Chemistry ERT (Fuels)

Produce a briefing report to the federal Government where you will analyse data about a number of compounds which have been considered or used in the past as possible suitable fuels either for cooking or for vehicle transportation.

As part of this, you will then investigate various replacements for petrol and look at the pros and cons of each replacement with regard to the energy density, enthalpies of combustion, bond dissociation enthalpies and the production and ease of use.

In the final part, you are asked to produce a briefing document which advises the Federal Government which link the suitability of fuels with their physical and chemical properties and their feasibility for replacing petrol for vehicle transportation.

a.) What properties do you think a good fuel should have? Link these fuel properties to chemical and physical structure.

Volatility Volatility is a measure of how likely a liquid is to evaporate. It is very important that the fuel have a moderate volatility so that the substance may change from liquid to gas as required by the system. Highly volatile substances evaporate readily in air, making the fuel difficult to store. Ideally, a fuel should be somewhat volatile, so that it can combine readily with the air when sprayed into the intake manifold (a set of tubes which lead to the internal combustion engine) to produce combustible vapour; however, the fuel should not be so volatile that it exists almost completely in a gaseous state.

Economic Viability It is important that the fuel be economically viable and available to a wide range of people. It is also important the fuel be easy to produce in large quantities.

Octane Rating Internal combustion engines can often exhibit undesirable behaviour where the fuel ignites at an unsuitable time, often causing severe damage to the system. This action is referred to as ‘knocking’ and is more prevalent within some fuels than others. The octane rating is a measure of how likely a fuel is to self-ignite. The fuel’s propensity to cause knocking is compared to a mixture of heptane and iso-octane (2, 2, 4-trimethyloctane). (Brennan, J 2012) A fuel which possesses the same anti-knocking capability as a mixture of 50% heptane and 50% iso-octane would have an octane rating of 50. Therefore, good fuels should have high octane ratings.

Activation Energy Activation energy is defined as the amount of energy required to initiate a reaction. If the activation barrier is too high, then a great deal of energy must be supplied in order to start the reaction. On the other hand, if the activation energy is too low, then the reaction becomes unstable and potentially hazardous to human health and safety. Therefore, it is important that the fuel have a moderate activation energy.

Ash Content It is very important that a fuel be free from ash content. The formation of ash during combustion is due to the presence of inorganic matter in the fuel. High ash content is very undesirable

and the disposal of the ash poses problems. Energy Density Energy density refers to the amount of energy stored within a

fuel per unit volume. A good fuel should have a high energy density with regards to both variable density (the density is variable due to the constant changes in temperature and pressure) and specific energy (energy mass per unit). This allows for the energy to be transported more efficiently in the form of a fuel. In other words, energy density is a measure of how compactly hydrogen atoms are packed in a fuel.

Enthalpy Change of Combustion

The standard enthalpy change of combustion is defined as the amount of energy released when one mole of an element or compound reacts completely with oxygen under standard conditions. In a chemical reaction, bonds between atoms are broken and formed. Breaking bonds requires energy, whereas making bonds releases energy. Different types of bonds require different amounts of energy to be broken, and release different amounts of energy when they are formed (Davies, S 2010). These amounts are called bond enthalpies, can be totalled to give the overall enthalpy of combustion. By definition, combustion reactions are exothermic because the energy released during bond formation is greater than the energy absorbed through breaking bonds, and thus, it results in a negative enthalpy change. Therefore, a good fuel should have a very high enthalpy change of combustion, meaning that it releases a great deal of energy when burned.

Corrosion It is very important that the fuel be as non-corrosive as possible, meaning that it would not deteriorate or destruct the system during chemical reactions.

Viscosity Viscosity refers to the consistency of a substance and is also a measure of its resistance to internal flow. Ideally, a fuel should retain a moderate viscosity, so that it possesses some resistance to internal flow, but it is not so viscous that it becomes difficult to handle.

Melting/Boiling Points It is important that the fuel have a low melting point, as it must be a liquid in order to be used. It should also have a relatively low boiling point, so that it is somewhat volatile.

Flash Point The flash point of a chemical is fuel is defined as the lowest temperature where enough fluid can evaporate to produce a combustible concentration of gas. (Engineering ToolBox, 2012) Ideally, a fuel should have a high flash point, as fuels with low flash points are very flammable and hazardous.

