also exposed to radicals from
cigarette smoke sunbathing pollution and food contaminated with herbicides
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
H
C C
H
H
Alkenes and cycloalkenes are unsaturated hydrocarbons Alkenes have at least one C=C double
bond Aliphatic alkenes with one double bond have the general formula CnH2n They are more
reactive than alkanes and typically take part in addition reactions They can form EZ isomers
including cis-trans isomers
A π-bond is the reactive part of a double bond formed above and below the plane of bonded atoms
by the sideways overlap of p-orbitals Each carbon atom contributes one electron from a p-orbital to
the electron pair in the π-bond which fixes the carbon atoms in position and prevents any rotation
of the bond In alkenes each carbon uses 3 electrons in 3 σ-bonds and 1 electron in one π-bond
Shape of Alkenes
3 regions of electron density surround each carbon atoms in a double bond Pairs of electrons repel
each other as far apart as possible The electron pairs repel each other to give a trigonal planar
shape (120deg)
Cyclic alkenes can be treated the same as branched or straight chained alkenes ndash the react in the
same way
Alkenes are more reactive than alkanes because of the C=C double bond Bond enthalpies show that
a double bond is stronger than a single bond and a π-bond is weaker than a σ-bond When an alkene
breaks the π-bond breaks and the σ-bond stays intact
H
H
C C
H
H
P-orbitals overlap
σ-bond σ-bond
π-bond
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Ni
150degC
C
H
H C
H
H H
H
H
C C
H
H H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
Alkene Reactions
Typically addition reactions
1 A small molecule is added across the double bond causing the π-bond to break
2 2 reactant molecules react together to form on product
3 An unsaturated alkene reacts and forms a saturated alkane
Hydrogenation of Ethene
This is an example of reduction
Halogenation of Ethene
When bromine is added to an alkene sample the colour changes from orange to
colourless The colour change indicates bromine has reacted with the double bond
This is a test for unsaturation it shows the presence of a C=C double bond
Addition of Hydrogen Halides
Hydration of Ethene
A method of preparing alcohols
+ H2
+ Cl2
+ HBr
+ H2O(g) H3PO4
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
C C
H
H H
C
H
H C
H
H H
+
C
H
H C
H
H H
+ C
H
H C
H
H Br
H
Addition of Hydrogen Bromide (electrophilic addition)
+
Hδ+
Brδ-
Br -
Br -
bull In this reaction HBr is
the electrophile
electron pair acceptor
bull HBr is a polar
molecule but non-
polar molecules can
also react with
alkenes
bull The HBr bond breaks
by heterolytic fission
When bromine is added to an
alkene
bull The electrons in the π-
bond repel those in
the Br-Br bond
inducing a dipole in
Br2
bull This forms a
carbocation and a
bromide ion
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
B
C C
A
E D
n C
H
C
H
Cl Cl n
Polymer - A long molecular chain built up from monomer units
Monomer ndash Small molecule that combines with others to form a polymer
If the monomers are alkenes many monomers can be added together to form a long polymer chain
This process is called addition polymerisation
Addition Polymer ndash Very long molecular chain formed by repeated addition reactions of unsaturated
alkene molecules (monomers)
Monomer Polymer (repeated unit)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
The Use of Alkenes
Margarine
The word used for a substance to substitute butter It is made from fats mixed with skimmed milk
and salt Margarine from veg oil is becoming popular for good health people are refusing animal fats
in their diets Margarine with high mono- or polyunsaturated fats are said to be healthier than
butterother margarines Often made from sunflowerolive oil
Veg oils are liquids containing long hydrocarbon chains with many double bonds and are
polyunsaturated The oil must be hardened so it can be spread without being soaked into bread
The oils are hardened by hydrogenation which adds hydrogen molecules across double bonds in an
addition reaction It alters the individual molecule so that the oil partially solidifies and hardens By
adding hydrogen molecules across different numbers of double bonds hardness can vary and
spreadability of margarine can be controlled Partial hydrogenation of unsaturated fats can
transform cis double bonds into trans double bonds as a by-product trans fats are thought to be bad
for health
Poly(phenylethene) Polystyrene is a cheap plastic used in foam packaging insulation model-making
and food retail Polystyrene is being replaced with biodegradable materials as environmental
pressure increases
Poly(propene)Polypropylene is used in food packaging dishwasher safe containers carpet fibres
synthetic ropes It is resistant to chemical attack so is used in certain lab equipment
Addition polymers are durable and do not break down naturally which makes them very useful but
their disposal poses problems
Processing of Waste Polymers
The best way to protect the environment is to re-use polymers without processing
Separation into Types and Recycling
Before plastic waste can be processedconverted it must be sorted Polymer ID codes are used to do
this Optical scanning techniques can separate PET from HDPE bottles Other technologies can
distinguish PVC from other plastics A small quantity of PVC in PET can render the product unsuitable
for re-use PVC is known to release poisonous dioxins when heated
Reclamation
This involves mechanically chopping polymers into small flakes then washing them to remove
impurities The flakes are sent to manufacturing companies where new materials are made by
melting the pellets and remoulding them
PET bottles are converted into carpets clothing and new bottles
HDPE is re-used to make plastic boxes water butts and bins
LDPE waste is made into plastic refuse sacks
Polymers as a Fuel Source
Burning polymers produces heat energy which can be harnessed to generate electricity Agricultural
plastics are being turned into briquettes and are being burned for heat
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Type of Compound Formula Prefix Suffix
Alkane C-C -ane Alkene C=C -ene Halogenoalkane -F
-CL -Br -I
Fluoro- Chloro- Bromo- Iodo-
Alcohol -OH -ol Aldehyde -CHO
-al
Ketone C-CO-C
-one
Carboxylic acid -COOH
-oic acid
O
C
OH
C C C
O
O
C
H
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
During a chemical reaction bonds are broken in a process called bond fission A covalent
bond can be broken in two ways
bull Homolytic Fission
1 Each bonded atom takes one of the shared pair of electrons
2 Each atom now has an unpaired electron and is called a radical
3 Two species of the same type (lsquohomorsquolytic) are produced
X ndash Y -----gt X + Y
bull Heterolytic Fission
1 One of the bonded atoms takes both of the electrons in the shared pair
2 Two ions are produced
3 The atom that takes both electrons becomes negatively charged (anion)
4 The atom that does not take the shared electron becomes positively charged
(cation)
X ndash Y -----gt X+ + Y-
bull Nucleophile An electron pair donor
bull Electrophile An electron pair acceptor
bull Addition reaction A molecule is added across the double bond of an unsaturated molecule to make a saturated molecule
2 reactants -----gt 1 product
bull Substitution reaction An atom or group of atoms is replaced with a different atom or groups of atoms
2 reactants -----gt 2 products
bull Elimination Reaction The removal of a molecule from a saturated molecule to make a saturated molecule
1 reactant -----gt 2 products
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Percentage Yield
100 yields are rarely achieved possible causes are
bull The reaction may be at equilibrium and may not go to completion
bull Other side reactions may occur leading to by-products
bull The reactants may not be pure
bull Some of the reactants or products may be left behind in the apparatus
bull Separation and purification may result in the loss of some of the product
1313
1313
A Limiting Reagent is the substance in a chemical reaction that runs out first
Atom Economy
A reaction may produce by-products along with the desired product
What can be done with by-products
1 If it is considered to be waste by-products are disposed of This is costly and poses
potential environmental problems
2 By-products may be sold on or used elsewhere in the chemical plant This practice is
likely to increase in the future as we become increasingly concerned about
preserving the earthrsquos resources and minimising waste
Atom economy considers not only the desired product but also the by-products in a chemical
reaction It describes the efficiency of a reaction in terms of all atoms involved High atom economy
means minimal waste
1313 1313
1313
bull Addition reactions 100 atom economy
bull Substitution and Elimination reactions lt 100 atom economy
How can atom economy benefit society
By using products with higher atom economy chemical companies can reduce the amount of waste
produced which is also good for the environment since we a re running out of landfill sites It has
also been suggested that 5-10 of the expenditure of a chemical company goes on waste treatment
bull Percentage yield tells you the efficiency of converting reactants into products
bull Atom economy tells you the proportion of desired products compares with all the products
formed
bull A reaction may have a high percentage yield but a low atom economy
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Hydrocarbons from crude oil
Hydrocarbons are organic compounds containing hydrogen and carbon only
Crude oil is a fossil fuel made from naturally decaying plants and animals that once lived in ancient
seas millions of years ago It is a mixture of over 150 different hydrocarbons most of which are
unbranched Crude oil does not ignite easily so is not useful in its native state However some of its
components are valuable and are used in petrol kerosene and heating and lubricating oils
Fractional Distillation - The separation of the components of crude oil into fractions which differ in
boiling point by means of distillation
Crude oil is refined in a distillation plant
1 The mixture of hydrocarbons is separate into fractions
2 Each fraction consists of a mixture of hydrocarbons with similar boiling points
3 Pure liquids have a fixed boiling point A pure hydrocarbon can be obtained by
further distillation of a crude oil fraction
The process takes place in a fractionating column
A The crude oil is vaporised and then passed into the fractionating column The
column is hotter at the bottom than the top and the gases pass up the column
through a series of bubble caps
B Eventually the gases reach a temperature that is lower than their boiling points
Here the vapour condenses to a liquid The liquid fractions are then tapped off into
storage containers
C Short chained hydrocarbons with lower boiling points condense near the top of the
column
D Longer chained hydrocarbons with higher boiling points condense near the bottom
E Gases which do not condense pass through the top of the column as lsquopetroleum gasrsquo
F The residue from the process is bitumen which is removed from the bottom of the
column
G The fractions obtained from crude oil can be used as fuels or may be further
processed to produce petrochemicals
Alkanes and cycloalkanes are saturated hydrocarbons
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Boiling Points of Alkanes
VDW forces exist between the different alkane molecules in a fraction which have to be broken in
order for the mixture to boil
$ amp ( ) $(
Chain length increases intermolecular forces stronger boiling point increases More points of
contact between long-chained alkanes so more VDW forces It takes more energy and therefore a
higher temperature to separate the molecules
Isomers have the same molecular mass A branched isomer has a lower boiling point than an
unbranched isomer There are fewer points of contact when branched chains interact with other
molecules so fewer VDW forces between the molecules
Also branched molecules cannot get as close to each other as unbranched one so fewer
intermolecular forces so less energy required to separate the molecules and lower boiling point
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Short chain alkanes are valuable as clean fuels They burn in a plentiful supply of oxygen to form
carbon dioxide and water
Methane is the main constituent of natural gas and is used for domestic heating and cooking It
burns cleanly in oxygen
CH4(g) + 2O2(g) -----gt CO2(g) + 2H2O(l)
Propane and butane are easily liquefied and are known as liquefied petroleum gas or LPG They are
used as fuels in barbecues patio heaters and portable cooking appliances
Octane is present in petrol used to fuel internal combustion engines
C8H18(g) + 12+
O2(g) -----gt 8CO2(g) + 9H2O(l)
Incomplete Combustion
The internal combustion engine in most cars has a limited supply of oxygen so some of the octane
will undergo incomplete combustion forming carbon monoxide instead of carbon dioxide
C8H18(g) + 8+
O2(g) -----gt 8CO(g) + 9H2O(l)
CO is a colourless odourless gas produced when a fossil fuel is burned with an insufficient supply of
oxygen It is poisonous prevents the haemoglobin in RBCs from binding with oxygen and the bodyrsquos
tissues become starved of oxygen which can be fatal At home CO can be formed form faulty
heating systems blocked chimneys or inadequate ventilation CO detectors protect the home from
the toxic effects of CO
NB In combustion equations C02 molecules = No of carbon atoms in HC and H2O molecules = -
No
Of hydrogen atoms
After fractional distillation there are lots of long-chained hydrocarbons however there is high
demand for short-chained hydrocarbons for use as a) fuels and b)polymer production
Cracking ndash The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-
chained alkanes and alkenes
In catalytic cracking long chained alkanes are broken randomly There are many possible equations
for cracking a particular starting material In catalytic cracking the equations must be balanced and a
mixture of alkanes and alkenes is always formed Most catalytic cracking uses a zeolite catalyst at
450degC
Branched Alkanes can be formed by a process called isomerisation which converts unbranched
alkanes into branched alkanes
Cyclic Hydrocarbons can be produced in a process called reforming where aliphatic hydrocarbons
are converted into cyclic or aromatic hydrocarbons hydrogen is also produced
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Improving Fuels
The Research Octane Number (RON) rates how well a fuel burns Fuels with high octane ratings close
to 100 burn efficiently Heptane (straight-chained alkane) is a poor fuel and has an RON of 0
Branched and cyclic alkanes are important petrol additives they promote more efficient combustion
that straight-chain alkanes Also branched alkanes are used in fuels for car engines
The hydrogen produced during reforming is used in other chemical processes such as ammonia and
margarine production This is a good example of using by-products to make other useful products
We have come to rely on crude oil as a source of power for electrical generation and for transport
Many chemicals produced from crude oil have become important feedstock for the chemical
industry over 90 of crude oil is used for fuel Every day items can be made from petrochemicals
The Earthrsquos deposits of crude oil are depleting at a fast rate
Many of the fuels produced are alkanes Branched and cyclic alkanes are amongst the best fuels A
good fuel needs to be readily available easily transported and inexpensive Oil is suitable but
recently its price has increased significantly and scientists are now looking into alternatives to fossil
fuels
At the start of this century the publicrsquos opinion and concern for the environment has shifted all
hydrocarbons produce pollutants The over reliance on crude oil as for fuel has led environmentalists
to call for urgent actionso it is not only the price of oil that has caused scientists to look for
alternative forms of energy
Burning hydrocarbons leads to an increase in atmospheric pollutants such as
bull Carbon monoxide ndashToxic gas formed by incomplete combustion in internal combustion
engine
bull Carbon dioxide ndash Major contributor o global warming (greenhouse effect)
bull Nitrogen oxides ndash Contributors to acid rain and destruction of forests
bull Sulphur dioxide ndash Acid rain
Global Warming
Refers to an increase in the Earthrsquos average temperature There is growing evidence that this could
be related to human activity such as burning fossil fuels which releases carbon dioxide and other
greenhouse gases into the atmosphere These gases prevent heat from escaping the atmosphere
and leads to increased temperatures on Earth A warmer planet may mean a change in climate with
heavier rain and more frequent violent storms Temperature change also threatens to melt the
polar ice caps which could result in sea levels rising and localised flooding This will have an impact
on all plant and animal forms and will lead to a change in lifestyle
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Fuels for the Future
A biofuel is a fuel that is derived from recently living material such as plants or animal waste
Agricultural crops grown for energy use include sugar cane and rape
Ethanol can be made by fermenting sugar and other carbohydrates It burns efficiently in a plentiful
supply of oxygen to give carbon dioxide and water Ethanol can be blended with petroleum for a fuel
that burns more efficiently Ethanol blends can be used in engines without modifications This
reduces harmful exhaust emissions
Bioethanol is getting a big boost in the UK as the countryrsquos first plants become operational
Biodiesel is a fuel oil derived from natural resources such as plants Rapeseed is the most popular
source in Europe Biodiesel can be used 100 pure in compatible engines however it is normally
blended with normal diesel
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Alkanes react with halogens n the presence of UV radiation or at a temperature of 300degC
This reaction is called Radical Substitution ndash A radical replaces a different atom or group of atoms in
a molecule
bull Covalent bonds are broken by homolytic fission to form radicals
bull A hydrogen atom in the alkane is substituted by a halogen atom
Eg methane reacts with chlorine to produce chloromethane
CH4 + Cl2 -----gt CH3Cl + HCl
Mechanism
Initiation
Cl ndash Cl -----gt Cl + Cl
Propagation
1 CH4+ Cl -----gt CH3 + HCl
2 CH3 + Cl2 -----gt CH3Cl + Cl
Termination
Cl + Cl -----gt Cl2
Cl + CH3 -----gt CH3Cl
CH3 + CH3 -----gt C2H6
Further Reactions of Chloromethane
Other organic products can form in the propagation stage
In the termination stage Chlorine Ethane and chloromethane are formed However chloromethane
may react further with chlorine radicals until all of the hydrogen radicals have been replaced which
results in a mixture of chloromethane dichloromethane trichloromethane and tetrachloromethane
The free radicals are generated
by ultraviolet radiation
The two repeated steps that
build up the products in a chain
reaction Propagations reactions
are rapid and continue until no
reactants remain
Two radicals combine to form a
molecule
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Limitations of Radicals in Synthesis
Every cell in the body produces tens of thousands of radicals every day they are a by-product of cell
metabolism such as form fighting infection or burning glucose for energy they are important in
hormone and enzyme production
Exposure to radicals is linked to premature aging Radicals can damage cell membranes of all cells
and DNA The body has antioxidants that keep radicals in check and protect the body against the
harmful effects of radicals Antioxidants are vitamins C and E We are also exposed to radicals from
cigarette smoke sunbathing pollution and food contaminated with herbicides
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
H
C C
H
H
Alkenes and cycloalkenes are unsaturated hydrocarbons Alkenes have at least one C=C double
bond Aliphatic alkenes with one double bond have the general formula CnH2n They are more
reactive than alkanes and typically take part in addition reactions They can form EZ isomers
including cis-trans isomers
A π-bond is the reactive part of a double bond formed above and below the plane of bonded atoms
by the sideways overlap of p-orbitals Each carbon atom contributes one electron from a p-orbital to
the electron pair in the π-bond which fixes the carbon atoms in position and prevents any rotation
of the bond In alkenes each carbon uses 3 electrons in 3 σ-bonds and 1 electron in one π-bond
