Chemistry 2 Molecular Quantities

J Young

A chemical change: any change in which a new substance is formed.

Evidence of a Chemical Change:

Release of energy as heat

Release of energy as light

Change in colour

Formation of a gas

Change in odour…

1. Neutralization: Acid(H) + Base(OH) salt + H(OH)

2. Combustion: AB + oxygen CO2 + H2O

3. Synthesis: A + B AB

4. Decomposition: AB A + B

5. Single displacement: A + BC AC + B

6. Double displacement: AB + CD AD + CB

–A + B AB where A and B represent elements

– The elements may form ionic compounds, like…

– Sodium metal and chlorine gas combine to form sodium chloride.

– 2Na + Cl2 2NaCl

Sodium added to chlorine gas

Synthesis reactions are also known as FORMATION reactions.Two or more reactants (usually elements) join to form a compound.

• Decomposition reactions are the opposite of synthesis reactions.– A compounds breaks down into two or more

products (often elements).–AB A + B

where A and B represent elements

1. Ionic compounds may decompose to produce elements, like the following:

• Table salt, sodium chloride, can be broken down into sodium metal and chlorine gas by melting salt at 800ºC and running electricity through it.

• 2NaCl 2Na + Cl2

(c) McGraw Hill Ryerson 2007

See page 260

Types: Decomposition

Example: NaCl

General: AB A + B

Cl Na Cl + Na

Types: Decomposition

Example 2HgO

O Hg

O Hg

Hg

O O Hg

+

General: AB A + B

2. Covalent compounds may decompose into elements, like the following:

• By running electricity through water, the water molecules decompose into hydrogen and oxygen gases.

• 2H2O 2H2 + O2

DECOMPOSITION REACTION:

http://www.youtube.com/watch?v=NddwtXEA_Ak

• Single replacement reactions replace one element from a compound with another element.– A compound and an element react, and the

element switches places with part of the original compound.• A + BC B + AC where A is a metal, or

• A + BC C + BA where A is a non-metal

Types: Single displacement

Example: Zn + CuCl2

ZnClCl Cu +

General: AB + C AC + B

ClCl Zn Cu+

1. When A is a metal:• Aluminum foil in a solution of copper(II)

chloride produces solid copper and aluminum chloride.

• 2Al + 3CuCl2 3Cu + 2AlCl3

2. When A is a non-metal:• When fluorine is bubbled through a sodium

iodide solution, iodine and sodium fluoride are produced.

• Fl2 + 2NaI I2 + 2NaFSINGLE REPLACEMENT:

http://www.youtube.com/watch?v=hKtynbVtMKc

(c) McGraw Hill Ryerson 2007

• Double replacement reactions swap elements between 2 compounds that react together to form two new compounds.– Two compounds react, with elements switching

places between the original compounds.

AB + CD AD + CB

See page 262

(c) McGraw Hill Ryerson 2007

See page 262

Types: Double displacement

Example: MgO + CaS

General: AB + CD AD + CB

SOMg Ca

+O S

Mg Ca+

(c) McGraw Hill Ryerson 2007

– When potassium chromate and silver nitrate react, they form a red precipitate, silver chromate, in a solution of potassium nitrate.

– K2CrO4 + 2AgNO3 Ag2CrO4 + 2KNO3 silver chromate

Two solutions react to form a precipitate (solid) and another solution.

Ionic solution + ionic solution ionic solution + ionic solid.

AB + CD AD + CB

DOUBLE REPLACEMENT:http://www.youtube.com/watch?v=opY3FLrPTa4

(c) McGraw Hill Ryerson 2007

• Neutralization reactions occur when an acid (most compounds starting with H) and a base (most compounds ending in OH) react to form a salt and water.

• Neutralization reactions are a type of double replacement.