Specific Heat Specific heat is defined as the amount of energy (kcals) required to raise the temperature of 1kg of oil by 1℃. It determines the amount of electrical energy or steam required to heat the fuel to the desired temperature. A good fuel should have a low specific heat, meaning that a minimal amount of kcals are required to heat the fuel to a certain temperature. As a general rule, light fuels have a low specific heat, and heavier fuels have a high specific heat.

Moderate Ignition Point Ignition temperature is defined as the minimum temperature to which the fuel must be heated in order to initiate the

combustion. If the ignition temperature is too low, the risk of fire hazards during handling, storage, transportation and application is greatly increased. On the other hand, if the ignition temperature is too high, then igniting the fuel becomes difficult. Moderate ignition temperature is perhaps the most desired property of a fuel.

Ease of Transport/Storage

Fuels should be easy to store and transport effectively. They should not occupy too much space or demand complex and expensive arrangements for their storage or transportation. In addition to this, there must be minimal risks of fire hazards.

Harmless Combustion Products

A good fuel must not produce harmful combustion products such as CO, SO2, NO, smoke, etc. and must therefore, burn with a clean flame. The formation of such by-products poses a severe risk to human health and safety and can also be detrimental to the environment.

Low Moisture Content The presence of a high percentage of water or moisture in the fuel is highly undesirable as it decreases the efficiency of the fuel. It also raises the ignition temperature, making the fuel difficult to burn. Furthermore, it lowers the amount of energy released from the combustion as some of the heat produced is used up in order to vaporise the moisture. Therefore, the presence of water in a fuel should be negligible.

Structural Attributes

There are several important structural attributes which must be considered prior to selecting fuels for use. In several cases, the size of a molecule may have an effect upon the physical and chemical properties of the molecule. Consider the structure of basic hydrocarbons: as the carbon chain length increases, as does the theoretical enthalpy of combustion. Ideally, a hydrocarbon fuel should contain short alkane chains as smaller molecules generally have higher octane ratings than longer alkane chains. However, they must also be long enough to release a significant amount of energy upon combustion.

b.) Conduct your own secondary research into some other important sources of data relating to the fuels listed in the table below, and include this in your analysis. Analyse the data in the table concerning a range of fuels, identify relationships between patterns, trends, errors and anomalies. Show the findings in a suitable way.

Some compounds derived from alkanes are commonly used as fuels. Some data is included in the table below.

Fuel Formula Theoretical Enthalpy of Combustion KJ mol-1

Energy Density KJ kg-1

Decane C10H22 - 6778 - 48 000Octane C8H18 - 5470 - 47 700Hexane C6H14 - 4163 - 48 400

Methane CH4 - 890 - 55 600Methanol CH3OH - 726 - 22 700Ethanol C2H5OH - 1371 - 30 000Hydrogen H2 - 286 - 143 000

The table below outlines some of the key properties of these compounds aside from those listed in the table above. Some of these properties include molecular structure, carbon chain length, molecular weight, flash point, ignition temperature as well as melting and boiling points. Each of these properties is important to consider when identifying relationships between patterns, trends and anomalies in each of the different compounds.

Fuel Molecular Structure Flash Point Ignition Temperature

Melting Point/ Boiling Point

No./Molecular Weight

Decane (C10H22)

46℃ 210℃ Melting Point = -29℃

Boiling Point = 174℃

No. of carbon atoms = 10 carbon atoms

Molecular Weight = 142.48g/mol

Octane (C8H18)





Hexane (C6H14)

-22℃ 225℃ Melting Point = -96℃




Methane (CH4)

-188℃ 540℃ Melting Point = -182℃

Boiling Point = -164℃

No. of carbon atoms = 1 carbon atom


Methanol (CH3OH)


Boiling Point = 64.5

No. of carbon atoms = 1 carbon atom


Ethanol (C2H5OH)





Hydrogen (H2)

-253℃ 520℃ Melting Point = -259℃

Boiling Point = -253℃



Theoretical Enthalpy of Combustion

As can be noted from the data collated in the table above, there is a strong relationship between the size of the molecule and the theoretical enthalpy of combustion. As a general rule – the larger the molecule, the higher the enthalpy of combustion. For example, the compound with the longest carbon chain and consequently, the largest molecular size is decane – an alkane comprising of 10 carbon atoms and 22 hydrogen atoms joined together with single bonds. As well as having the largest molecular size, decane also has the greatest enthalpy of combustion of 6778 KJ mol-1. Furthermore, the compound with the smallest molecular size, hydrogen, which contains only two hydrogen atoms, has the lowest theoretical enthalpy of combustion of 286 KJ mol-1. This is due to the significantly higher number of bonds in decane as compared to hydrogen; therefore, more energy must be supplied in order to break the bonds, and subsequently, more energy is released upon combustion. This is called an exothermic reaction. This trend can be seen in the graph below (Figure 1). Note the linear relationship between the number of carbon atoms and the theoretical enthalpy of combustion.