Shape of Alkenes
3 regions of electron density surround each carbon atoms in a double bond Pairs of electrons repel
each other as far apart as possible The electron pairs repel each other to give a trigonal planar
shape (120deg)
Cyclic alkenes can be treated the same as branched or straight chained alkenes ndash the react in the
same way
Alkenes are more reactive than alkanes because of the C=C double bond Bond enthalpies show that
a double bond is stronger than a single bond and a π-bond is weaker than a σ-bond When an alkene
breaks the π-bond breaks and the σ-bond stays intact
H
H
C C
H
H
P-orbitals overlap
σ-bond σ-bond
π-bond
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Ni
150degC
C
H
H C
H
H H
H
H
C C
H
H H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
Alkene Reactions
Typically addition reactions
1 A small molecule is added across the double bond causing the π-bond to break
2 2 reactant molecules react together to form on product
3 An unsaturated alkene reacts and forms a saturated alkane
Hydrogenation of Ethene
This is an example of reduction
Halogenation of Ethene
When bromine is added to an alkene sample the colour changes from orange to
colourless The colour change indicates bromine has reacted with the double bond
This is a test for unsaturation it shows the presence of a C=C double bond
Addition of Hydrogen Halides
Hydration of Ethene
A method of preparing alcohols
+ H2
+ Cl2
+ HBr
+ H2O(g) H3PO4
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
C C
H
H H
C
H
H C
H
H H
+
C
H
H C
H
H H
+ C
H
H C
H
H Br
H
Addition of Hydrogen Bromide (electrophilic addition)
+
Hδ+
Brδ-
Br -
Br -
bull In this reaction HBr is
the electrophile
electron pair acceptor
bull HBr is a polar
molecule but non-
polar molecules can
also react with
alkenes
bull The HBr bond breaks
by heterolytic fission
When bromine is added to an
alkene
bull The electrons in the π-
bond repel those in
the Br-Br bond
inducing a dipole in
Br2
bull This forms a
carbocation and a
bromide ion
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
B
C C
A
E D
n C
H
C
H
Cl Cl n
Polymer - A long molecular chain built up from monomer units
Monomer ndash Small molecule that combines with others to form a polymer
If the monomers are alkenes many monomers can be added together to form a long polymer chain
This process is called addition polymerisation
Addition Polymer ndash Very long molecular chain formed by repeated addition reactions of unsaturated
alkene molecules (monomers)
Monomer Polymer (repeated unit)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
The Use of Alkenes
Margarine
The word used for a substance to substitute butter It is made from fats mixed with skimmed milk
and salt Margarine from veg oil is becoming popular for good health people are refusing animal fats
in their diets Margarine with high mono- or polyunsaturated fats are said to be healthier than
butterother margarines Often made from sunflowerolive oil
Veg oils are liquids containing long hydrocarbon chains with many double bonds and are
polyunsaturated The oil must be hardened so it can be spread without being soaked into bread
The oils are hardened by hydrogenation which adds hydrogen molecules across double bonds in an
addition reaction It alters the individual molecule so that the oil partially solidifies and hardens By
adding hydrogen molecules across different numbers of double bonds hardness can vary and
spreadability of margarine can be controlled Partial hydrogenation of unsaturated fats can
transform cis double bonds into trans double bonds as a by-product trans fats are thought to be bad
for health
Poly(phenylethene) Polystyrene is a cheap plastic used in foam packaging insulation model-making
and food retail Polystyrene is being replaced with biodegradable materials as environmental
pressure increases
Poly(propene)Polypropylene is used in food packaging dishwasher safe containers carpet fibres
synthetic ropes It is resistant to chemical attack so is used in certain lab equipment
Addition polymers are durable and do not break down naturally which makes them very useful but
their disposal poses problems
Processing of Waste Polymers
The best way to protect the environment is to re-use polymers without processing
Separation into Types and Recycling
Before plastic waste can be processedconverted it must be sorted Polymer ID codes are used to do
this Optical scanning techniques can separate PET from HDPE bottles Other technologies can
distinguish PVC from other plastics A small quantity of PVC in PET can render the product unsuitable
for re-use PVC is known to release poisonous dioxins when heated
Reclamation
This involves mechanically chopping polymers into small flakes then washing them to remove
impurities The flakes are sent to manufacturing companies where new materials are made by
melting the pellets and remoulding them
PET bottles are converted into carpets clothing and new bottles
HDPE is re-used to make plastic boxes water butts and bins
LDPE waste is made into plastic refuse sacks
Polymers as a Fuel Source
Burning polymers produces heat energy which can be harnessed to generate electricity Agricultural
plastics are being turned into briquettes and are being burned for heat
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
During a chemical reaction bonds are broken in a process called bond fission A covalent
bond can be broken in two ways
bull Homolytic Fission
1 Each bonded atom takes one of the shared pair of electrons
2 Each atom now has an unpaired electron and is called a radical
3 Two species of the same type (lsquohomorsquolytic) are produced
X ndash Y -----gt X + Y
bull Heterolytic Fission
1 One of the bonded atoms takes both of the electrons in the shared pair
2 Two ions are produced
3 The atom that takes both electrons becomes negatively charged (anion)
4 The atom that does not take the shared electron becomes positively charged
(cation)
X ndash Y -----gt X+ + Y-
bull Nucleophile An electron pair donor
bull Electrophile An electron pair acceptor
bull Addition reaction A molecule is added across the double bond of an unsaturated molecule to make a saturated molecule
2 reactants -----gt 1 product
bull Substitution reaction An atom or group of atoms is replaced with a different atom or groups of atoms
2 reactants -----gt 2 products
bull Elimination Reaction The removal of a molecule from a saturated molecule to make a saturated molecule
1 reactant -----gt 2 products
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Percentage Yield
100 yields are rarely achieved possible causes are
bull The reaction may be at equilibrium and may not go to completion
bull Other side reactions may occur leading to by-products
bull The reactants may not be pure
bull Some of the reactants or products may be left behind in the apparatus
bull Separation and purification may result in the loss of some of the product
1313
1313
A Limiting Reagent is the substance in a chemical reaction that runs out first
Atom Economy
A reaction may produce by-products along with the desired product
What can be done with by-products
1 If it is considered to be waste by-products are disposed of This is costly and poses
potential environmental problems
2 By-products may be sold on or used elsewhere in the chemical plant This practice is
likely to increase in the future as we become increasingly concerned about
preserving the earthrsquos resources and minimising waste
Atom economy considers not only the desired product but also the by-products in a chemical
reaction It describes the efficiency of a reaction in terms of all atoms involved High atom economy
means minimal waste
1313 1313
1313
bull Addition reactions 100 atom economy
bull Substitution and Elimination reactions lt 100 atom economy
How can atom economy benefit society
By using products with higher atom economy chemical companies can reduce the amount of waste
produced which is also good for the environment since we a re running out of landfill sites It has
also been suggested that 5-10 of the expenditure of a chemical company goes on waste treatment
bull Percentage yield tells you the efficiency of converting reactants into products
bull Atom economy tells you the proportion of desired products compares with all the products
formed
bull A reaction may have a high percentage yield but a low atom economy
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Hydrocarbons from crude oil
Hydrocarbons are organic compounds containing hydrogen and carbon only
Crude oil is a fossil fuel made from naturally decaying plants and animals that once lived in ancient
seas millions of years ago It is a mixture of over 150 different hydrocarbons most of which are
unbranched Crude oil does not ignite easily so is not useful in its native state However some of its
components are valuable and are used in petrol kerosene and heating and lubricating oils
Fractional Distillation - The separation of the components of crude oil into fractions which differ in
boiling point by means of distillation
Crude oil is refined in a distillation plant
1 The mixture of hydrocarbons is separate into fractions
2 Each fraction consists of a mixture of hydrocarbons with similar boiling points
3 Pure liquids have a fixed boiling point A pure hydrocarbon can be obtained by
further distillation of a crude oil fraction
The process takes place in a fractionating column
A The crude oil is vaporised and then passed into the fractionating column The
column is hotter at the bottom than the top and the gases pass up the column
through a series of bubble caps
B Eventually the gases reach a temperature that is lower than their boiling points
Here the vapour condenses to a liquid The liquid fractions are then tapped off into
storage containers
C Short chained hydrocarbons with lower boiling points condense near the top of the
column
D Longer chained hydrocarbons with higher boiling points condense near the bottom
E Gases which do not condense pass through the top of the column as lsquopetroleum gasrsquo
F The residue from the process is bitumen which is removed from the bottom of the
column
G The fractions obtained from crude oil can be used as fuels or may be further
processed to produce petrochemicals
Alkanes and cycloalkanes are saturated hydrocarbons
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Boiling Points of Alkanes
VDW forces exist between the different alkane molecules in a fraction which have to be broken in
order for the mixture to boil
$ amp ( ) $(
Chain length increases intermolecular forces stronger boiling point increases More points of
contact between long-chained alkanes so more VDW forces It takes more energy and therefore a
higher temperature to separate the molecules
Isomers have the same molecular mass A branched isomer has a lower boiling point than an
unbranched isomer There are fewer points of contact when branched chains interact with other
molecules so fewer VDW forces between the molecules
Also branched molecules cannot get as close to each other as unbranched one so fewer
intermolecular forces so less energy required to separate the molecules and lower boiling point
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Short chain alkanes are valuable as clean fuels They burn in a plentiful supply of oxygen to form
carbon dioxide and water
Methane is the main constituent of natural gas and is used for domestic heating and cooking It
burns cleanly in oxygen
CH4(g) + 2O2(g) -----gt CO2(g) + 2H2O(l)
Propane and butane are easily liquefied and are known as liquefied petroleum gas or LPG They are
used as fuels in barbecues patio heaters and portable cooking appliances
Octane is present in petrol used to fuel internal combustion engines
C8H18(g) + 12+
O2(g) -----gt 8CO2(g) + 9H2O(l)
Incomplete Combustion
The internal combustion engine in most cars has a limited supply of oxygen so some of the octane
will undergo incomplete combustion forming carbon monoxide instead of carbon dioxide
C8H18(g) + 8+
O2(g) -----gt 8CO(g) + 9H2O(l)
CO is a colourless odourless gas produced when a fossil fuel is burned with an insufficient supply of
oxygen It is poisonous prevents the haemoglobin in RBCs from binding with oxygen and the bodyrsquos
tissues become starved of oxygen which can be fatal At home CO can be formed form faulty
heating systems blocked chimneys or inadequate ventilation CO detectors protect the home from
the toxic effects of CO
NB In combustion equations C02 molecules = No of carbon atoms in HC and H2O molecules = -
No
Of hydrogen atoms
After fractional distillation there are lots of long-chained hydrocarbons however there is high
demand for short-chained hydrocarbons for use as a) fuels and b)polymer production
Cracking ndash The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-
chained alkanes and alkenes
In catalytic cracking long chained alkanes are broken randomly There are many possible equations
for cracking a particular starting material In catalytic cracking the equations must be balanced and a
mixture of alkanes and alkenes is always formed Most catalytic cracking uses a zeolite catalyst at
450degC
Branched Alkanes can be formed by a process called isomerisation which converts unbranched
alkanes into branched alkanes
Cyclic Hydrocarbons can be produced in a process called reforming where aliphatic hydrocarbons
are converted into cyclic or aromatic hydrocarbons hydrogen is also produced
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Improving Fuels
The Research Octane Number (RON) rates how well a fuel burns Fuels with high octane ratings close
to 100 burn efficiently Heptane (straight-chained alkane) is a poor fuel and has an RON of 0
Branched and cyclic alkanes are important petrol additives they promote more efficient combustion
that straight-chain alkanes Also branched alkanes are used in fuels for car engines
The hydrogen produced during reforming is used in other chemical processes such as ammonia and
margarine production This is a good example of using by-products to make other useful products
We have come to rely on crude oil as a source of power for electrical generation and for transport
Many chemicals produced from crude oil have become important feedstock for the chemical
industry over 90 of crude oil is used for fuel Every day items can be made from petrochemicals
The Earthrsquos deposits of crude oil are depleting at a fast rate
Many of the fuels produced are alkanes Branched and cyclic alkanes are amongst the best fuels A
good fuel needs to be readily available easily transported and inexpensive Oil is suitable but
recently its price has increased significantly and scientists are now looking into alternatives to fossil
fuels
At the start of this century the publicrsquos opinion and concern for the environment has shifted all
hydrocarbons produce pollutants The over reliance on crude oil as for fuel has led environmentalists
to call for urgent actionso it is not only the price of oil that has caused scientists to look for
alternative forms of energy
Burning hydrocarbons leads to an increase in atmospheric pollutants such as
bull Carbon monoxide ndashToxic gas formed by incomplete combustion in internal combustion
engine
bull Carbon dioxide ndash Major contributor o global warming (greenhouse effect)
bull Nitrogen oxides ndash Contributors to acid rain and destruction of forests
bull Sulphur dioxide ndash Acid rain
Global Warming
Refers to an increase in the Earthrsquos average temperature There is growing evidence that this could
be related to human activity such as burning fossil fuels which releases carbon dioxide and other
greenhouse gases into the atmosphere These gases prevent heat from escaping the atmosphere
and leads to increased temperatures on Earth A warmer planet may mean a change in climate with
heavier rain and more frequent violent storms Temperature change also threatens to melt the
polar ice caps which could result in sea levels rising and localised flooding This will have an impact
on all plant and animal forms and will lead to a change in lifestyle
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Fuels for the Future
A biofuel is a fuel that is derived from recently living material such as plants or animal waste
Agricultural crops grown for energy use include sugar cane and rape
Ethanol can be made by fermenting sugar and other carbohydrates It burns efficiently in a plentiful
supply of oxygen to give carbon dioxide and water Ethanol can be blended with petroleum for a fuel
that burns more efficiently Ethanol blends can be used in engines without modifications This
reduces harmful exhaust emissions
Bioethanol is getting a big boost in the UK as the countryrsquos first plants become operational
Biodiesel is a fuel oil derived from natural resources such as plants Rapeseed is the most popular
source in Europe Biodiesel can be used 100 pure in compatible engines however it is normally
blended with normal diesel
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Alkanes react with halogens n the presence of UV radiation or at a temperature of 300degC
This reaction is called Radical Substitution ndash A radical replaces a different atom or group of atoms in
a molecule
bull Covalent bonds are broken by homolytic fission to form radicals
bull A hydrogen atom in the alkane is substituted by a halogen atom
Eg methane reacts with chlorine to produce chloromethane
CH4 + Cl2 -----gt CH3Cl + HCl
Mechanism
Initiation
Cl ndash Cl -----gt Cl + Cl
Propagation
1 CH4+ Cl -----gt CH3 + HCl
2 CH3 + Cl2 -----gt CH3Cl + Cl
Termination
Cl + Cl -----gt Cl2
Cl + CH3 -----gt CH3Cl
CH3 + CH3 -----gt C2H6
Further Reactions of Chloromethane
Other organic products can form in the propagation stage
In the termination stage Chlorine Ethane and chloromethane are formed However chloromethane
may react further with chlorine radicals until all of the hydrogen radicals have been replaced which
results in a mixture of chloromethane dichloromethane trichloromethane and tetrachloromethane
The free radicals are generated
by ultraviolet radiation
The two repeated steps that
build up the products in a chain
reaction Propagations reactions
are rapid and continue until no
reactants remain
Two radicals combine to form a
molecule
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Limitations of Radicals in Synthesis
Every cell in the body produces tens of thousands of radicals every day they are a by-product of cell
metabolism such as form fighting infection or burning glucose for energy they are important in
hormone and enzyme production
Exposure to radicals is linked to premature aging Radicals can damage cell membranes of all cells
and DNA The body has antioxidants that keep radicals in check and protect the body against the
harmful effects of radicals Antioxidants are vitamins C and E We are also exposed to radicals from
cigarette smoke sunbathing pollution and food contaminated with herbicides
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
H
C C
H
H
Alkenes and cycloalkenes are unsaturated hydrocarbons Alkenes have at least one C=C double
bond Aliphatic alkenes with one double bond have the general formula CnH2n They are more
reactive than alkanes and typically take part in addition reactions They can form EZ isomers
including cis-trans isomers
A π-bond is the reactive part of a double bond formed above and below the plane of bonded atoms
by the sideways overlap of p-orbitals Each carbon atom contributes one electron from a p-orbital to
the electron pair in the π-bond which fixes the carbon atoms in position and prevents any rotation
of the bond In alkenes each carbon uses 3 electrons in 3 σ-bonds and 1 electron in one π-bond
Shape of Alkenes
3 regions of electron density surround each carbon atoms in a double bond Pairs of electrons repel
each other as far apart as possible The electron pairs repel each other to give a trigonal planar
shape (120deg)
Cyclic alkenes can be treated the same as branched or straight chained alkenes ndash the react in the
same way
Alkenes are more reactive than alkanes because of the C=C double bond Bond enthalpies show that
a double bond is stronger than a single bond and a π-bond is weaker than a σ-bond When an alkene
breaks the π-bond breaks and the σ-bond stays intact
H
H
C C
H
H
P-orbitals overlap
σ-bond σ-bond
π-bond
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Ni
150degC
C
H
H C
H
H H
H
H
C C
H
H H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
Alkene Reactions
Typically addition reactions
1 A small molecule is added across the double bond causing the π-bond to break
2 2 reactant molecules react together to form on product
3 An unsaturated alkene reacts and forms a saturated alkane
Hydrogenation of Ethene
This is an example of reduction
Halogenation of Ethene
When bromine is added to an alkene sample the colour changes from orange to