• Acid + base salt + water

HHX + MOHOH MX + H2O where X and M are elements

See page 263

(c) McGraw Hill Ryerson 2007

1. Sulfuric acid is used to neutralize calcium hydroxide:• H2SO4 + Ca(OH) 2 CaSO4 + 2H2O

2. Phosphoric acid helps to neutralize the compounds that cause rust, such as iron(II) hydroxide.• H3PO4 + 3Fe(OH)2 Fe3(PO4)2 + 6H2O

See page 263

NEUTRALIZATION:http://www.youtube.com/watch?v=_P5hGzA6Vb0

(c) McGraw Hill Ryerson 2007

• Combustion reactions occur when a compound or element react with oxygen to release energy and produce an oxide.– Also sometimes referred to as hydrocarbon

combustion.

CXHY + O2 CO2 + H2O where X and Y represent integers

See page 264

METHANOL + oxygen: http://www.youtube.com/watch?v=98JuJ-G1qXY&feature=related

(c) McGraw Hill Ryerson 2007

1. Natural gas (methane) is burned in furnaces to heat homes.

»CH4 + O2 CO2 + 2H2O + energy

2. An acetylene torch is used to weld metals together.

»2C2H2 + 5O2 4CO2 + 2H2O + energy

3. Carbohydrates like glucose combine with oxygen in our body to release energy.

»C6H12O6 + 6O2 6CO2 + 6H2O + energy See page 264

Acetylene torch

(c) McGraw Hill Ryerson 2007

See page 265Take the Section 6.1 Quiz

MOVIE TO REVIEW: http://www.bcscience.com/bc10/pgs/videos_013_chemical_reactions.html

Combustion Reactions

• Rapid oxidation of fuel source

• All process reboilers and heaters

• Auto ignition of pyrophoric materials like Iron Sulfide

Neutralization Reactions

• Boiler feed water treatment

• Waste water treatment facility

• Chloride traps – reformer

• Caustic Scrubbers in many units.

Exothermic and Endothermic

• Exothermic reactions.– Give off energy,

mainly heat.– Reaction will sustain

itself, continuing until all reactants are gone.

– Accelerates. More heat, more reaction. More reaction, more heat.

• Endothermic reactions– Requires energy

input, mainly heat– Reaction will

discontinue with loss of energy source

Examples of Exothermic and

Endothermic• Hydrotreating

reactions are exothermic– DHDS Unit– Hydrocracker– NHDS Unit– Isom

• Reforming reactions are endothermic

Solutions and Concentrations

• Characteristics of solutions

• Percent-by-weight solutions

• pH measurement• Homogeneous

solutions

Homogeneous Solutions

• Crude oil.– Evenly mixed solution of hydrocarbons

from methane to asphalt.– Each type of molecule has its own

properties.• Boiling point.• Vapor pressure.• Melting point.

– Refineries are based on the physical properties of hydrocarbons.

Oxidation and reduction in terms of oxygen transferDefinitionsOxidation is gain of oxygen.Oxidizing agents give oxygen to another substance or remove hydrogen from it.

Reduction is loss of oxygen.Reducing agents remove oxygen from another substance or give hydrogen to it.Oxidation and reduction in terms of electron transferThis is easily the most important use of the terms oxidation and reduction at A' level.DefinitionsOxidation is loss of electrons.Reduction is gain of electrons.

Source: http://www.chemguide.co.uk/inorganic/redox/definitions.html

Reduction Oxidation (Redox) 1

Oxidation and reduction in terms of hydrogen transferThese are old definitions which aren't used very much nowadays. The most likely place you will come across them is in organic chemistry.DefinitionsOxidation is loss of hydrogen.Reduction is gain of hydrogen.Notice that these are exactly the opposite of the oxygen definitions.For example, ethanol can be oxidized to ethanal:

Reduction Oxidation (Redox) 2

Oxidation and reduction in terms of electron transferThis is easily the most important use of the terms oxidation and reduction at A' level.DefinitionsOxidation is loss of electrons.Reduction is gain of electrons.

The equation shows a simple redox reaction which can obviously be described in terms of oxygen transfer.

CuO + Mg Cu + MgO

Reduction Oxidation (Redox) 3

THE END