0 2 4 6 8 10 120

1000

2000

3000

4000

5000

6000

7000

8000

Number of Carbon Atoms/Theoretical Enthalpy of Combustion

Compounds

Number of Carbon Atoms

Theo

retic

al E

ntha

lpy

of C

ombu

stion

(KJ m

ol-1

)

Figure 1: This graph represents the relationship between the molecular size and the theoretical enthalpy of combustion of different compounds.

Ignition Temperature

Another relationship which can be identified from the data listed in the tables above is that between the ignition temperature of the compound and the number of carbon atoms present within the substance. As a general trend, the greater the number of carbons, the lower the ignition temperature. For example, methane, which is the smallest hydrocarbon molecule, has an ignition temperature of approximately 540°C, and the largest molecule, decane, has an ignition temperature of approximately 210°C. This general trend is applicable to most of the substances listed in the tables. However, it must be noted that although hydrogen possesses a very high ignition temperature, it also does not contain any carbon atoms and therefore, the trend does not extend to it. This general pattern is represented in Figure 2 (below).

0 2 4 6 8 10 120

100

200

300

400

500

600

Ignition Temperature/Number of Carbon Atoms

Compounds


Igni

tion

Tem

pera

ture

(°C)

Figure 2: This graph represents the relationship between ignition temperature and molecular size.

Energy Density of Hydrocarbons and Alcohols

It can be discerned from the data presented in the tables, that the alcohols possess much lower energy density values than the hydrocarbons. Energy density is defined as the amount of energy stored within a given volume of a particular substance. As a general rule, the energy density of a particular substance can be determined by dividing the energy released during combustion by the molecular mass. For this reason, alcohols, which are already in a partially oxidised state, and therefore do not combust completely, release significantly less energy upon combustion and therefore, they have a lower energy density. For this reason, as a general rule, the larger the alcohol molecule, the lower the energy density. For example, ethanol has a molecular weight of approximately 46.0g/mol and contains two carbon atoms. On the other hand, methanol has a molecular weight of approximately 32.04g/mol and contains only one carbon and consequently, has a higher energy density than ethanol. In addition to this, due to the presence of an oxygen atom in the molecule, alcohol fuels tend to weigh more than hydrocarbons containing the same number of carbon atoms. This relationship can be seen in the graph below (Figure 3).

Decane

Octane

Hexan

e

Methan

e

Methan

ol

Ethan

ol

Hydro

gen

0

20000

40000

60000

80000

100000

120000

140000

160000

Relationship Beween Energy Density of Hydrocarbons/Energy Density of Alcohols

Energy Density KJ kg-1

Ener

gy D

ensit

y KJ

kg-

1

Figure 3: This graph represents the relationship between the energy densities of hydrocarbons and alcohols.

Flash Point

Another relationship in the data is that between the flash point and the molecular size. As a general trend, the greater the number of carbon atoms in the compound, the higher the flash point. For example, decane, which is the largest molecule, has a flash point of approximately 46°C and hydrogen, being the smallest molecule has a flash point of approximately -253°C. However, there are some exceptions to this general trend – the two alcohols, methanol and ethanol, both have higher flash points than normal hydrocarbons containing the same number of carbon atoms. This is due to the fact that the two alcohol compounds both contain an oxygen atom, and therefore are more flammable than standard hydrocarbons. This trend is represented in Figure 4 below.

0 2 4 6 8 10 12

-300

-250

-200

-150

-100

-50

0

50

100

Number of Carbon Atoms/Flash Point


Flas

h Po

int (

°C)

Figure 4: This graph represents the relationship between the flash points and molecular sizes of different compounds.

c.) Investigate various replacements for petrol and look at the pros and cons of each replacement with regards to the energy density, enthalpies of combustion, bond dissociation enthalpies and its production and ease of use and its environmental impact.