colourless The colour change indicates bromine has reacted with the double bond
This is a test for unsaturation it shows the presence of a C=C double bond
Addition of Hydrogen Halides
Hydration of Ethene
A method of preparing alcohols
+ H2
+ Cl2
+ HBr
+ H2O(g) H3PO4
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
C C
H
H H
C
H
H C
H
H H
+
C
H
H C
H
H H
+ C
H
H C
H
H Br
H
Addition of Hydrogen Bromide (electrophilic addition)
+
Hδ+
Brδ-
Br -
Br -
bull In this reaction HBr is
the electrophile
electron pair acceptor
bull HBr is a polar
molecule but non-
polar molecules can
also react with
alkenes
bull The HBr bond breaks
by heterolytic fission
When bromine is added to an
alkene
bull The electrons in the π-
bond repel those in
the Br-Br bond
inducing a dipole in
Br2
bull This forms a
carbocation and a
bromide ion
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
B
C C
A
E D
n C
H
C
H
Cl Cl n
Polymer - A long molecular chain built up from monomer units
Monomer ndash Small molecule that combines with others to form a polymer
If the monomers are alkenes many monomers can be added together to form a long polymer chain
This process is called addition polymerisation
Addition Polymer ndash Very long molecular chain formed by repeated addition reactions of unsaturated
alkene molecules (monomers)
Monomer Polymer (repeated unit)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
The Use of Alkenes
Margarine
The word used for a substance to substitute butter It is made from fats mixed with skimmed milk
and salt Margarine from veg oil is becoming popular for good health people are refusing animal fats
in their diets Margarine with high mono- or polyunsaturated fats are said to be healthier than
butterother margarines Often made from sunflowerolive oil
Veg oils are liquids containing long hydrocarbon chains with many double bonds and are
polyunsaturated The oil must be hardened so it can be spread without being soaked into bread
The oils are hardened by hydrogenation which adds hydrogen molecules across double bonds in an
addition reaction It alters the individual molecule so that the oil partially solidifies and hardens By
adding hydrogen molecules across different numbers of double bonds hardness can vary and
spreadability of margarine can be controlled Partial hydrogenation of unsaturated fats can
transform cis double bonds into trans double bonds as a by-product trans fats are thought to be bad
for health
Poly(phenylethene) Polystyrene is a cheap plastic used in foam packaging insulation model-making
and food retail Polystyrene is being replaced with biodegradable materials as environmental
pressure increases
Poly(propene)Polypropylene is used in food packaging dishwasher safe containers carpet fibres
synthetic ropes It is resistant to chemical attack so is used in certain lab equipment
Addition polymers are durable and do not break down naturally which makes them very useful but
their disposal poses problems
Processing of Waste Polymers
The best way to protect the environment is to re-use polymers without processing
Separation into Types and Recycling
Before plastic waste can be processedconverted it must be sorted Polymer ID codes are used to do
this Optical scanning techniques can separate PET from HDPE bottles Other technologies can
distinguish PVC from other plastics A small quantity of PVC in PET can render the product unsuitable
for re-use PVC is known to release poisonous dioxins when heated
Reclamation
This involves mechanically chopping polymers into small flakes then washing them to remove
impurities The flakes are sent to manufacturing companies where new materials are made by
melting the pellets and remoulding them
PET bottles are converted into carpets clothing and new bottles
HDPE is re-used to make plastic boxes water butts and bins
LDPE waste is made into plastic refuse sacks
Polymers as a Fuel Source
Burning polymers produces heat energy which can be harnessed to generate electricity Agricultural
plastics are being turned into briquettes and are being burned for heat
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Percentage Yield
100 yields are rarely achieved possible causes are
bull The reaction may be at equilibrium and may not go to completion
bull Other side reactions may occur leading to by-products
bull The reactants may not be pure
bull Some of the reactants or products may be left behind in the apparatus
bull Separation and purification may result in the loss of some of the product
1313
1313
A Limiting Reagent is the substance in a chemical reaction that runs out first
Atom Economy
A reaction may produce by-products along with the desired product
What can be done with by-products
1 If it is considered to be waste by-products are disposed of This is costly and poses
potential environmental problems
2 By-products may be sold on or used elsewhere in the chemical plant This practice is
likely to increase in the future as we become increasingly concerned about
preserving the earthrsquos resources and minimising waste
Atom economy considers not only the desired product but also the by-products in a chemical
reaction It describes the efficiency of a reaction in terms of all atoms involved High atom economy
means minimal waste
1313 1313
1313
bull Addition reactions 100 atom economy
bull Substitution and Elimination reactions lt 100 atom economy
How can atom economy benefit society
By using products with higher atom economy chemical companies can reduce the amount of waste
produced which is also good for the environment since we a re running out of landfill sites It has
also been suggested that 5-10 of the expenditure of a chemical company goes on waste treatment
bull Percentage yield tells you the efficiency of converting reactants into products
bull Atom economy tells you the proportion of desired products compares with all the products
formed
bull A reaction may have a high percentage yield but a low atom economy
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Hydrocarbons from crude oil
Hydrocarbons are organic compounds containing hydrogen and carbon only
Crude oil is a fossil fuel made from naturally decaying plants and animals that once lived in ancient
seas millions of years ago It is a mixture of over 150 different hydrocarbons most of which are
unbranched Crude oil does not ignite easily so is not useful in its native state However some of its
components are valuable and are used in petrol kerosene and heating and lubricating oils
Fractional Distillation - The separation of the components of crude oil into fractions which differ in
boiling point by means of distillation
Crude oil is refined in a distillation plant
1 The mixture of hydrocarbons is separate into fractions
2 Each fraction consists of a mixture of hydrocarbons with similar boiling points
3 Pure liquids have a fixed boiling point A pure hydrocarbon can be obtained by
further distillation of a crude oil fraction
The process takes place in a fractionating column
A The crude oil is vaporised and then passed into the fractionating column The
column is hotter at the bottom than the top and the gases pass up the column
through a series of bubble caps
B Eventually the gases reach a temperature that is lower than their boiling points
Here the vapour condenses to a liquid The liquid fractions are then tapped off into
storage containers
C Short chained hydrocarbons with lower boiling points condense near the top of the
column
D Longer chained hydrocarbons with higher boiling points condense near the bottom
E Gases which do not condense pass through the top of the column as lsquopetroleum gasrsquo
F The residue from the process is bitumen which is removed from the bottom of the
column
G The fractions obtained from crude oil can be used as fuels or may be further
processed to produce petrochemicals
Alkanes and cycloalkanes are saturated hydrocarbons
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Boiling Points of Alkanes
VDW forces exist between the different alkane molecules in a fraction which have to be broken in
order for the mixture to boil
$ amp ( ) $(
Chain length increases intermolecular forces stronger boiling point increases More points of
contact between long-chained alkanes so more VDW forces It takes more energy and therefore a
higher temperature to separate the molecules
Isomers have the same molecular mass A branched isomer has a lower boiling point than an
unbranched isomer There are fewer points of contact when branched chains interact with other
molecules so fewer VDW forces between the molecules
Also branched molecules cannot get as close to each other as unbranched one so fewer
intermolecular forces so less energy required to separate the molecules and lower boiling point
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Short chain alkanes are valuable as clean fuels They burn in a plentiful supply of oxygen to form
carbon dioxide and water
Methane is the main constituent of natural gas and is used for domestic heating and cooking It
burns cleanly in oxygen
CH4(g) + 2O2(g) -----gt CO2(g) + 2H2O(l)
Propane and butane are easily liquefied and are known as liquefied petroleum gas or LPG They are
used as fuels in barbecues patio heaters and portable cooking appliances
Octane is present in petrol used to fuel internal combustion engines
C8H18(g) + 12+
O2(g) -----gt 8CO2(g) + 9H2O(l)
Incomplete Combustion
The internal combustion engine in most cars has a limited supply of oxygen so some of the octane
will undergo incomplete combustion forming carbon monoxide instead of carbon dioxide
C8H18(g) + 8+
O2(g) -----gt 8CO(g) + 9H2O(l)
CO is a colourless odourless gas produced when a fossil fuel is burned with an insufficient supply of
oxygen It is poisonous prevents the haemoglobin in RBCs from binding with oxygen and the bodyrsquos
tissues become starved of oxygen which can be fatal At home CO can be formed form faulty
heating systems blocked chimneys or inadequate ventilation CO detectors protect the home from
the toxic effects of CO
NB In combustion equations C02 molecules = No of carbon atoms in HC and H2O molecules = -
No
Of hydrogen atoms
After fractional distillation there are lots of long-chained hydrocarbons however there is high
demand for short-chained hydrocarbons for use as a) fuels and b)polymer production
Cracking ndash The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-
chained alkanes and alkenes
In catalytic cracking long chained alkanes are broken randomly There are many possible equations
for cracking a particular starting material In catalytic cracking the equations must be balanced and a
mixture of alkanes and alkenes is always formed Most catalytic cracking uses a zeolite catalyst at
450degC
Branched Alkanes can be formed by a process called isomerisation which converts unbranched
alkanes into branched alkanes
Cyclic Hydrocarbons can be produced in a process called reforming where aliphatic hydrocarbons
are converted into cyclic or aromatic hydrocarbons hydrogen is also produced
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Improving Fuels
The Research Octane Number (RON) rates how well a fuel burns Fuels with high octane ratings close
to 100 burn efficiently Heptane (straight-chained alkane) is a poor fuel and has an RON of 0
Branched and cyclic alkanes are important petrol additives they promote more efficient combustion
that straight-chain alkanes Also branched alkanes are used in fuels for car engines
The hydrogen produced during reforming is used in other chemical processes such as ammonia and
margarine production This is a good example of using by-products to make other useful products
We have come to rely on crude oil as a source of power for electrical generation and for transport
Many chemicals produced from crude oil have become important feedstock for the chemical
industry over 90 of crude oil is used for fuel Every day items can be made from petrochemicals
The Earthrsquos deposits of crude oil are depleting at a fast rate
Many of the fuels produced are alkanes Branched and cyclic alkanes are amongst the best fuels A
good fuel needs to be readily available easily transported and inexpensive Oil is suitable but
recently its price has increased significantly and scientists are now looking into alternatives to fossil
fuels
At the start of this century the publicrsquos opinion and concern for the environment has shifted all
hydrocarbons produce pollutants The over reliance on crude oil as for fuel has led environmentalists
to call for urgent actionso it is not only the price of oil that has caused scientists to look for
alternative forms of energy
Burning hydrocarbons leads to an increase in atmospheric pollutants such as
bull Carbon monoxide ndashToxic gas formed by incomplete combustion in internal combustion
engine
bull Carbon dioxide ndash Major contributor o global warming (greenhouse effect)
bull Nitrogen oxides ndash Contributors to acid rain and destruction of forests
bull Sulphur dioxide ndash Acid rain
Global Warming
Refers to an increase in the Earthrsquos average temperature There is growing evidence that this could
be related to human activity such as burning fossil fuels which releases carbon dioxide and other
greenhouse gases into the atmosphere These gases prevent heat from escaping the atmosphere
and leads to increased temperatures on Earth A warmer planet may mean a change in climate with
heavier rain and more frequent violent storms Temperature change also threatens to melt the
polar ice caps which could result in sea levels rising and localised flooding This will have an impact
on all plant and animal forms and will lead to a change in lifestyle
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Fuels for the Future
A biofuel is a fuel that is derived from recently living material such as plants or animal waste
Agricultural crops grown for energy use include sugar cane and rape
Ethanol can be made by fermenting sugar and other carbohydrates It burns efficiently in a plentiful
supply of oxygen to give carbon dioxide and water Ethanol can be blended with petroleum for a fuel
that burns more efficiently Ethanol blends can be used in engines without modifications This
reduces harmful exhaust emissions
Bioethanol is getting a big boost in the UK as the countryrsquos first plants become operational
Biodiesel is a fuel oil derived from natural resources such as plants Rapeseed is the most popular
source in Europe Biodiesel can be used 100 pure in compatible engines however it is normally
blended with normal diesel
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Alkanes react with halogens n the presence of UV radiation or at a temperature of 300degC
This reaction is called Radical Substitution ndash A radical replaces a different atom or group of atoms in
a molecule
bull Covalent bonds are broken by homolytic fission to form radicals
bull A hydrogen atom in the alkane is substituted by a halogen atom
Eg methane reacts with chlorine to produce chloromethane
CH4 + Cl2 -----gt CH3Cl + HCl
Mechanism
Initiation
Cl ndash Cl -----gt Cl + Cl
Propagation
1 CH4+ Cl -----gt CH3 + HCl
2 CH3 + Cl2 -----gt CH3Cl + Cl
Termination
Cl + Cl -----gt Cl2
Cl + CH3 -----gt CH3Cl
CH3 + CH3 -----gt C2H6
Further Reactions of Chloromethane
Other organic products can form in the propagation stage
In the termination stage Chlorine Ethane and chloromethane are formed However chloromethane
may react further with chlorine radicals until all of the hydrogen radicals have been replaced which
results in a mixture of chloromethane dichloromethane trichloromethane and tetrachloromethane
The free radicals are generated
by ultraviolet radiation
The two repeated steps that
build up the products in a chain
reaction Propagations reactions
are rapid and continue until no
reactants remain
Two radicals combine to form a
molecule
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Limitations of Radicals in Synthesis
Every cell in the body produces tens of thousands of radicals every day they are a by-product of cell
metabolism such as form fighting infection or burning glucose for energy they are important in
hormone and enzyme production
Exposure to radicals is linked to premature aging Radicals can damage cell membranes of all cells
and DNA The body has antioxidants that keep radicals in check and protect the body against the
harmful effects of radicals Antioxidants are vitamins C and E We are also exposed to radicals from
cigarette smoke sunbathing pollution and food contaminated with herbicides
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
H
C C
H
H
Alkenes and cycloalkenes are unsaturated hydrocarbons Alkenes have at least one C=C double
bond Aliphatic alkenes with one double bond have the general formula CnH2n They are more
reactive than alkanes and typically take part in addition reactions They can form EZ isomers
including cis-trans isomers
A π-bond is the reactive part of a double bond formed above and below the plane of bonded atoms
by the sideways overlap of p-orbitals Each carbon atom contributes one electron from a p-orbital to
the electron pair in the π-bond which fixes the carbon atoms in position and prevents any rotation
of the bond In alkenes each carbon uses 3 electrons in 3 σ-bonds and 1 electron in one π-bond
Shape of Alkenes
3 regions of electron density surround each carbon atoms in a double bond Pairs of electrons repel
each other as far apart as possible The electron pairs repel each other to give a trigonal planar
shape (120deg)
Cyclic alkenes can be treated the same as branched or straight chained alkenes ndash the react in the
same way
Alkenes are more reactive than alkanes because of the C=C double bond Bond enthalpies show that
a double bond is stronger than a single bond and a π-bond is weaker than a σ-bond When an alkene
breaks the π-bond breaks and the σ-bond stays intact
H
H
C C
H
H
P-orbitals overlap
σ-bond σ-bond
π-bond
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Ni
150degC
C
H
H C
H
H H
H
H
C C
H
H H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
Alkene Reactions
Typically addition reactions
1 A small molecule is added across the double bond causing the π-bond to break
2 2 reactant molecules react together to form on product
3 An unsaturated alkene reacts and forms a saturated alkane
Hydrogenation of Ethene
This is an example of reduction
Halogenation of Ethene
When bromine is added to an alkene sample the colour changes from orange to
colourless The colour change indicates bromine has reacted with the double bond
This is a test for unsaturation it shows the presence of a C=C double bond
Addition of Hydrogen Halides
Hydration of Ethene
A method of preparing alcohols
+ H2
+ Cl2
+ HBr
+ H2O(g) H3PO4
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
C C
H
H H
C
H
H C
H
H H
+
C
H
H C
H
H H
+ C
H
H C
H
H Br
H
Addition of Hydrogen Bromide (electrophilic addition)
+
Hδ+
Brδ-
Br -
Br -
bull In this reaction HBr is
the electrophile
electron pair acceptor
bull HBr is a polar
molecule but non-
polar molecules can
also react with
alkenes
bull The HBr bond breaks
by heterolytic fission
When bromine is added to an
alkene
bull The electrons in the π-
bond repel those in
the Br-Br bond
inducing a dipole in
Br2
bull This forms a
carbocation and a
bromide ion
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
B
C C
A
E D
n C
H
C
H
Cl Cl n
Polymer - A long molecular chain built up from monomer units
Monomer ndash Small molecule that combines with others to form a polymer
If the monomers are alkenes many monomers can be added together to form a long polymer chain
This process is called addition polymerisation
Addition Polymer ndash Very long molecular chain formed by repeated addition reactions of unsaturated
alkene molecules (monomers)
Monomer Polymer (repeated unit)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
The Use of Alkenes
Margarine
The word used for a substance to substitute butter It is made from fats mixed with skimmed milk
and salt Margarine from veg oil is becoming popular for good health people are refusing animal fats
in their diets Margarine with high mono- or polyunsaturated fats are said to be healthier than
butterother margarines Often made from sunflowerolive oil
Veg oils are liquids containing long hydrocarbon chains with many double bonds and are
polyunsaturated The oil must be hardened so it can be spread without being soaked into bread
The oils are hardened by hydrogenation which adds hydrogen molecules across double bonds in an
addition reaction It alters the individual molecule so that the oil partially solidifies and hardens By
adding hydrogen molecules across different numbers of double bonds hardness can vary and
spreadability of margarine can be controlled Partial hydrogenation of unsaturated fats can