1. Hydrogen (H2)

Hydrogen is a zero-emission fuel which uses electrochemical cells or combustion in internal engines, to power vehicles. Hydrogen is the first element on the periodic table and consequently, it is the lightest element on earth. Furthermore, it is the most abundant element on earth; however, it is very rarely found in its pure form (H2) because being so light, it rises into the outermost layers of the atmosphere. The heat released when hydrogen reacts with oxygen to produce water and CO2 in a flame of pure hydrogen gas is what is used as he fuel. Therefore, hydrogen is an energy carrier, rather than an energy source. The table below outlines some of the key advantages and disadvantages of hydrogen as a fuel.

Advantages Disadvantages Hydrogen-powered cars only

produce water as a by-product, rather than pollutants or other harmful contaminants, making it very environmentally friendly.

Since hydrogen is the most abundant element on Earth, it would not be exhausted unlike

Hydrogen is a gas, making it extremely difficult to store in a liquid state. Special containers would have to be developed for the sole purpose of storing hydrogen fuel.

Hydrogen is highly corrosive to steel, making storage in vehicles an

other fossil fuels. Approximately 70% of the earth’s surface is covered in water, meaning that hydrogen is readily available on Earth.

Up to 90% of the energy produced by the fuel cell in hydrogen-powered cars can be converted to electrical energy.

Hydrogen burns cleanly. Hydrogen fuel is exponentially

cleaner than all other fuels. Even when combusted in combination with hydrocarbon fuels, there is hardly any environmental impact.

Hydrogen has one of the highest energy density values per mass (143 000 KJ kg-1) and therefore releases a large amount of energy upon combustion, which is very desirable for a fuel as it means that the vehicle will have greater mileage.

There are no carbon-based emissions associated with hydrogen fuel, as the only by-product of combustion is water.

Moderate bond dissociation enthalpy (104 kcals) – this means that a moderate amount of energy must be supplied to break the bond between the two hydrogen atoms to initiate the combustion reaction.

High enthalpy of combustion – releases a large amount of energy when burned

issue. Because hydrogen does not occur

naturally, it requires a great deal of energy to manufacture it by separating hydrogen from a hydrogen-containing compound, which is often very expensive. For example, if hydrogen is to be extracted form water, the water must be purified, passed through a very strong electrical current and the gas must be captured and stored in a sealed, non-conductive container to prevent the risk of explosion.

Ironically, fossil fuels such as oil and coal are often used in the production of hydrogen, either to provide electricity to separate it from water through electrolysis or as the material from which the hydrogen is separated. This use of fossil fuels may defeat the purpose of the benefits of hydrogen as an alternative fuel.

There is currently no existing transportation infrastructure, making transportation an issue.

Low octane rating – prone to ‘knocking’

Hydrogen is highly reactive and reacts with almost everything. It is also highly flammable, with the same self-ignition temperature as methane.

There is currently no existing delivery network.

Handling liquid hydrogen requires extreme safety precautions due to its high volatility and extremely cold temperature (-253℃).

The fuel cells used in automobiles require the element platinum in order for them to function properly; however, platinum is a relatively rare element, and therefore, is quite expensive.

Because hydrogen is a rapidly-dissipating gas and also the lightest element on earth, a great deal of energy is required to compress it

into a liquid form, which is also very expensive.

Leakage from using hydrogen as a fuel source could be very detrimental to the ozone layer, possibly degrading it faster than chlorofluorocarbons.

Not effective for use in temperatures below 30℃

2. Ethanol (C2H5OH)

Ethanol fuel is a liquid hydrocarbon and is often used as a motor fuel, mainly as a biofuel additive for gasoline. Ethanol is a renewable energy source, as it is produced from a resource which cannot be depleted – the sun. Ethanol is created through the photosynthesis process, which causes a feedstock such as sugar cane or maize to grow. These feedstocks are then processed into ethanol. The table below outlines some of the primary advantages and disadvantages of ethanol as a fuel:

Advantages Disadvantages Relatively non-toxic The carbon dioxide released when

ethanol is burned is balanced by the carbon dioxide captured when the crops are grown to make ethanol.

Ethanol is produced domestically, which reduced the cost of international import.

Renewable energy source – produced from agricultural crops, particularly grains, which are abundant.

Moderate flash point – this is not particularly ideal, nor is it particularly undesirable.

Relatively inexpensive to produce, however this benefit is outweighed by the high transportation cost.

Ethanol reduces the amount of carbon monoxide and other ground-level toxic air pollutants as compared to gasoline by approximately 10% - 30%.

Low bond dissociation energy – little energy is required to break

Ethanol can form an explosive vapour in fuel tanks. However, in accidents, ethanol is less dangerous than gasoline because it has a very low evaporation speed, which keeps the alcohol concentration in the air low and non-explosive.