transform cis double bonds into trans double bonds as a by-product trans fats are thought to be bad
for health
Poly(phenylethene) Polystyrene is a cheap plastic used in foam packaging insulation model-making
and food retail Polystyrene is being replaced with biodegradable materials as environmental
pressure increases
Poly(propene)Polypropylene is used in food packaging dishwasher safe containers carpet fibres
synthetic ropes It is resistant to chemical attack so is used in certain lab equipment
Addition polymers are durable and do not break down naturally which makes them very useful but
their disposal poses problems
Processing of Waste Polymers
The best way to protect the environment is to re-use polymers without processing
Separation into Types and Recycling
Before plastic waste can be processedconverted it must be sorted Polymer ID codes are used to do
this Optical scanning techniques can separate PET from HDPE bottles Other technologies can
distinguish PVC from other plastics A small quantity of PVC in PET can render the product unsuitable
for re-use PVC is known to release poisonous dioxins when heated
Reclamation
This involves mechanically chopping polymers into small flakes then washing them to remove
impurities The flakes are sent to manufacturing companies where new materials are made by
melting the pellets and remoulding them
PET bottles are converted into carpets clothing and new bottles
HDPE is re-used to make plastic boxes water butts and bins
LDPE waste is made into plastic refuse sacks
Polymers as a Fuel Source
Burning polymers produces heat energy which can be harnessed to generate electricity Agricultural
plastics are being turned into briquettes and are being burned for heat
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Hydrocarbons from crude oil
Hydrocarbons are organic compounds containing hydrogen and carbon only
Crude oil is a fossil fuel made from naturally decaying plants and animals that once lived in ancient
seas millions of years ago It is a mixture of over 150 different hydrocarbons most of which are
unbranched Crude oil does not ignite easily so is not useful in its native state However some of its
components are valuable and are used in petrol kerosene and heating and lubricating oils
Fractional Distillation - The separation of the components of crude oil into fractions which differ in
boiling point by means of distillation
Crude oil is refined in a distillation plant
1 The mixture of hydrocarbons is separate into fractions
2 Each fraction consists of a mixture of hydrocarbons with similar boiling points
3 Pure liquids have a fixed boiling point A pure hydrocarbon can be obtained by
further distillation of a crude oil fraction
The process takes place in a fractionating column
A The crude oil is vaporised and then passed into the fractionating column The
column is hotter at the bottom than the top and the gases pass up the column
through a series of bubble caps
B Eventually the gases reach a temperature that is lower than their boiling points
Here the vapour condenses to a liquid The liquid fractions are then tapped off into
storage containers
C Short chained hydrocarbons with lower boiling points condense near the top of the
column
D Longer chained hydrocarbons with higher boiling points condense near the bottom
E Gases which do not condense pass through the top of the column as lsquopetroleum gasrsquo
F The residue from the process is bitumen which is removed from the bottom of the
column
G The fractions obtained from crude oil can be used as fuels or may be further
processed to produce petrochemicals
Alkanes and cycloalkanes are saturated hydrocarbons
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Boiling Points of Alkanes
VDW forces exist between the different alkane molecules in a fraction which have to be broken in
order for the mixture to boil
$ amp ( ) $(
Chain length increases intermolecular forces stronger boiling point increases More points of
contact between long-chained alkanes so more VDW forces It takes more energy and therefore a
higher temperature to separate the molecules
Isomers have the same molecular mass A branched isomer has a lower boiling point than an
unbranched isomer There are fewer points of contact when branched chains interact with other
molecules so fewer VDW forces between the molecules
Also branched molecules cannot get as close to each other as unbranched one so fewer
intermolecular forces so less energy required to separate the molecules and lower boiling point
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Short chain alkanes are valuable as clean fuels They burn in a plentiful supply of oxygen to form
carbon dioxide and water
Methane is the main constituent of natural gas and is used for domestic heating and cooking It
burns cleanly in oxygen
CH4(g) + 2O2(g) -----gt CO2(g) + 2H2O(l)
Propane and butane are easily liquefied and are known as liquefied petroleum gas or LPG They are
used as fuels in barbecues patio heaters and portable cooking appliances
Octane is present in petrol used to fuel internal combustion engines
C8H18(g) + 12+
O2(g) -----gt 8CO2(g) + 9H2O(l)
Incomplete Combustion
The internal combustion engine in most cars has a limited supply of oxygen so some of the octane
will undergo incomplete combustion forming carbon monoxide instead of carbon dioxide
C8H18(g) + 8+
O2(g) -----gt 8CO(g) + 9H2O(l)
CO is a colourless odourless gas produced when a fossil fuel is burned with an insufficient supply of
oxygen It is poisonous prevents the haemoglobin in RBCs from binding with oxygen and the bodyrsquos
tissues become starved of oxygen which can be fatal At home CO can be formed form faulty
heating systems blocked chimneys or inadequate ventilation CO detectors protect the home from
the toxic effects of CO
NB In combustion equations C02 molecules = No of carbon atoms in HC and H2O molecules = -
No
Of hydrogen atoms
After fractional distillation there are lots of long-chained hydrocarbons however there is high
demand for short-chained hydrocarbons for use as a) fuels and b)polymer production
Cracking ndash The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-
chained alkanes and alkenes
In catalytic cracking long chained alkanes are broken randomly There are many possible equations
for cracking a particular starting material In catalytic cracking the equations must be balanced and a
mixture of alkanes and alkenes is always formed Most catalytic cracking uses a zeolite catalyst at
450degC
Branched Alkanes can be formed by a process called isomerisation which converts unbranched
alkanes into branched alkanes
Cyclic Hydrocarbons can be produced in a process called reforming where aliphatic hydrocarbons
are converted into cyclic or aromatic hydrocarbons hydrogen is also produced
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Improving Fuels
The Research Octane Number (RON) rates how well a fuel burns Fuels with high octane ratings close
to 100 burn efficiently Heptane (straight-chained alkane) is a poor fuel and has an RON of 0
Branched and cyclic alkanes are important petrol additives they promote more efficient combustion
that straight-chain alkanes Also branched alkanes are used in fuels for car engines
The hydrogen produced during reforming is used in other chemical processes such as ammonia and
margarine production This is a good example of using by-products to make other useful products
We have come to rely on crude oil as a source of power for electrical generation and for transport
Many chemicals produced from crude oil have become important feedstock for the chemical
industry over 90 of crude oil is used for fuel Every day items can be made from petrochemicals
The Earthrsquos deposits of crude oil are depleting at a fast rate
Many of the fuels produced are alkanes Branched and cyclic alkanes are amongst the best fuels A
good fuel needs to be readily available easily transported and inexpensive Oil is suitable but
recently its price has increased significantly and scientists are now looking into alternatives to fossil
fuels
At the start of this century the publicrsquos opinion and concern for the environment has shifted all
hydrocarbons produce pollutants The over reliance on crude oil as for fuel has led environmentalists
to call for urgent actionso it is not only the price of oil that has caused scientists to look for
alternative forms of energy
Burning hydrocarbons leads to an increase in atmospheric pollutants such as
bull Carbon monoxide ndashToxic gas formed by incomplete combustion in internal combustion
engine
bull Carbon dioxide ndash Major contributor o global warming (greenhouse effect)
bull Nitrogen oxides ndash Contributors to acid rain and destruction of forests
bull Sulphur dioxide ndash Acid rain
Global Warming
Refers to an increase in the Earthrsquos average temperature There is growing evidence that this could
be related to human activity such as burning fossil fuels which releases carbon dioxide and other
greenhouse gases into the atmosphere These gases prevent heat from escaping the atmosphere
and leads to increased temperatures on Earth A warmer planet may mean a change in climate with
heavier rain and more frequent violent storms Temperature change also threatens to melt the
polar ice caps which could result in sea levels rising and localised flooding This will have an impact
on all plant and animal forms and will lead to a change in lifestyle
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Fuels for the Future
A biofuel is a fuel that is derived from recently living material such as plants or animal waste
Agricultural crops grown for energy use include sugar cane and rape
Ethanol can be made by fermenting sugar and other carbohydrates It burns efficiently in a plentiful
supply of oxygen to give carbon dioxide and water Ethanol can be blended with petroleum for a fuel
that burns more efficiently Ethanol blends can be used in engines without modifications This
reduces harmful exhaust emissions
Bioethanol is getting a big boost in the UK as the countryrsquos first plants become operational
Biodiesel is a fuel oil derived from natural resources such as plants Rapeseed is the most popular
source in Europe Biodiesel can be used 100 pure in compatible engines however it is normally
blended with normal diesel
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Alkanes react with halogens n the presence of UV radiation or at a temperature of 300degC
This reaction is called Radical Substitution ndash A radical replaces a different atom or group of atoms in
a molecule
bull Covalent bonds are broken by homolytic fission to form radicals
bull A hydrogen atom in the alkane is substituted by a halogen atom
Eg methane reacts with chlorine to produce chloromethane
CH4 + Cl2 -----gt CH3Cl + HCl
Mechanism
Initiation
Cl ndash Cl -----gt Cl + Cl
Propagation
1 CH4+ Cl -----gt CH3 + HCl
2 CH3 + Cl2 -----gt CH3Cl + Cl
Termination
Cl + Cl -----gt Cl2
Cl + CH3 -----gt CH3Cl
CH3 + CH3 -----gt C2H6
Further Reactions of Chloromethane
Other organic products can form in the propagation stage
In the termination stage Chlorine Ethane and chloromethane are formed However chloromethane
may react further with chlorine radicals until all of the hydrogen radicals have been replaced which
results in a mixture of chloromethane dichloromethane trichloromethane and tetrachloromethane
The free radicals are generated
by ultraviolet radiation
The two repeated steps that
build up the products in a chain
reaction Propagations reactions
are rapid and continue until no
reactants remain
Two radicals combine to form a
molecule
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Limitations of Radicals in Synthesis
Every cell in the body produces tens of thousands of radicals every day they are a by-product of cell
metabolism such as form fighting infection or burning glucose for energy they are important in
hormone and enzyme production
Exposure to radicals is linked to premature aging Radicals can damage cell membranes of all cells
and DNA The body has antioxidants that keep radicals in check and protect the body against the
harmful effects of radicals Antioxidants are vitamins C and E We are also exposed to radicals from
cigarette smoke sunbathing pollution and food contaminated with herbicides
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
H
C C
H
H
Alkenes and cycloalkenes are unsaturated hydrocarbons Alkenes have at least one C=C double
bond Aliphatic alkenes with one double bond have the general formula CnH2n They are more
reactive than alkanes and typically take part in addition reactions They can form EZ isomers
including cis-trans isomers
A π-bond is the reactive part of a double bond formed above and below the plane of bonded atoms
by the sideways overlap of p-orbitals Each carbon atom contributes one electron from a p-orbital to
the electron pair in the π-bond which fixes the carbon atoms in position and prevents any rotation
of the bond In alkenes each carbon uses 3 electrons in 3 σ-bonds and 1 electron in one π-bond
Shape of Alkenes
3 regions of electron density surround each carbon atoms in a double bond Pairs of electrons repel
each other as far apart as possible The electron pairs repel each other to give a trigonal planar
shape (120deg)
Cyclic alkenes can be treated the same as branched or straight chained alkenes ndash the react in the
same way
Alkenes are more reactive than alkanes because of the C=C double bond Bond enthalpies show that
a double bond is stronger than a single bond and a π-bond is weaker than a σ-bond When an alkene
breaks the π-bond breaks and the σ-bond stays intact
H
H
C C
H
H
P-orbitals overlap
σ-bond σ-bond
π-bond
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Ni
150degC
C
H
H C
H
H H
H
H
C C
H
H H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
Alkene Reactions
Typically addition reactions
1 A small molecule is added across the double bond causing the π-bond to break
2 2 reactant molecules react together to form on product
3 An unsaturated alkene reacts and forms a saturated alkane
Hydrogenation of Ethene
This is an example of reduction
Halogenation of Ethene
When bromine is added to an alkene sample the colour changes from orange to
colourless The colour change indicates bromine has reacted with the double bond
This is a test for unsaturation it shows the presence of a C=C double bond
Addition of Hydrogen Halides
Hydration of Ethene
A method of preparing alcohols
+ H2
+ Cl2
+ HBr
+ H2O(g) H3PO4
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
C C
H
H H
C
H
H C
H
H H
+
C
H
H C
H
H H
+ C
H
H C
H
H Br
H
Addition of Hydrogen Bromide (electrophilic addition)
+
Hδ+
Brδ-
Br -
Br -
bull In this reaction HBr is
the electrophile
electron pair acceptor
bull HBr is a polar
molecule but non-
polar molecules can
also react with
alkenes
bull The HBr bond breaks
by heterolytic fission
When bromine is added to an
alkene
bull The electrons in the π-
bond repel those in
the Br-Br bond
inducing a dipole in
Br2
bull This forms a
carbocation and a
bromide ion
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
B
C C
A
E D
n C
H
C
H
Cl Cl n
Polymer - A long molecular chain built up from monomer units
Monomer ndash Small molecule that combines with others to form a polymer
If the monomers are alkenes many monomers can be added together to form a long polymer chain
This process is called addition polymerisation
Addition Polymer ndash Very long molecular chain formed by repeated addition reactions of unsaturated
alkene molecules (monomers)
Monomer Polymer (repeated unit)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
The Use of Alkenes
Margarine
The word used for a substance to substitute butter It is made from fats mixed with skimmed milk
and salt Margarine from veg oil is becoming popular for good health people are refusing animal fats
in their diets Margarine with high mono- or polyunsaturated fats are said to be healthier than
butterother margarines Often made from sunflowerolive oil
Veg oils are liquids containing long hydrocarbon chains with many double bonds and are
polyunsaturated The oil must be hardened so it can be spread without being soaked into bread
The oils are hardened by hydrogenation which adds hydrogen molecules across double bonds in an
addition reaction It alters the individual molecule so that the oil partially solidifies and hardens By
adding hydrogen molecules across different numbers of double bonds hardness can vary and
spreadability of margarine can be controlled Partial hydrogenation of unsaturated fats can
transform cis double bonds into trans double bonds as a by-product trans fats are thought to be bad
for health
Poly(phenylethene) Polystyrene is a cheap plastic used in foam packaging insulation model-making
and food retail Polystyrene is being replaced with biodegradable materials as environmental
pressure increases
Poly(propene)Polypropylene is used in food packaging dishwasher safe containers carpet fibres
synthetic ropes It is resistant to chemical attack so is used in certain lab equipment
Addition polymers are durable and do not break down naturally which makes them very useful but
their disposal poses problems
Processing of Waste Polymers
The best way to protect the environment is to re-use polymers without processing
Separation into Types and Recycling
Before plastic waste can be processedconverted it must be sorted Polymer ID codes are used to do
this Optical scanning techniques can separate PET from HDPE bottles Other technologies can
distinguish PVC from other plastics A small quantity of PVC in PET can render the product unsuitable
for re-use PVC is known to release poisonous dioxins when heated
Reclamation
This involves mechanically chopping polymers into small flakes then washing them to remove
impurities The flakes are sent to manufacturing companies where new materials are made by
melting the pellets and remoulding them
PET bottles are converted into carpets clothing and new bottles
HDPE is re-used to make plastic boxes water butts and bins
LDPE waste is made into plastic refuse sacks
Polymers as a Fuel Source
Burning polymers produces heat energy which can be harnessed to generate electricity Agricultural
plastics are being turned into briquettes and are being burned for heat
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Boiling Points of Alkanes
VDW forces exist between the different alkane molecules in a fraction which have to be broken in
order for the mixture to boil
$ amp ( ) $(
Chain length increases intermolecular forces stronger boiling point increases More points of
contact between long-chained alkanes so more VDW forces It takes more energy and therefore a
higher temperature to separate the molecules
Isomers have the same molecular mass A branched isomer has a lower boiling point than an
unbranched isomer There are fewer points of contact when branched chains interact with other
molecules so fewer VDW forces between the molecules
Also branched molecules cannot get as close to each other as unbranched one so fewer
intermolecular forces so less energy required to separate the molecules and lower boiling point
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Short chain alkanes are valuable as clean fuels They burn in a plentiful supply of oxygen to form
carbon dioxide and water
Methane is the main constituent of natural gas and is used for domestic heating and cooking It
burns cleanly in oxygen
CH4(g) + 2O2(g) -----gt CO2(g) + 2H2O(l)
Propane and butane are easily liquefied and are known as liquefied petroleum gas or LPG They are
used as fuels in barbecues patio heaters and portable cooking appliances
Octane is present in petrol used to fuel internal combustion engines
C8H18(g) + 12+
O2(g) -----gt 8CO2(g) + 9H2O(l)
Incomplete Combustion
The internal combustion engine in most cars has a limited supply of oxygen so some of the octane
will undergo incomplete combustion forming carbon monoxide instead of carbon dioxide
C8H18(g) + 8+
O2(g) -----gt 8CO(g) + 9H2O(l)
CO is a colourless odourless gas produced when a fossil fuel is burned with an insufficient supply of
oxygen It is poisonous prevents the haemoglobin in RBCs from binding with oxygen and the bodyrsquos
tissues become starved of oxygen which can be fatal At home CO can be formed form faulty
heating systems blocked chimneys or inadequate ventilation CO detectors protect the home from
the toxic effects of CO
NB In combustion equations C02 molecules = No of carbon atoms in HC and H2O molecules = -
No
Of hydrogen atoms
After fractional distillation there are lots of long-chained hydrocarbons however there is high
demand for short-chained hydrocarbons for use as a) fuels and b)polymer production
Cracking ndash The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-
chained alkanes and alkenes
In catalytic cracking long chained alkanes are broken randomly There are many possible equations
for cracking a particular starting material In catalytic cracking the equations must be balanced and a
mixture of alkanes and alkenes is always formed Most catalytic cracking uses a zeolite catalyst at
450degC
Branched Alkanes can be formed by a process called isomerisation which converts unbranched
alkanes into branched alkanes
Cyclic Hydrocarbons can be produced in a process called reforming where aliphatic hydrocarbons
are converted into cyclic or aromatic hydrocarbons hydrogen is also produced
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Improving Fuels
The Research Octane Number (RON) rates how well a fuel burns Fuels with high octane ratings close
to 100 burn efficiently Heptane (straight-chained alkane) is a poor fuel and has an RON of 0
Branched and cyclic alkanes are important petrol additives they promote more efficient combustion
that straight-chain alkanes Also branched alkanes are used in fuels for car engines
The hydrogen produced during reforming is used in other chemical processes such as ammonia and
margarine production This is a good example of using by-products to make other useful products
We have come to rely on crude oil as a source of power for electrical generation and for transport
Many chemicals produced from crude oil have become important feedstock for the chemical
industry over 90 of crude oil is used for fuel Every day items can be made from petrochemicals
The Earthrsquos deposits of crude oil are depleting at a fast rate
Many of the fuels produced are alkanes Branched and cyclic alkanes are amongst the best fuels A
good fuel needs to be readily available easily transported and inexpensive Oil is suitable but
recently its price has increased significantly and scientists are now looking into alternatives to fossil
fuels
At the start of this century the publicrsquos opinion and concern for the environment has shifted all
hydrocarbons produce pollutants The over reliance on crude oil as for fuel has led environmentalists
to call for urgent actionso it is not only the price of oil that has caused scientists to look for
alternative forms of energy
Burning hydrocarbons leads to an increase in atmospheric pollutants such as
bull Carbon monoxide ndashToxic gas formed by incomplete combustion in internal combustion
engine
bull Carbon dioxide ndash Major contributor o global warming (greenhouse effect)
bull Nitrogen oxides ndash Contributors to acid rain and destruction of forests
bull Sulphur dioxide ndash Acid rain
Global Warming
Refers to an increase in the Earthrsquos average temperature There is growing evidence that this could
be related to human activity such as burning fossil fuels which releases carbon dioxide and other
greenhouse gases into the atmosphere These gases prevent heat from escaping the atmosphere
and leads to increased temperatures on Earth A warmer planet may mean a change in climate with
heavier rain and more frequent violent storms Temperature change also threatens to melt the
polar ice caps which could result in sea levels rising and localised flooding This will have an impact
on all plant and animal forms and will lead to a change in lifestyle
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Fuels for the Future
A biofuel is a fuel that is derived from recently living material such as plants or animal waste
Agricultural crops grown for energy use include sugar cane and rape
Ethanol can be made by fermenting sugar and other carbohydrates It burns efficiently in a plentiful
supply of oxygen to give carbon dioxide and water Ethanol can be blended with petroleum for a fuel
that burns more efficiently Ethanol blends can be used in engines without modifications This
reduces harmful exhaust emissions
Bioethanol is getting a big boost in the UK as the countryrsquos first plants become operational
Biodiesel is a fuel oil derived from natural resources such as plants Rapeseed is the most popular
source in Europe Biodiesel can be used 100 pure in compatible engines however it is normally
blended with normal diesel
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Alkanes react with halogens n the presence of UV radiation or at a temperature of 300degC
This reaction is called Radical Substitution ndash A radical replaces a different atom or group of atoms in
a molecule
bull Covalent bonds are broken by homolytic fission to form radicals
bull A hydrogen atom in the alkane is substituted by a halogen atom
Eg methane reacts with chlorine to produce chloromethane
CH4 + Cl2 -----gt CH3Cl + HCl
Mechanism
Initiation
Cl ndash Cl -----gt Cl + Cl
Propagation
1 CH4+ Cl -----gt CH3 + HCl
2 CH3 + Cl2 -----gt CH3Cl + Cl
Termination
Cl + Cl -----gt Cl2
Cl + CH3 -----gt CH3Cl
CH3 + CH3 -----gt C2H6
Further Reactions of Chloromethane
Other organic products can form in the propagation stage
In the termination stage Chlorine Ethane and chloromethane are formed However chloromethane
may react further with chlorine radicals until all of the hydrogen radicals have been replaced which
results in a mixture of chloromethane dichloromethane trichloromethane and tetrachloromethane
The free radicals are generated
by ultraviolet radiation
The two repeated steps that
build up the products in a chain
reaction Propagations reactions
are rapid and continue until no
reactants remain
Two radicals combine to form a
molecule
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Limitations of Radicals in Synthesis
Every cell in the body produces tens of thousands of radicals every day they are a by-product of cell
metabolism such as form fighting infection or burning glucose for energy they are important in
hormone and enzyme production
Exposure to radicals is linked to premature aging Radicals can damage cell membranes of all cells
and DNA The body has antioxidants that keep radicals in check and protect the body against the
harmful effects of radicals Antioxidants are vitamins C and E We are also exposed to radicals from
cigarette smoke sunbathing pollution and food contaminated with herbicides
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
H
C C
H
H
Alkenes and cycloalkenes are unsaturated hydrocarbons Alkenes have at least one C=C double
bond Aliphatic alkenes with one double bond have the general formula CnH2n They are more
reactive than alkanes and typically take part in addition reactions They can form EZ isomers
including cis-trans isomers
A π-bond is the reactive part of a double bond formed above and below the plane of bonded atoms
by the sideways overlap of p-orbitals Each carbon atom contributes one electron from a p-orbital to
the electron pair in the π-bond which fixes the carbon atoms in position and prevents any rotation
of the bond In alkenes each carbon uses 3 electrons in 3 σ-bonds and 1 electron in one π-bond
Shape of Alkenes
3 regions of electron density surround each carbon atoms in a double bond Pairs of electrons repel
each other as far apart as possible The electron pairs repel each other to give a trigonal planar
shape (120deg)
Cyclic alkenes can be treated the same as branched or straight chained alkenes ndash the react in the
same way
Alkenes are more reactive than alkanes because of the C=C double bond Bond enthalpies show that
a double bond is stronger than a single bond and a π-bond is weaker than a σ-bond When an alkene
breaks the π-bond breaks and the σ-bond stays intact
H
H
C C
H
H
P-orbitals overlap
σ-bond σ-bond
π-bond
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Ni
150degC
C
H
H C
H
H H
H
H
C C
H
H H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
Alkene Reactions
Typically addition reactions
1 A small molecule is added across the double bond causing the π-bond to break
2 2 reactant molecules react together to form on product
3 An unsaturated alkene reacts and forms a saturated alkane
Hydrogenation of Ethene
This is an example of reduction
Halogenation of Ethene
When bromine is added to an alkene sample the colour changes from orange to
colourless The colour change indicates bromine has reacted with the double bond
This is a test for unsaturation it shows the presence of a C=C double bond
Addition of Hydrogen Halides
Hydration of Ethene
A method of preparing alcohols
+ H2
+ Cl2
+ HBr
+ H2O(g) H3PO4
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
C C
H
H H
C
H
H C
H
H H
+
C
H
H C
H
H H
+ C
H
H C
H
H Br
H
Addition of Hydrogen Bromide (electrophilic addition)
+
Hδ+
Brδ-
Br -
Br -
bull In this reaction HBr is
the electrophile
electron pair acceptor
bull HBr is a polar
molecule but non-
polar molecules can
also react with
alkenes
bull The HBr bond breaks
by heterolytic fission
When bromine is added to an
alkene
bull The electrons in the π-
bond repel those in
the Br-Br bond
inducing a dipole in
Br2
bull This forms a
carbocation and a
bromide ion
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
B
C C
A
E D
n C
H
C
H
Cl Cl n
Polymer - A long molecular chain built up from monomer units
Monomer ndash Small molecule that combines with others to form a polymer
If the monomers are alkenes many monomers can be added together to form a long polymer chain
This process is called addition polymerisation
Addition Polymer ndash Very long molecular chain formed by repeated addition reactions of unsaturated
alkene molecules (monomers)
Monomer Polymer (repeated unit)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
The Use of Alkenes
Margarine
The word used for a substance to substitute butter It is made from fats mixed with skimmed milk
and salt Margarine from veg oil is becoming popular for good health people are refusing animal fats
in their diets Margarine with high mono- or polyunsaturated fats are said to be healthier than
butterother margarines Often made from sunflowerolive oil
Veg oils are liquids containing long hydrocarbon chains with many double bonds and are
polyunsaturated The oil must be hardened so it can be spread without being soaked into bread
The oils are hardened by hydrogenation which adds hydrogen molecules across double bonds in an
addition reaction It alters the individual molecule so that the oil partially solidifies and hardens By
adding hydrogen molecules across different numbers of double bonds hardness can vary and
spreadability of margarine can be controlled Partial hydrogenation of unsaturated fats can
transform cis double bonds into trans double bonds as a by-product trans fats are thought to be bad
for health
Poly(phenylethene) Polystyrene is a cheap plastic used in foam packaging insulation model-making
and food retail Polystyrene is being replaced with biodegradable materials as environmental
pressure increases
Poly(propene)Polypropylene is used in food packaging dishwasher safe containers carpet fibres
synthetic ropes It is resistant to chemical attack so is used in certain lab equipment
Addition polymers are durable and do not break down naturally which makes them very useful but
their disposal poses problems
Processing of Waste Polymers
The best way to protect the environment is to re-use polymers without processing
Separation into Types and Recycling
Before plastic waste can be processedconverted it must be sorted Polymer ID codes are used to do
this Optical scanning techniques can separate PET from HDPE bottles Other technologies can
distinguish PVC from other plastics A small quantity of PVC in PET can render the product unsuitable
for re-use PVC is known to release poisonous dioxins when heated
Reclamation
This involves mechanically chopping polymers into small flakes then washing them to remove
impurities The flakes are sent to manufacturing companies where new materials are made by
melting the pellets and remoulding them
PET bottles are converted into carpets clothing and new bottles
HDPE is re-used to make plastic boxes water butts and bins
LDPE waste is made into plastic refuse sacks
Polymers as a Fuel Source
Burning polymers produces heat energy which can be harnessed to generate electricity Agricultural
plastics are being turned into briquettes and are being burned for heat
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Short chain alkanes are valuable as clean fuels They burn in a plentiful supply of oxygen to form
carbon dioxide and water
Methane is the main constituent of natural gas and is used for domestic heating and cooking It
burns cleanly in oxygen
CH4(g) + 2O2(g) -----gt CO2(g) + 2H2O(l)
Propane and butane are easily liquefied and are known as liquefied petroleum gas or LPG They are
used as fuels in barbecues patio heaters and portable cooking appliances
Octane is present in petrol used to fuel internal combustion engines
C8H18(g) + 12+
O2(g) -----gt 8CO2(g) + 9H2O(l)
Incomplete Combustion
The internal combustion engine in most cars has a limited supply of oxygen so some of the octane
will undergo incomplete combustion forming carbon monoxide instead of carbon dioxide
C8H18(g) + 8+
O2(g) -----gt 8CO(g) + 9H2O(l)
CO is a colourless odourless gas produced when a fossil fuel is burned with an insufficient supply of
oxygen It is poisonous prevents the haemoglobin in RBCs from binding with oxygen and the bodyrsquos
tissues become starved of oxygen which can be fatal At home CO can be formed form faulty
heating systems blocked chimneys or inadequate ventilation CO detectors protect the home from
the toxic effects of CO
NB In combustion equations C02 molecules = No of carbon atoms in HC and H2O molecules = -
No
Of hydrogen atoms
After fractional distillation there are lots of long-chained hydrocarbons however there is high
demand for short-chained hydrocarbons for use as a) fuels and b)polymer production
Cracking ndash The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-
chained alkanes and alkenes
In catalytic cracking long chained alkanes are broken randomly There are many possible equations
for cracking a particular starting material In catalytic cracking the equations must be balanced and a
mixture of alkanes and alkenes is always formed Most catalytic cracking uses a zeolite catalyst at
450degC
Branched Alkanes can be formed by a process called isomerisation which converts unbranched
alkanes into branched alkanes
Cyclic Hydrocarbons can be produced in a process called reforming where aliphatic hydrocarbons
are converted into cyclic or aromatic hydrocarbons hydrogen is also produced
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Improving Fuels
The Research Octane Number (RON) rates how well a fuel burns Fuels with high octane ratings close
to 100 burn efficiently Heptane (straight-chained alkane) is a poor fuel and has an RON of 0
Branched and cyclic alkanes are important petrol additives they promote more efficient combustion
that straight-chain alkanes Also branched alkanes are used in fuels for car engines
The hydrogen produced during reforming is used in other chemical processes such as ammonia and
margarine production This is a good example of using by-products to make other useful products
We have come to rely on crude oil as a source of power for electrical generation and for transport
Many chemicals produced from crude oil have become important feedstock for the chemical
industry over 90 of crude oil is used for fuel Every day items can be made from petrochemicals
The Earthrsquos deposits of crude oil are depleting at a fast rate
Many of the fuels produced are alkanes Branched and cyclic alkanes are amongst the best fuels A
good fuel needs to be readily available easily transported and inexpensive Oil is suitable but
recently its price has increased significantly and scientists are now looking into alternatives to fossil
fuels
At the start of this century the publicrsquos opinion and concern for the environment has shifted all
hydrocarbons produce pollutants The over reliance on crude oil as for fuel has led environmentalists
to call for urgent actionso it is not only the price of oil that has caused scientists to look for
alternative forms of energy
Burning hydrocarbons leads to an increase in atmospheric pollutants such as
bull Carbon monoxide ndashToxic gas formed by incomplete combustion in internal combustion
engine
bull Carbon dioxide ndash Major contributor o global warming (greenhouse effect)
bull Nitrogen oxides ndash Contributors to acid rain and destruction of forests
bull Sulphur dioxide ndash Acid rain
Global Warming
Refers to an increase in the Earthrsquos average temperature There is growing evidence that this could
be related to human activity such as burning fossil fuels which releases carbon dioxide and other
greenhouse gases into the atmosphere These gases prevent heat from escaping the atmosphere
and leads to increased temperatures on Earth A warmer planet may mean a change in climate with
heavier rain and more frequent violent storms Temperature change also threatens to melt the
polar ice caps which could result in sea levels rising and localised flooding This will have an impact
on all plant and animal forms and will lead to a change in lifestyle
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Fuels for the Future
A biofuel is a fuel that is derived from recently living material such as plants or animal waste
Agricultural crops grown for energy use include sugar cane and rape
Ethanol can be made by fermenting sugar and other carbohydrates It burns efficiently in a plentiful
supply of oxygen to give carbon dioxide and water Ethanol can be blended with petroleum for a fuel
that burns more efficiently Ethanol blends can be used in engines without modifications This
reduces harmful exhaust emissions
Bioethanol is getting a big boost in the UK as the countryrsquos first plants become operational
Biodiesel is a fuel oil derived from natural resources such as plants Rapeseed is the most popular
source in Europe Biodiesel can be used 100 pure in compatible engines however it is normally
blended with normal diesel
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Alkanes react with halogens n the presence of UV radiation or at a temperature of 300degC
This reaction is called Radical Substitution ndash A radical replaces a different atom or group of atoms in
a molecule
bull Covalent bonds are broken by homolytic fission to form radicals
bull A hydrogen atom in the alkane is substituted by a halogen atom
Eg methane reacts with chlorine to produce chloromethane
CH4 + Cl2 -----gt CH3Cl + HCl
Mechanism
Initiation
Cl ndash Cl -----gt Cl + Cl
Propagation
1 CH4+ Cl -----gt CH3 + HCl
2 CH3 + Cl2 -----gt CH3Cl + Cl
Termination
Cl + Cl -----gt Cl2
Cl + CH3 -----gt CH3Cl
CH3 + CH3 -----gt C2H6
Further Reactions of Chloromethane
Other organic products can form in the propagation stage
In the termination stage Chlorine Ethane and chloromethane are formed However chloromethane
may react further with chlorine radicals until all of the hydrogen radicals have been replaced which
results in a mixture of chloromethane dichloromethane trichloromethane and tetrachloromethane
The free radicals are generated
by ultraviolet radiation
The two repeated steps that
build up the products in a chain
reaction Propagations reactions
are rapid and continue until no
reactants remain
Two radicals combine to form a
molecule
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Limitations of Radicals in Synthesis
Every cell in the body produces tens of thousands of radicals every day they are a by-product of cell
metabolism such as form fighting infection or burning glucose for energy they are important in
hormone and enzyme production
Exposure to radicals is linked to premature aging Radicals can damage cell membranes of all cells
and DNA The body has antioxidants that keep radicals in check and protect the body against the
harmful effects of radicals Antioxidants are vitamins C and E We are also exposed to radicals from
cigarette smoke sunbathing pollution and food contaminated with herbicides
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
H
C C
H
H
Alkenes and cycloalkenes are unsaturated hydrocarbons Alkenes have at least one C=C double
bond Aliphatic alkenes with one double bond have the general formula CnH2n They are more
reactive than alkanes and typically take part in addition reactions They can form EZ isomers
including cis-trans isomers
A π-bond is the reactive part of a double bond formed above and below the plane of bonded atoms
by the sideways overlap of p-orbitals Each carbon atom contributes one electron from a p-orbital to
the electron pair in the π-bond which fixes the carbon atoms in position and prevents any rotation
of the bond In alkenes each carbon uses 3 electrons in 3 σ-bonds and 1 electron in one π-bond
Shape of Alkenes
3 regions of electron density surround each carbon atoms in a double bond Pairs of electrons repel
each other as far apart as possible The electron pairs repel each other to give a trigonal planar
shape (120deg)