Ethanol is already in a partially oxidised state, since it contains an oxygen atom and therefore, it gives off significantly less energy on combustion than petrol.

Relatively low energy density – this means that the fuel gives off less energy upon combustion

Heat of combustion is equal to -1227 kJ/mol-1 – this is relatively low compared to the heat of combustion for other fossil fuels, such as petrol.

Issues with transportation is gasoline pipelines

Use of ethanol can lead to long-term corrosion of engines, which ultimately causes damage to the vehicle.

the bonds and therefore, the compound combusts relatively easily; however, due to its low energy density, the fuel releases less energy than petrol.

Ethanol is only available in limited areas

Energy-intensive production – corn-based ethanol production can use almost as much energy to produce as it supplies.

Ethanol is very expensive in comparison to its standard fuel competition, with it costing three times as much to produce as gasoline.

Unfortunately, current agricultural practices depend heavily upon petroleum-based fertilisation, which therefore undercuts the value of ethanol as a fuel alternative.

Production of ethanol uses a very large amount of water (approximately 11 – 22 litres are required to produce 4 litres of ethanol)

Vehicle systems would have to be adapted for use of ethanol as a fuel.

3. Propane (Liquid Petroleum Gas) (C3H8)

Propane or Liquid Petroleum Gas (LPG) is a clean-burning fossil fuel which can be used to power internal combustion engines in motor vehicles. The table below outlines the key advantages and disadvantages of LPG as a fuel.

Advantages Disadvantages Non-toxic Non-corrosive – leads to longer

engine life High octane rating – not very

prone to ‘knocking’ Free of additives such as

tetraethyl lead Burns more cleanly than petrol Up to 50% less expensive than

petrol Simple molecular structure allows

fuel to burn more completely in an internal combustion engine, so that less carbon monoxide, soot

Lower energy density than petrol or other standard fuel competition due to the simplicity and low molecular weight of the molecule, and therefore, it releases significantly less energy upon combustion.

Lower enthalpy of combustion than petrol – less energy is released, therefore the mileage is reduced

Not all automobile engines are suitable for use with LPG as a fuel.

Limited availability Very low flash point (-104℃) – this

and unburned hydrocarbons are released into the atmosphere

The bond dissociation energy of the carbon-hydrogen bonds found in propane is approximately 423 kilojoules per mole. The carbon-carbon bonds have bond dissociation energies of approximately 372 kilojoules per mole. This means that a relatively small amount of energy is required to break the bonds, which means the activation barrier is quite low and the fuel combusts quite easily.

Low molecular weight makes it easy to store and transport

means that the fuel is highly flammable

Potentially hazardous to human health and safety – can act as a simple asphyxiant, meaning that at high concentrations, it replaces the oxygen in the air, making it impossible to receive the oxygen needed for breathing.

Commercially available LPG is currently derived from fossil fuels. Burning LPG released carbon dioxide into the atmosphere, and does contribute to global warming (approximately 160kg of carbon dioxide is released into the atmosphere per 100L of LPG). However, LPG releases less CO2 per unit of energy than petrol or other fossil fuels.

The initial cost of converting vehicles to LPG can be up to $3000

Although each of the fuels analysed in the tables above have several disadvantages as fuel sources, they can each certainly play a role in reducing dependence upon fossil fuels and should be seriously considered as alternative fuel sources to petrol.

d.) Produce a briefing document for the Federal Government which links the suitability of fuels with their physical and chemical properties for one replacement and justify your choice based on the evidence. What further information/research would be required before making a final decision?

With the increasing concern about global warming and fossil fuel supplies, it is crucial that the government turn their attention to researching and switching to alternative fuel sources in order to counter the situation. Despite the fact that petrol has been used as the primary fuel source for automobiles for decades, it has a very drastic impact upon the environment, which outweighs its effectiveness as a fuel. This document will briefly outline the advantages and disadvantages of petrol as a fuel source and will propose a suitable replacement for it.

Petrol

Petrol, also known as petroleum is a transparent, flammable liquid which is used primary as a fuel in internal combustion engines and is derived from crude oil. It is made up of a complex array of hydrocarbons and enhanced with a number of additives. As it is a mixture, petrol has no exact chemical formula, but it is usually primarily composed of iso-octane (C8H18) and its various isomers. The table below outlines some of the key advantages and

disadvantages of petrol as a fuel, with regards to its chemical and physical properties as well as its production and ease of use.