Cyclic alkenes can be treated the same as branched or straight chained alkenes ndash the react in the
same way
Alkenes are more reactive than alkanes because of the C=C double bond Bond enthalpies show that
a double bond is stronger than a single bond and a π-bond is weaker than a σ-bond When an alkene
breaks the π-bond breaks and the σ-bond stays intact
H
H
C C
H
H
P-orbitals overlap
σ-bond σ-bond
π-bond
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Ni
150degC
C
H
H C
H
H H
H
H
C C
H
H H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
Alkene Reactions
Typically addition reactions
1 A small molecule is added across the double bond causing the π-bond to break
2 2 reactant molecules react together to form on product
3 An unsaturated alkene reacts and forms a saturated alkane
Hydrogenation of Ethene
This is an example of reduction
Halogenation of Ethene
When bromine is added to an alkene sample the colour changes from orange to
colourless The colour change indicates bromine has reacted with the double bond
This is a test for unsaturation it shows the presence of a C=C double bond
Addition of Hydrogen Halides
Hydration of Ethene
A method of preparing alcohols
+ H2
+ Cl2
+ HBr
+ H2O(g) H3PO4
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
C C
H
H H
C
H
H C
H
H H
+
C
H
H C
H
H H
+ C
H
H C
H
H Br
H
Addition of Hydrogen Bromide (electrophilic addition)
+
Hδ+
Brδ-
Br -
Br -
bull In this reaction HBr is
the electrophile
electron pair acceptor
bull HBr is a polar
molecule but non-
polar molecules can
also react with
alkenes
bull The HBr bond breaks
by heterolytic fission
When bromine is added to an
alkene
bull The electrons in the π-
bond repel those in
the Br-Br bond
inducing a dipole in
Br2
bull This forms a
carbocation and a
bromide ion
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
B
C C
A
E D
n C
H
C
H
Cl Cl n
Polymer - A long molecular chain built up from monomer units
Monomer ndash Small molecule that combines with others to form a polymer
If the monomers are alkenes many monomers can be added together to form a long polymer chain
This process is called addition polymerisation
Addition Polymer ndash Very long molecular chain formed by repeated addition reactions of unsaturated
alkene molecules (monomers)
Monomer Polymer (repeated unit)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
The Use of Alkenes
Margarine
The word used for a substance to substitute butter It is made from fats mixed with skimmed milk
and salt Margarine from veg oil is becoming popular for good health people are refusing animal fats
in their diets Margarine with high mono- or polyunsaturated fats are said to be healthier than
butterother margarines Often made from sunflowerolive oil
Veg oils are liquids containing long hydrocarbon chains with many double bonds and are
polyunsaturated The oil must be hardened so it can be spread without being soaked into bread
The oils are hardened by hydrogenation which adds hydrogen molecules across double bonds in an
addition reaction It alters the individual molecule so that the oil partially solidifies and hardens By
adding hydrogen molecules across different numbers of double bonds hardness can vary and
spreadability of margarine can be controlled Partial hydrogenation of unsaturated fats can
transform cis double bonds into trans double bonds as a by-product trans fats are thought to be bad
for health
Poly(phenylethene) Polystyrene is a cheap plastic used in foam packaging insulation model-making
and food retail Polystyrene is being replaced with biodegradable materials as environmental
pressure increases
Poly(propene)Polypropylene is used in food packaging dishwasher safe containers carpet fibres
synthetic ropes It is resistant to chemical attack so is used in certain lab equipment
Addition polymers are durable and do not break down naturally which makes them very useful but
their disposal poses problems
Processing of Waste Polymers
The best way to protect the environment is to re-use polymers without processing
Separation into Types and Recycling
Before plastic waste can be processedconverted it must be sorted Polymer ID codes are used to do
this Optical scanning techniques can separate PET from HDPE bottles Other technologies can
distinguish PVC from other plastics A small quantity of PVC in PET can render the product unsuitable
for re-use PVC is known to release poisonous dioxins when heated
Reclamation
This involves mechanically chopping polymers into small flakes then washing them to remove
impurities The flakes are sent to manufacturing companies where new materials are made by
melting the pellets and remoulding them
PET bottles are converted into carpets clothing and new bottles
HDPE is re-used to make plastic boxes water butts and bins
LDPE waste is made into plastic refuse sacks
Polymers as a Fuel Source
Burning polymers produces heat energy which can be harnessed to generate electricity Agricultural
plastics are being turned into briquettes and are being burned for heat
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Improving Fuels
The Research Octane Number (RON) rates how well a fuel burns Fuels with high octane ratings close
to 100 burn efficiently Heptane (straight-chained alkane) is a poor fuel and has an RON of 0
Branched and cyclic alkanes are important petrol additives they promote more efficient combustion
that straight-chain alkanes Also branched alkanes are used in fuels for car engines
The hydrogen produced during reforming is used in other chemical processes such as ammonia and
margarine production This is a good example of using by-products to make other useful products
We have come to rely on crude oil as a source of power for electrical generation and for transport
Many chemicals produced from crude oil have become important feedstock for the chemical
industry over 90 of crude oil is used for fuel Every day items can be made from petrochemicals
The Earthrsquos deposits of crude oil are depleting at a fast rate
Many of the fuels produced are alkanes Branched and cyclic alkanes are amongst the best fuels A
good fuel needs to be readily available easily transported and inexpensive Oil is suitable but
recently its price has increased significantly and scientists are now looking into alternatives to fossil
fuels
At the start of this century the publicrsquos opinion and concern for the environment has shifted all
hydrocarbons produce pollutants The over reliance on crude oil as for fuel has led environmentalists
to call for urgent actionso it is not only the price of oil that has caused scientists to look for
alternative forms of energy
Burning hydrocarbons leads to an increase in atmospheric pollutants such as
bull Carbon monoxide ndashToxic gas formed by incomplete combustion in internal combustion
engine
bull Carbon dioxide ndash Major contributor o global warming (greenhouse effect)
bull Nitrogen oxides ndash Contributors to acid rain and destruction of forests
bull Sulphur dioxide ndash Acid rain
Global Warming
Refers to an increase in the Earthrsquos average temperature There is growing evidence that this could
be related to human activity such as burning fossil fuels which releases carbon dioxide and other
greenhouse gases into the atmosphere These gases prevent heat from escaping the atmosphere
and leads to increased temperatures on Earth A warmer planet may mean a change in climate with
heavier rain and more frequent violent storms Temperature change also threatens to melt the
polar ice caps which could result in sea levels rising and localised flooding This will have an impact
on all plant and animal forms and will lead to a change in lifestyle
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Fuels for the Future
A biofuel is a fuel that is derived from recently living material such as plants or animal waste
Agricultural crops grown for energy use include sugar cane and rape
Ethanol can be made by fermenting sugar and other carbohydrates It burns efficiently in a plentiful
supply of oxygen to give carbon dioxide and water Ethanol can be blended with petroleum for a fuel
that burns more efficiently Ethanol blends can be used in engines without modifications This
reduces harmful exhaust emissions
Bioethanol is getting a big boost in the UK as the countryrsquos first plants become operational
Biodiesel is a fuel oil derived from natural resources such as plants Rapeseed is the most popular
source in Europe Biodiesel can be used 100 pure in compatible engines however it is normally
blended with normal diesel
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Alkanes react with halogens n the presence of UV radiation or at a temperature of 300degC
This reaction is called Radical Substitution ndash A radical replaces a different atom or group of atoms in
a molecule
bull Covalent bonds are broken by homolytic fission to form radicals
bull A hydrogen atom in the alkane is substituted by a halogen atom
Eg methane reacts with chlorine to produce chloromethane
CH4 + Cl2 -----gt CH3Cl + HCl
Mechanism
Initiation
Cl ndash Cl -----gt Cl + Cl
Propagation
1 CH4+ Cl -----gt CH3 + HCl
2 CH3 + Cl2 -----gt CH3Cl + Cl
Termination
Cl + Cl -----gt Cl2
Cl + CH3 -----gt CH3Cl
CH3 + CH3 -----gt C2H6
Further Reactions of Chloromethane
Other organic products can form in the propagation stage
In the termination stage Chlorine Ethane and chloromethane are formed However chloromethane
may react further with chlorine radicals until all of the hydrogen radicals have been replaced which
results in a mixture of chloromethane dichloromethane trichloromethane and tetrachloromethane
The free radicals are generated
by ultraviolet radiation
The two repeated steps that
build up the products in a chain
reaction Propagations reactions
are rapid and continue until no
reactants remain
Two radicals combine to form a
molecule
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Limitations of Radicals in Synthesis
Every cell in the body produces tens of thousands of radicals every day they are a by-product of cell
metabolism such as form fighting infection or burning glucose for energy they are important in
hormone and enzyme production
Exposure to radicals is linked to premature aging Radicals can damage cell membranes of all cells
and DNA The body has antioxidants that keep radicals in check and protect the body against the
harmful effects of radicals Antioxidants are vitamins C and E We are also exposed to radicals from
cigarette smoke sunbathing pollution and food contaminated with herbicides
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
H
C C
H
H
Alkenes and cycloalkenes are unsaturated hydrocarbons Alkenes have at least one C=C double
bond Aliphatic alkenes with one double bond have the general formula CnH2n They are more
reactive than alkanes and typically take part in addition reactions They can form EZ isomers
including cis-trans isomers
A π-bond is the reactive part of a double bond formed above and below the plane of bonded atoms
by the sideways overlap of p-orbitals Each carbon atom contributes one electron from a p-orbital to
the electron pair in the π-bond which fixes the carbon atoms in position and prevents any rotation
of the bond In alkenes each carbon uses 3 electrons in 3 σ-bonds and 1 electron in one π-bond
Shape of Alkenes
3 regions of electron density surround each carbon atoms in a double bond Pairs of electrons repel
each other as far apart as possible The electron pairs repel each other to give a trigonal planar
shape (120deg)
Cyclic alkenes can be treated the same as branched or straight chained alkenes ndash the react in the
same way
Alkenes are more reactive than alkanes because of the C=C double bond Bond enthalpies show that
a double bond is stronger than a single bond and a π-bond is weaker than a σ-bond When an alkene
breaks the π-bond breaks and the σ-bond stays intact
H
H
C C
H
H
P-orbitals overlap
σ-bond σ-bond
π-bond
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Ni
150degC
C
H
H C
H
H H
H
H
C C
H
H H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
Alkene Reactions
Typically addition reactions
1 A small molecule is added across the double bond causing the π-bond to break
2 2 reactant molecules react together to form on product
3 An unsaturated alkene reacts and forms a saturated alkane
Hydrogenation of Ethene
This is an example of reduction
Halogenation of Ethene
When bromine is added to an alkene sample the colour changes from orange to
colourless The colour change indicates bromine has reacted with the double bond
This is a test for unsaturation it shows the presence of a C=C double bond
Addition of Hydrogen Halides
Hydration of Ethene
A method of preparing alcohols
+ H2
+ Cl2
+ HBr
+ H2O(g) H3PO4
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
C C
H
H H
C
H
H C
H
H H
+
C
H
H C
H
H H
+ C
H
H C
H
H Br
H
Addition of Hydrogen Bromide (electrophilic addition)
+
Hδ+
Brδ-
Br -
Br -
bull In this reaction HBr is
the electrophile
electron pair acceptor
bull HBr is a polar
molecule but non-
polar molecules can
also react with
alkenes
bull The HBr bond breaks
by heterolytic fission
When bromine is added to an
alkene
bull The electrons in the π-
bond repel those in
the Br-Br bond
inducing a dipole in
Br2
bull This forms a
carbocation and a
bromide ion
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
B
C C
A
E D
n C
H
C
H
Cl Cl n
Polymer - A long molecular chain built up from monomer units
Monomer ndash Small molecule that combines with others to form a polymer
If the monomers are alkenes many monomers can be added together to form a long polymer chain
This process is called addition polymerisation
Addition Polymer ndash Very long molecular chain formed by repeated addition reactions of unsaturated
alkene molecules (monomers)
Monomer Polymer (repeated unit)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
The Use of Alkenes
Margarine
The word used for a substance to substitute butter It is made from fats mixed with skimmed milk
and salt Margarine from veg oil is becoming popular for good health people are refusing animal fats
in their diets Margarine with high mono- or polyunsaturated fats are said to be healthier than
butterother margarines Often made from sunflowerolive oil
Veg oils are liquids containing long hydrocarbon chains with many double bonds and are
polyunsaturated The oil must be hardened so it can be spread without being soaked into bread
The oils are hardened by hydrogenation which adds hydrogen molecules across double bonds in an
addition reaction It alters the individual molecule so that the oil partially solidifies and hardens By
adding hydrogen molecules across different numbers of double bonds hardness can vary and
spreadability of margarine can be controlled Partial hydrogenation of unsaturated fats can
transform cis double bonds into trans double bonds as a by-product trans fats are thought to be bad
for health
Poly(phenylethene) Polystyrene is a cheap plastic used in foam packaging insulation model-making
and food retail Polystyrene is being replaced with biodegradable materials as environmental
pressure increases
Poly(propene)Polypropylene is used in food packaging dishwasher safe containers carpet fibres
synthetic ropes It is resistant to chemical attack so is used in certain lab equipment
Addition polymers are durable and do not break down naturally which makes them very useful but
their disposal poses problems
Processing of Waste Polymers
The best way to protect the environment is to re-use polymers without processing
Separation into Types and Recycling
Before plastic waste can be processedconverted it must be sorted Polymer ID codes are used to do
this Optical scanning techniques can separate PET from HDPE bottles Other technologies can
distinguish PVC from other plastics A small quantity of PVC in PET can render the product unsuitable
for re-use PVC is known to release poisonous dioxins when heated
Reclamation
This involves mechanically chopping polymers into small flakes then washing them to remove
impurities The flakes are sent to manufacturing companies where new materials are made by
melting the pellets and remoulding them
PET bottles are converted into carpets clothing and new bottles
HDPE is re-used to make plastic boxes water butts and bins
LDPE waste is made into plastic refuse sacks
Polymers as a Fuel Source
Burning polymers produces heat energy which can be harnessed to generate electricity Agricultural
plastics are being turned into briquettes and are being burned for heat
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Fuels for the Future
A biofuel is a fuel that is derived from recently living material such as plants or animal waste
Agricultural crops grown for energy use include sugar cane and rape
Ethanol can be made by fermenting sugar and other carbohydrates It burns efficiently in a plentiful
supply of oxygen to give carbon dioxide and water Ethanol can be blended with petroleum for a fuel
that burns more efficiently Ethanol blends can be used in engines without modifications This
reduces harmful exhaust emissions
Bioethanol is getting a big boost in the UK as the countryrsquos first plants become operational
Biodiesel is a fuel oil derived from natural resources such as plants Rapeseed is the most popular
source in Europe Biodiesel can be used 100 pure in compatible engines however it is normally
blended with normal diesel
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Alkanes react with halogens n the presence of UV radiation or at a temperature of 300degC
This reaction is called Radical Substitution ndash A radical replaces a different atom or group of atoms in
a molecule
bull Covalent bonds are broken by homolytic fission to form radicals
bull A hydrogen atom in the alkane is substituted by a halogen atom
Eg methane reacts with chlorine to produce chloromethane
CH4 + Cl2 -----gt CH3Cl + HCl
Mechanism
Initiation
Cl ndash Cl -----gt Cl + Cl
Propagation
1 CH4+ Cl -----gt CH3 + HCl
2 CH3 + Cl2 -----gt CH3Cl + Cl
Termination
Cl + Cl -----gt Cl2
Cl + CH3 -----gt CH3Cl
CH3 + CH3 -----gt C2H6
Further Reactions of Chloromethane
Other organic products can form in the propagation stage
In the termination stage Chlorine Ethane and chloromethane are formed However chloromethane
may react further with chlorine radicals until all of the hydrogen radicals have been replaced which
results in a mixture of chloromethane dichloromethane trichloromethane and tetrachloromethane
The free radicals are generated
by ultraviolet radiation
The two repeated steps that
build up the products in a chain
reaction Propagations reactions
are rapid and continue until no
reactants remain
Two radicals combine to form a
molecule
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Limitations of Radicals in Synthesis
Every cell in the body produces tens of thousands of radicals every day they are a by-product of cell
metabolism such as form fighting infection or burning glucose for energy they are important in
hormone and enzyme production
Exposure to radicals is linked to premature aging Radicals can damage cell membranes of all cells
and DNA The body has antioxidants that keep radicals in check and protect the body against the
harmful effects of radicals Antioxidants are vitamins C and E We are also exposed to radicals from
cigarette smoke sunbathing pollution and food contaminated with herbicides
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
H
C C
H
H
Alkenes and cycloalkenes are unsaturated hydrocarbons Alkenes have at least one C=C double
bond Aliphatic alkenes with one double bond have the general formula CnH2n They are more
reactive than alkanes and typically take part in addition reactions They can form EZ isomers
including cis-trans isomers
A π-bond is the reactive part of a double bond formed above and below the plane of bonded atoms
by the sideways overlap of p-orbitals Each carbon atom contributes one electron from a p-orbital to
the electron pair in the π-bond which fixes the carbon atoms in position and prevents any rotation
of the bond In alkenes each carbon uses 3 electrons in 3 σ-bonds and 1 electron in one π-bond
Shape of Alkenes
3 regions of electron density surround each carbon atoms in a double bond Pairs of electrons repel
each other as far apart as possible The electron pairs repel each other to give a trigonal planar
shape (120deg)
Cyclic alkenes can be treated the same as branched or straight chained alkenes ndash the react in the
same way
Alkenes are more reactive than alkanes because of the C=C double bond Bond enthalpies show that
a double bond is stronger than a single bond and a π-bond is weaker than a σ-bond When an alkene
breaks the π-bond breaks and the σ-bond stays intact
H
H
C C
H
H
P-orbitals overlap
σ-bond σ-bond
π-bond
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Ni
150degC
C
H
H C
H
H H
H
H
C C
H
H H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
Alkene Reactions
Typically addition reactions
1 A small molecule is added across the double bond causing the π-bond to break
2 2 reactant molecules react together to form on product
3 An unsaturated alkene reacts and forms a saturated alkane
Hydrogenation of Ethene
This is an example of reduction
Halogenation of Ethene
When bromine is added to an alkene sample the colour changes from orange to
colourless The colour change indicates bromine has reacted with the double bond
This is a test for unsaturation it shows the presence of a C=C double bond
Addition of Hydrogen Halides
Hydration of Ethene
A method of preparing alcohols
+ H2
+ Cl2
+ HBr
+ H2O(g) H3PO4
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
C C
H
H H
C
H
H C
H
H H
+
C
H
H C
H
H H
+ C
H
H C
H
H Br
H
Addition of Hydrogen Bromide (electrophilic addition)
+
Hδ+
Brδ-
Br -
Br -
bull In this reaction HBr is
the electrophile
electron pair acceptor
bull HBr is a polar
molecule but non-
polar molecules can
also react with
alkenes
bull The HBr bond breaks
by heterolytic fission
When bromine is added to an
alkene
bull The electrons in the π-
bond repel those in
the Br-Br bond
inducing a dipole in
Br2
bull This forms a
carbocation and a
bromide ion
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
B
C C
A
E D
n C
H
C
H
Cl Cl n
Polymer - A long molecular chain built up from monomer units
Monomer ndash Small molecule that combines with others to form a polymer
If the monomers are alkenes many monomers can be added together to form a long polymer chain
This process is called addition polymerisation
Addition Polymer ndash Very long molecular chain formed by repeated addition reactions of unsaturated
alkene molecules (monomers)
Monomer Polymer (repeated unit)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
The Use of Alkenes
Margarine
The word used for a substance to substitute butter It is made from fats mixed with skimmed milk
and salt Margarine from veg oil is becoming popular for good health people are refusing animal fats
in their diets Margarine with high mono- or polyunsaturated fats are said to be healthier than
butterother margarines Often made from sunflowerolive oil
Veg oils are liquids containing long hydrocarbon chains with many double bonds and are
polyunsaturated The oil must be hardened so it can be spread without being soaked into bread
The oils are hardened by hydrogenation which adds hydrogen molecules across double bonds in an
addition reaction It alters the individual molecule so that the oil partially solidifies and hardens By
adding hydrogen molecules across different numbers of double bonds hardness can vary and
spreadability of margarine can be controlled Partial hydrogenation of unsaturated fats can
transform cis double bonds into trans double bonds as a by-product trans fats are thought to be bad
for health
Poly(phenylethene) Polystyrene is a cheap plastic used in foam packaging insulation model-making
and food retail Polystyrene is being replaced with biodegradable materials as environmental
pressure increases
Poly(propene)Polypropylene is used in food packaging dishwasher safe containers carpet fibres
synthetic ropes It is resistant to chemical attack so is used in certain lab equipment
Addition polymers are durable and do not break down naturally which makes them very useful but
their disposal poses problems
Processing of Waste Polymers
The best way to protect the environment is to re-use polymers without processing
Separation into Types and Recycling
Before plastic waste can be processedconverted it must be sorted Polymer ID codes are used to do
this Optical scanning techniques can separate PET from HDPE bottles Other technologies can
distinguish PVC from other plastics A small quantity of PVC in PET can render the product unsuitable
for re-use PVC is known to release poisonous dioxins when heated
Reclamation
This involves mechanically chopping polymers into small flakes then washing them to remove
impurities The flakes are sent to manufacturing companies where new materials are made by
melting the pellets and remoulding them
PET bottles are converted into carpets clothing and new bottles
HDPE is re-used to make plastic boxes water butts and bins
LDPE waste is made into plastic refuse sacks
Polymers as a Fuel Source
Burning polymers produces heat energy which can be harnessed to generate electricity Agricultural
plastics are being turned into briquettes and are being burned for heat
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Alkanes react with halogens n the presence of UV radiation or at a temperature of 300degC
This reaction is called Radical Substitution ndash A radical replaces a different atom or group of atoms in
a molecule
bull Covalent bonds are broken by homolytic fission to form radicals
bull A hydrogen atom in the alkane is substituted by a halogen atom
Eg methane reacts with chlorine to produce chloromethane
CH4 + Cl2 -----gt CH3Cl + HCl
Mechanism
Initiation
Cl ndash Cl -----gt Cl + Cl
Propagation
1 CH4+ Cl -----gt CH3 + HCl
2 CH3 + Cl2 -----gt CH3Cl + Cl
Termination
Cl + Cl -----gt Cl2
Cl + CH3 -----gt CH3Cl
CH3 + CH3 -----gt C2H6
Further Reactions of Chloromethane
Other organic products can form in the propagation stage
In the termination stage Chlorine Ethane and chloromethane are formed However chloromethane
may react further with chlorine radicals until all of the hydrogen radicals have been replaced which
results in a mixture of chloromethane dichloromethane trichloromethane and tetrachloromethane
The free radicals are generated
by ultraviolet radiation
The two repeated steps that
build up the products in a chain
reaction Propagations reactions
are rapid and continue until no
reactants remain
Two radicals combine to form a
molecule
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Limitations of Radicals in Synthesis
Every cell in the body produces tens of thousands of radicals every day they are a by-product of cell
metabolism such as form fighting infection or burning glucose for energy they are important in
hormone and enzyme production
Exposure to radicals is linked to premature aging Radicals can damage cell membranes of all cells
and DNA The body has antioxidants that keep radicals in check and protect the body against the
harmful effects of radicals Antioxidants are vitamins C and E We are also exposed to radicals from
cigarette smoke sunbathing pollution and food contaminated with herbicides
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
H
C C
H
H
Alkenes and cycloalkenes are unsaturated hydrocarbons Alkenes have at least one C=C double
bond Aliphatic alkenes with one double bond have the general formula CnH2n They are more
reactive than alkanes and typically take part in addition reactions They can form EZ isomers
including cis-trans isomers
A π-bond is the reactive part of a double bond formed above and below the plane of bonded atoms
by the sideways overlap of p-orbitals Each carbon atom contributes one electron from a p-orbital to
the electron pair in the π-bond which fixes the carbon atoms in position and prevents any rotation
of the bond In alkenes each carbon uses 3 electrons in 3 σ-bonds and 1 electron in one π-bond
Shape of Alkenes
3 regions of electron density surround each carbon atoms in a double bond Pairs of electrons repel
each other as far apart as possible The electron pairs repel each other to give a trigonal planar
shape (120deg)
Cyclic alkenes can be treated the same as branched or straight chained alkenes ndash the react in the
same way
Alkenes are more reactive than alkanes because of the C=C double bond Bond enthalpies show that
a double bond is stronger than a single bond and a π-bond is weaker than a σ-bond When an alkene
breaks the π-bond breaks and the σ-bond stays intact
H
H
C C
H
H
P-orbitals overlap
σ-bond σ-bond
π-bond
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Ni
150degC
C
H
H C
H
H H
H
H
C C
H
H H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
Alkene Reactions
Typically addition reactions
1 A small molecule is added across the double bond causing the π-bond to break
2 2 reactant molecules react together to form on product
3 An unsaturated alkene reacts and forms a saturated alkane
Hydrogenation of Ethene
This is an example of reduction
Halogenation of Ethene
When bromine is added to an alkene sample the colour changes from orange to
colourless The colour change indicates bromine has reacted with the double bond
This is a test for unsaturation it shows the presence of a C=C double bond
Addition of Hydrogen Halides
Hydration of Ethene
A method of preparing alcohols
+ H2
+ Cl2
+ HBr
+ H2O(g) H3PO4
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
C C
H
H H
C
H
H C
H
H H
+
C
H
H C
H
H H
+ C
H
H C
H
H Br
H
Addition of Hydrogen Bromide (electrophilic addition)
+
Hδ+
Brδ-
Br -
Br -
bull In this reaction HBr is
the electrophile
electron pair acceptor
bull HBr is a polar
molecule but non-
polar molecules can
also react with
alkenes
bull The HBr bond breaks
by heterolytic fission
When bromine is added to an
alkene
bull The electrons in the π-
bond repel those in
the Br-Br bond
inducing a dipole in
Br2
bull This forms a
carbocation and a
bromide ion
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
B
C C
A
E D
n C
H
C
H
Cl Cl n
Polymer - A long molecular chain built up from monomer units
Monomer ndash Small molecule that combines with others to form a polymer
If the monomers are alkenes many monomers can be added together to form a long polymer chain
This process is called addition polymerisation
Addition Polymer ndash Very long molecular chain formed by repeated addition reactions of unsaturated
alkene molecules (monomers)
Monomer Polymer (repeated unit)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
The Use of Alkenes
Margarine
The word used for a substance to substitute butter It is made from fats mixed with skimmed milk
and salt Margarine from veg oil is becoming popular for good health people are refusing animal fats
in their diets Margarine with high mono- or polyunsaturated fats are said to be healthier than
butterother margarines Often made from sunflowerolive oil
Veg oils are liquids containing long hydrocarbon chains with many double bonds and are
polyunsaturated The oil must be hardened so it can be spread without being soaked into bread
The oils are hardened by hydrogenation which adds hydrogen molecules across double bonds in an
addition reaction It alters the individual molecule so that the oil partially solidifies and hardens By
adding hydrogen molecules across different numbers of double bonds hardness can vary and
spreadability of margarine can be controlled Partial hydrogenation of unsaturated fats can
transform cis double bonds into trans double bonds as a by-product trans fats are thought to be bad
for health
Poly(phenylethene) Polystyrene is a cheap plastic used in foam packaging insulation model-making
and food retail Polystyrene is being replaced with biodegradable materials as environmental
pressure increases
Poly(propene)Polypropylene is used in food packaging dishwasher safe containers carpet fibres
synthetic ropes It is resistant to chemical attack so is used in certain lab equipment
Addition polymers are durable and do not break down naturally which makes them very useful but
their disposal poses problems
Processing of Waste Polymers
The best way to protect the environment is to re-use polymers without processing
Separation into Types and Recycling
Before plastic waste can be processedconverted it must be sorted Polymer ID codes are used to do
this Optical scanning techniques can separate PET from HDPE bottles Other technologies can
distinguish PVC from other plastics A small quantity of PVC in PET can render the product unsuitable
for re-use PVC is known to release poisonous dioxins when heated
Reclamation
This involves mechanically chopping polymers into small flakes then washing them to remove
impurities The flakes are sent to manufacturing companies where new materials are made by
melting the pellets and remoulding them
PET bottles are converted into carpets clothing and new bottles
HDPE is re-used to make plastic boxes water butts and bins
LDPE waste is made into plastic refuse sacks
Polymers as a Fuel Source
Burning polymers produces heat energy which can be harnessed to generate electricity Agricultural
plastics are being turned into briquettes and are being burned for heat
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Limitations of Radicals in Synthesis
Every cell in the body produces tens of thousands of radicals every day they are a by-product of cell
metabolism such as form fighting infection or burning glucose for energy they are important in
hormone and enzyme production
Exposure to radicals is linked to premature aging Radicals can damage cell membranes of all cells
and DNA The body has antioxidants that keep radicals in check and protect the body against the
harmful effects of radicals Antioxidants are vitamins C and E We are also exposed to radicals from
cigarette smoke sunbathing pollution and food contaminated with herbicides
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
H
C C
H
H
Alkenes and cycloalkenes are unsaturated hydrocarbons Alkenes have at least one C=C double
bond Aliphatic alkenes with one double bond have the general formula CnH2n They are more
reactive than alkanes and typically take part in addition reactions They can form EZ isomers
including cis-trans isomers
A π-bond is the reactive part of a double bond formed above and below the plane of bonded atoms
by the sideways overlap of p-orbitals Each carbon atom contributes one electron from a p-orbital to
the electron pair in the π-bond which fixes the carbon atoms in position and prevents any rotation
of the bond In alkenes each carbon uses 3 electrons in 3 σ-bonds and 1 electron in one π-bond
Shape of Alkenes
3 regions of electron density surround each carbon atoms in a double bond Pairs of electrons repel
each other as far apart as possible The electron pairs repel each other to give a trigonal planar
shape (120deg)
Cyclic alkenes can be treated the same as branched or straight chained alkenes ndash the react in the
same way
Alkenes are more reactive than alkanes because of the C=C double bond Bond enthalpies show that
a double bond is stronger than a single bond and a π-bond is weaker than a σ-bond When an alkene
breaks the π-bond breaks and the σ-bond stays intact
H
H
C C
H
H
P-orbitals overlap
σ-bond σ-bond
π-bond
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Ni
150degC
C
H
H C
H
H H
H
H
C C
H
H H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
Alkene Reactions
Typically addition reactions
1 A small molecule is added across the double bond causing the π-bond to break
2 2 reactant molecules react together to form on product
3 An unsaturated alkene reacts and forms a saturated alkane
Hydrogenation of Ethene
This is an example of reduction
Halogenation of Ethene
When bromine is added to an alkene sample the colour changes from orange to
colourless The colour change indicates bromine has reacted with the double bond
This is a test for unsaturation it shows the presence of a C=C double bond
Addition of Hydrogen Halides
Hydration of Ethene
A method of preparing alcohols
+ H2
+ Cl2
+ HBr
+ H2O(g) H3PO4
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
C C
H
H H
C
H
H C
H
H H
+
C
H
H C
H
H H
+ C
H
H C
H
H Br
H
Addition of Hydrogen Bromide (electrophilic addition)
+
Hδ+
Brδ-
Br -
Br -
bull In this reaction HBr is
the electrophile
electron pair acceptor
bull HBr is a polar
molecule but non-
polar molecules can
also react with
alkenes
bull The HBr bond breaks
by heterolytic fission
When bromine is added to an
alkene
bull The electrons in the π-
bond repel those in
the Br-Br bond
inducing a dipole in
Br2
bull This forms a
carbocation and a
bromide ion
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
B
C C
A
E D
n C
H
C
H
Cl Cl n
Polymer - A long molecular chain built up from monomer units
Monomer ndash Small molecule that combines with others to form a polymer
If the monomers are alkenes many monomers can be added together to form a long polymer chain
This process is called addition polymerisation
Addition Polymer ndash Very long molecular chain formed by repeated addition reactions of unsaturated
alkene molecules (monomers)
Monomer Polymer (repeated unit)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
The Use of Alkenes
Margarine
The word used for a substance to substitute butter It is made from fats mixed with skimmed milk
and salt Margarine from veg oil is becoming popular for good health people are refusing animal fats
in their diets Margarine with high mono- or polyunsaturated fats are said to be healthier than
butterother margarines Often made from sunflowerolive oil
Veg oils are liquids containing long hydrocarbon chains with many double bonds and are
polyunsaturated The oil must be hardened so it can be spread without being soaked into bread
The oils are hardened by hydrogenation which adds hydrogen molecules across double bonds in an
addition reaction It alters the individual molecule so that the oil partially solidifies and hardens By
adding hydrogen molecules across different numbers of double bonds hardness can vary and
spreadability of margarine can be controlled Partial hydrogenation of unsaturated fats can
transform cis double bonds into trans double bonds as a by-product trans fats are thought to be bad
for health
Poly(phenylethene) Polystyrene is a cheap plastic used in foam packaging insulation model-making
and food retail Polystyrene is being replaced with biodegradable materials as environmental
pressure increases
Poly(propene)Polypropylene is used in food packaging dishwasher safe containers carpet fibres
synthetic ropes It is resistant to chemical attack so is used in certain lab equipment
Addition polymers are durable and do not break down naturally which makes them very useful but
their disposal poses problems
Processing of Waste Polymers
The best way to protect the environment is to re-use polymers without processing
Separation into Types and Recycling
Before plastic waste can be processedconverted it must be sorted Polymer ID codes are used to do
this Optical scanning techniques can separate PET from HDPE bottles Other technologies can
distinguish PVC from other plastics A small quantity of PVC in PET can render the product unsuitable
for re-use PVC is known to release poisonous dioxins when heated
Reclamation
This involves mechanically chopping polymers into small flakes then washing them to remove
impurities The flakes are sent to manufacturing companies where new materials are made by
melting the pellets and remoulding them
PET bottles are converted into carpets clothing and new bottles
HDPE is re-used to make plastic boxes water butts and bins
LDPE waste is made into plastic refuse sacks
Polymers as a Fuel Source
Burning polymers produces heat energy which can be harnessed to generate electricity Agricultural
plastics are being turned into briquettes and are being burned for heat
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
H
C C
H
H
Alkenes and cycloalkenes are unsaturated hydrocarbons Alkenes have at least one C=C double
bond Aliphatic alkenes with one double bond have the general formula CnH2n They are more
reactive than alkanes and typically take part in addition reactions They can form EZ isomers
including cis-trans isomers
A π-bond is the reactive part of a double bond formed above and below the plane of bonded atoms
by the sideways overlap of p-orbitals Each carbon atom contributes one electron from a p-orbital to
the electron pair in the π-bond which fixes the carbon atoms in position and prevents any rotation
of the bond In alkenes each carbon uses 3 electrons in 3 σ-bonds and 1 electron in one π-bond
Shape of Alkenes
3 regions of electron density surround each carbon atoms in a double bond Pairs of electrons repel
each other as far apart as possible The electron pairs repel each other to give a trigonal planar
shape (120deg)
Cyclic alkenes can be treated the same as branched or straight chained alkenes ndash the react in the
same way
Alkenes are more reactive than alkanes because of the C=C double bond Bond enthalpies show that
a double bond is stronger than a single bond and a π-bond is weaker than a σ-bond When an alkene
breaks the π-bond breaks and the σ-bond stays intact
H
H
C C
H
H
P-orbitals overlap
σ-bond σ-bond
π-bond
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Ni
150degC
C
H
H C
H
H H
H
H
C C
H
H H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
Alkene Reactions
Typically addition reactions
1 A small molecule is added across the double bond causing the π-bond to break
2 2 reactant molecules react together to form on product
3 An unsaturated alkene reacts and forms a saturated alkane
Hydrogenation of Ethene
This is an example of reduction
Halogenation of Ethene
When bromine is added to an alkene sample the colour changes from orange to
colourless The colour change indicates bromine has reacted with the double bond
This is a test for unsaturation it shows the presence of a C=C double bond
Addition of Hydrogen Halides
Hydration of Ethene
A method of preparing alcohols
+ H2
+ Cl2
+ HBr
+ H2O(g) H3PO4
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
C C
H
H H
C
H
H C
H
H H
+
C
H
H C
H
H H
+ C
H
H C
H
H Br
H
Addition of Hydrogen Bromide (electrophilic addition)
+
Hδ+
Brδ-
Br -
Br -
bull In this reaction HBr is
the electrophile
electron pair acceptor
bull HBr is a polar
molecule but non-
polar molecules can
also react with
alkenes
bull The HBr bond breaks
by heterolytic fission
When bromine is added to an
alkene
bull The electrons in the π-
bond repel those in
the Br-Br bond
inducing a dipole in
Br2
bull This forms a
carbocation and a
bromide ion
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
B
C C
A
E D
n C
H
C
H
Cl Cl n
Polymer - A long molecular chain built up from monomer units
Monomer ndash Small molecule that combines with others to form a polymer
If the monomers are alkenes many monomers can be added together to form a long polymer chain
This process is called addition polymerisation
Addition Polymer ndash Very long molecular chain formed by repeated addition reactions of unsaturated
alkene molecules (monomers)
Monomer Polymer (repeated unit)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
The Use of Alkenes
Margarine
The word used for a substance to substitute butter It is made from fats mixed with skimmed milk
and salt Margarine from veg oil is becoming popular for good health people are refusing animal fats
in their diets Margarine with high mono- or polyunsaturated fats are said to be healthier than
butterother margarines Often made from sunflowerolive oil
Veg oils are liquids containing long hydrocarbon chains with many double bonds and are
polyunsaturated The oil must be hardened so it can be spread without being soaked into bread
The oils are hardened by hydrogenation which adds hydrogen molecules across double bonds in an
addition reaction It alters the individual molecule so that the oil partially solidifies and hardens By
adding hydrogen molecules across different numbers of double bonds hardness can vary and
spreadability of margarine can be controlled Partial hydrogenation of unsaturated fats can
transform cis double bonds into trans double bonds as a by-product trans fats are thought to be bad
for health
Poly(phenylethene) Polystyrene is a cheap plastic used in foam packaging insulation model-making
and food retail Polystyrene is being replaced with biodegradable materials as environmental
pressure increases
Poly(propene)Polypropylene is used in food packaging dishwasher safe containers carpet fibres
synthetic ropes It is resistant to chemical attack so is used in certain lab equipment
Addition polymers are durable and do not break down naturally which makes them very useful but
their disposal poses problems
Processing of Waste Polymers
The best way to protect the environment is to re-use polymers without processing
Separation into Types and Recycling
Before plastic waste can be processedconverted it must be sorted Polymer ID codes are used to do
this Optical scanning techniques can separate PET from HDPE bottles Other technologies can
distinguish PVC from other plastics A small quantity of PVC in PET can render the product unsuitable
for re-use PVC is known to release poisonous dioxins when heated
Reclamation
This involves mechanically chopping polymers into small flakes then washing them to remove
impurities The flakes are sent to manufacturing companies where new materials are made by
melting the pellets and remoulding them
PET bottles are converted into carpets clothing and new bottles
HDPE is re-used to make plastic boxes water butts and bins
LDPE waste is made into plastic refuse sacks
Polymers as a Fuel Source
Burning polymers produces heat energy which can be harnessed to generate electricity Agricultural
plastics are being turned into briquettes and are being burned for heat
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Ni
150degC
C
H
H C
H
H H
H
H
C C
H
H H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
H
C C
H
H H
C
H
H C
H
Cl Cl
H
Alkene Reactions
Typically addition reactions
1 A small molecule is added across the double bond causing the π-bond to break
2 2 reactant molecules react together to form on product
3 An unsaturated alkene reacts and forms a saturated alkane
Hydrogenation of Ethene
This is an example of reduction
Halogenation of Ethene
When bromine is added to an alkene sample the colour changes from orange to
colourless The colour change indicates bromine has reacted with the double bond
This is a test for unsaturation it shows the presence of a C=C double bond
Addition of Hydrogen Halides
Hydration of Ethene
A method of preparing alcohols
+ H2
+ Cl2
+ HBr
+ H2O(g) H3PO4
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
C C
H
H H
C
H
H C
H
H H
+
C
H
H C
H
H H
+ C
H
H C
H
H Br
H
Addition of Hydrogen Bromide (electrophilic addition)
+
Hδ+
Brδ-
Br -
Br -
bull In this reaction HBr is
the electrophile
electron pair acceptor
bull HBr is a polar
molecule but non-
polar molecules can
also react with
alkenes
bull The HBr bond breaks
by heterolytic fission
When bromine is added to an
alkene
bull The electrons in the π-
bond repel those in
the Br-Br bond
inducing a dipole in
Br2
bull This forms a
carbocation and a
bromide ion
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
B
C C
A
E D
n C
H
C
H
Cl Cl n
Polymer - A long molecular chain built up from monomer units
Monomer ndash Small molecule that combines with others to form a polymer
If the monomers are alkenes many monomers can be added together to form a long polymer chain
This process is called addition polymerisation
Addition Polymer ndash Very long molecular chain formed by repeated addition reactions of unsaturated
alkene molecules (monomers)
Monomer Polymer (repeated unit)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
The Use of Alkenes
Margarine
The word used for a substance to substitute butter It is made from fats mixed with skimmed milk
and salt Margarine from veg oil is becoming popular for good health people are refusing animal fats
in their diets Margarine with high mono- or polyunsaturated fats are said to be healthier than
butterother margarines Often made from sunflowerolive oil
Veg oils are liquids containing long hydrocarbon chains with many double bonds and are
polyunsaturated The oil must be hardened so it can be spread without being soaked into bread
The oils are hardened by hydrogenation which adds hydrogen molecules across double bonds in an
addition reaction It alters the individual molecule so that the oil partially solidifies and hardens By
adding hydrogen molecules across different numbers of double bonds hardness can vary and
spreadability of margarine can be controlled Partial hydrogenation of unsaturated fats can
transform cis double bonds into trans double bonds as a by-product trans fats are thought to be bad
for health
Poly(phenylethene) Polystyrene is a cheap plastic used in foam packaging insulation model-making
and food retail Polystyrene is being replaced with biodegradable materials as environmental
pressure increases
Poly(propene)Polypropylene is used in food packaging dishwasher safe containers carpet fibres
synthetic ropes It is resistant to chemical attack so is used in certain lab equipment
Addition polymers are durable and do not break down naturally which makes them very useful but
their disposal poses problems
Processing of Waste Polymers
The best way to protect the environment is to re-use polymers without processing
Separation into Types and Recycling
Before plastic waste can be processedconverted it must be sorted Polymer ID codes are used to do
this Optical scanning techniques can separate PET from HDPE bottles Other technologies can
distinguish PVC from other plastics A small quantity of PVC in PET can render the product unsuitable
for re-use PVC is known to release poisonous dioxins when heated
Reclamation
This involves mechanically chopping polymers into small flakes then washing them to remove
impurities The flakes are sent to manufacturing companies where new materials are made by
melting the pellets and remoulding them
PET bottles are converted into carpets clothing and new bottles
HDPE is re-used to make plastic boxes water butts and bins
LDPE waste is made into plastic refuse sacks
Polymers as a Fuel Source
Burning polymers produces heat energy which can be harnessed to generate electricity Agricultural
plastics are being turned into briquettes and are being burned for heat
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
H
C C
H
H H
C
H
H C
H
H H
+
C
H
H C
H
H H
+ C
H
H C
H
H Br
H
Addition of Hydrogen Bromide (electrophilic addition)
+
Hδ+
Brδ-
Br -
Br -
bull In this reaction HBr is
the electrophile
electron pair acceptor
bull HBr is a polar
molecule but non-
polar molecules can
also react with
alkenes
bull The HBr bond breaks
by heterolytic fission
When bromine is added to an
alkene
bull The electrons in the π-
bond repel those in
the Br-Br bond
inducing a dipole in
Br2
bull This forms a
carbocation and a
bromide ion
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
B
C C
A
E D
n C
H
C
H
Cl Cl n
Polymer - A long molecular chain built up from monomer units
Monomer ndash Small molecule that combines with others to form a polymer
If the monomers are alkenes many monomers can be added together to form a long polymer chain
This process is called addition polymerisation
Addition Polymer ndash Very long molecular chain formed by repeated addition reactions of unsaturated
alkene molecules (monomers)
Monomer Polymer (repeated unit)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
The Use of Alkenes
Margarine
The word used for a substance to substitute butter It is made from fats mixed with skimmed milk
and salt Margarine from veg oil is becoming popular for good health people are refusing animal fats
in their diets Margarine with high mono- or polyunsaturated fats are said to be healthier than
butterother margarines Often made from sunflowerolive oil
Veg oils are liquids containing long hydrocarbon chains with many double bonds and are
polyunsaturated The oil must be hardened so it can be spread without being soaked into bread
The oils are hardened by hydrogenation which adds hydrogen molecules across double bonds in an
addition reaction It alters the individual molecule so that the oil partially solidifies and hardens By
adding hydrogen molecules across different numbers of double bonds hardness can vary and
spreadability of margarine can be controlled Partial hydrogenation of unsaturated fats can
transform cis double bonds into trans double bonds as a by-product trans fats are thought to be bad
for health
Poly(phenylethene) Polystyrene is a cheap plastic used in foam packaging insulation model-making
and food retail Polystyrene is being replaced with biodegradable materials as environmental
pressure increases
Poly(propene)Polypropylene is used in food packaging dishwasher safe containers carpet fibres
synthetic ropes It is resistant to chemical attack so is used in certain lab equipment
Addition polymers are durable and do not break down naturally which makes them very useful but
their disposal poses problems
Processing of Waste Polymers
The best way to protect the environment is to re-use polymers without processing
Separation into Types and Recycling
Before plastic waste can be processedconverted it must be sorted Polymer ID codes are used to do
this Optical scanning techniques can separate PET from HDPE bottles Other technologies can
distinguish PVC from other plastics A small quantity of PVC in PET can render the product unsuitable
for re-use PVC is known to release poisonous dioxins when heated
Reclamation
This involves mechanically chopping polymers into small flakes then washing them to remove
impurities The flakes are sent to manufacturing companies where new materials are made by
melting the pellets and remoulding them
PET bottles are converted into carpets clothing and new bottles
HDPE is re-used to make plastic boxes water butts and bins
LDPE waste is made into plastic refuse sacks
Polymers as a Fuel Source
Burning polymers produces heat energy which can be harnessed to generate electricity Agricultural
plastics are being turned into briquettes and are being burned for heat
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
B
C C
A
E D
n C
H
C
H
Cl Cl n
Polymer - A long molecular chain built up from monomer units
Monomer ndash Small molecule that combines with others to form a polymer
If the monomers are alkenes many monomers can be added together to form a long polymer chain
This process is called addition polymerisation
Addition Polymer ndash Very long molecular chain formed by repeated addition reactions of unsaturated
alkene molecules (monomers)
Monomer Polymer (repeated unit)
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
The Use of Alkenes
Margarine
The word used for a substance to substitute butter It is made from fats mixed with skimmed milk
and salt Margarine from veg oil is becoming popular for good health people are refusing animal fats
in their diets Margarine with high mono- or polyunsaturated fats are said to be healthier than
butterother margarines Often made from sunflowerolive oil
Veg oils are liquids containing long hydrocarbon chains with many double bonds and are
polyunsaturated The oil must be hardened so it can be spread without being soaked into bread
The oils are hardened by hydrogenation which adds hydrogen molecules across double bonds in an
addition reaction It alters the individual molecule so that the oil partially solidifies and hardens By
adding hydrogen molecules across different numbers of double bonds hardness can vary and
spreadability of margarine can be controlled Partial hydrogenation of unsaturated fats can
transform cis double bonds into trans double bonds as a by-product trans fats are thought to be bad
for health
Poly(phenylethene) Polystyrene is a cheap plastic used in foam packaging insulation model-making
and food retail Polystyrene is being replaced with biodegradable materials as environmental
pressure increases
Poly(propene)Polypropylene is used in food packaging dishwasher safe containers carpet fibres
synthetic ropes It is resistant to chemical attack so is used in certain lab equipment
Addition polymers are durable and do not break down naturally which makes them very useful but
their disposal poses problems
Processing of Waste Polymers
The best way to protect the environment is to re-use polymers without processing
Separation into Types and Recycling
Before plastic waste can be processedconverted it must be sorted Polymer ID codes are used to do
this Optical scanning techniques can separate PET from HDPE bottles Other technologies can
distinguish PVC from other plastics A small quantity of PVC in PET can render the product unsuitable
for re-use PVC is known to release poisonous dioxins when heated
Reclamation
This involves mechanically chopping polymers into small flakes then washing them to remove
impurities The flakes are sent to manufacturing companies where new materials are made by
melting the pellets and remoulding them
PET bottles are converted into carpets clothing and new bottles
HDPE is re-used to make plastic boxes water butts and bins
LDPE waste is made into plastic refuse sacks
Polymers as a Fuel Source
Burning polymers produces heat energy which can be harnessed to generate electricity Agricultural
plastics are being turned into briquettes and are being burned for heat
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
The Use of Alkenes
Margarine
The word used for a substance to substitute butter It is made from fats mixed with skimmed milk
and salt Margarine from veg oil is becoming popular for good health people are refusing animal fats
in their diets Margarine with high mono- or polyunsaturated fats are said to be healthier than
butterother margarines Often made from sunflowerolive oil
Veg oils are liquids containing long hydrocarbon chains with many double bonds and are
polyunsaturated The oil must be hardened so it can be spread without being soaked into bread
The oils are hardened by hydrogenation which adds hydrogen molecules across double bonds in an
addition reaction It alters the individual molecule so that the oil partially solidifies and hardens By
adding hydrogen molecules across different numbers of double bonds hardness can vary and
spreadability of margarine can be controlled Partial hydrogenation of unsaturated fats can
transform cis double bonds into trans double bonds as a by-product trans fats are thought to be bad
for health
Poly(phenylethene) Polystyrene is a cheap plastic used in foam packaging insulation model-making
and food retail Polystyrene is being replaced with biodegradable materials as environmental
pressure increases
Poly(propene)Polypropylene is used in food packaging dishwasher safe containers carpet fibres
synthetic ropes It is resistant to chemical attack so is used in certain lab equipment
Addition polymers are durable and do not break down naturally which makes them very useful but
their disposal poses problems
Processing of Waste Polymers
The best way to protect the environment is to re-use polymers without processing
Separation into Types and Recycling
Before plastic waste can be processedconverted it must be sorted Polymer ID codes are used to do
this Optical scanning techniques can separate PET from HDPE bottles Other technologies can
distinguish PVC from other plastics A small quantity of PVC in PET can render the product unsuitable
for re-use PVC is known to release poisonous dioxins when heated
Reclamation
This involves mechanically chopping polymers into small flakes then washing them to remove
impurities The flakes are sent to manufacturing companies where new materials are made by
melting the pellets and remoulding them
PET bottles are converted into carpets clothing and new bottles
HDPE is re-used to make plastic boxes water butts and bins
LDPE waste is made into plastic refuse sacks
Polymers as a Fuel Source
Burning polymers produces heat energy which can be harnessed to generate electricity Agricultural
plastics are being turned into briquettes and are being burned for heat
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days
F322 Chains Energy and Resources
Module 1 Basic Concepts amp Hydrocarbons
Feedstock Recycling
Processes are being developed to convert polymers into synthesis gas a mixture of H2 and CO which
can be used as chemical feedstock for conversion into useful products or as fuel at oil refineries
Scientists are working to increase the efficiency and cost-effectiveness of feedstock recycling
Recycling PVC - poly(vinyl chloride)
This is problematic because of its high chlorine content Recycling PVC is uneconomical because the
cost of recycling makes the end product more expensive than that made from crude oil
Incineration has been used to prevent PVC going into landfill sites Combustion of PVC releases toxic
fumes into the environment and may cause corrosion in the plant itself HCl fumes are also detected
when PVC is heated to high temps as part of the recycling process Incinerators are equipped with
pollution control apparatus to minimise such emissions New technology ndash PVC is separated from
other scrap by dissolving in solvents High-quality PVC is recovered by precipitation from the solvent
The solvent is recovered and used again This recycles the PVC coatings of wiring and other PVC
waste
Biodegradable and Compostable Polymers
Bioplastics are derived from starch maize cellulose and lactic acid and are biodegradable or
compostable Bioplastics are kinder to the environment and degrade naturally to carbon dioxide and
water
bull Bioplastic breaks down due to bacterial activity
bull Bioplastics have strict criteria must break down by a biological process to CO2 H2O
inorganic compounds and biomass Compostable plastics break down in a similar time frame
as natural compostable materials
bull Bags and cutlery made from cornstarch could replace oil-derived polythene in the future
Supermarket bags can also be made from plant starch and can be used as bin liners to collect
food waste The bag and waste can be composted together
bull Compostable disposable tableware made from sugar cane fibre are replacing polystyrene
products
bull Poly(lactic acid) is used for cold drink cups that biodegrade in 180 days