Advantages Disadvantages High availability Even with the rapidly increasing

cost, it is still one of the cheapest fuels

High energy density – a large amount of energy is stored within the fuel, therefore it releases a significant amount of energy upon combustion (exothermic reaction)

High enthalpy of combustion – great deal of energy is released during combustion

The finding, extraction, refinement and sale of petrol has created millions of jobs across the world (Hinckley, M, 2012)

Highly combustible, yet stable due to the long hydrocarbon chains

Relatively high octane rating, however not as high as LPG

Moderate viscosity

The increased use and dependence upon petrol has resulted in a drastic increase in the greenhouse gas and CO2 emissions into the atmosphere, as well as pollution in the water and air. Petrol produces significantly more greenhouse gases than diesel or LPG

There supply of fossil fuels on earth is rapidly diminishing

The price of petrol is expected to continue to rise as oil reserves dry up

Crude oil spills can have severe impacts upon the environment

Disagreeable odour Petrol contains some additives,

which result in the release of unburned carbon, carbon monoxide (CO) and other potentially hazardous waste products

As can be discerned from the information listed in the table above, the disadvantages of petrol as a fuel source outweigh the benefits and will not be effective for very much longer with the dwindling supply of fossil fuels and also, the need to reduce CO2 emissions. The graph below shows that fossil fuels are the primary contributor to global warming and their use has drastically increased over the past fifty years. If alternative fuels are not immediately sought out, these emissions are expected to continue to rise, posing severe risks to both human health and safety and the environment.

Figure 1: This graph represents the increase in the use of fossil fuels over the years.

Alternative to Petrol: Hydrogen (H2)

As a possible alternative to petrol, hydrogen fuel is one of the most promising fuel sources. As with all fuels, there are several drawbacks; however, with some development of technology, the prospect of switching to hydrogen fuel altogether and reducing CO2 and greenhouse gas emissions significantly is possible.

Hydrogen fuel is the lightest and simplest fuel and poses minimal risks to the environment. Furthermore, it possesses several desirable properties which make it an ideal replacement for petrol. To begin with, since hydrogen is the most abundant element on earth, with over 70% of the earth’s surface being covered in water, it is readily available and would not be exhausted, unlike fossil fuels. In addition to this, hydrogen fuel produces only water as a by-product, rather than carbon-based emissions or other potentially harmful pollutants, making it very environmentally friendly. Hydrogen also has one of the highest energy densities of all (143, 000 KJ kg-1), which means that a great deal of energy is stored within the compound and therefore, it releases a large amount of energy upon combustion. This is very desirable for motor vehicles, as a high energy density results in increased mileage. For this reason, Hydrogen is a better alternative than biofuels such as Ethanol or LPG, which have much lower energy densities. Also, this high energy density is one of the reasons why hydrogen is used for rocket fuel in outer space.

However, the principal disadvantage of hydrogen fuel is that a great deal of energy must be supplied in order to extract it from hydrogen-containing compounds, as it does not occur in a natural form. This process is often very expensive, which leads to increased prices of the fuel. Ironically, in order to produce hydrogen fuel, fossil fuels such as oil and coal are often used, either to provide electricity to separate the hydrogen from water through the process of electrolysis, or as the substance from which the hydrogen is extracted. For this reason, the environmental benefits of hydrogen as a fuel are almost completely cancelled out by the use of fossil fuels in its production. Furthermore, hydrogen is naturally a gas, making it extremely difficult to store in a liquid state. A very large amount of energy would need to be supplied in order to compress the fuel and special containers would have to be manufactured for the sole purpose of storing hydrogen fuel. Also, hydrogen is extremely flammable, with the same self-ignition temperature as methane and therefore, has a very low octane rating.

Despite these disadvantages, if fuel technology continues to advance, hydrogen could soon be considered as an alternative to petrol. However, in order for it to be considered as a widely-used fuel, the issue of hydrogen fuel production must be resolved to minimise, or eliminate completely the use of fossil fuels and also, due to hydrogen’s high flammability and reactivity, several procedures would have to be implemented in order to minimise the risk of fire hazards.

Other Information to Consider

Prior to selecting an alternative for petrol, the exact details of production would need to be specified, as well as the cost of production. Internal combustion engines would need to be tested to ensure that the fuel does not corrode or react with any materials present in the system. Furthermore, exact details as to the enthalpies of combustion, bond dissociation energies and environmental impact would need to be confirmed and optimum combustion conditions in the system would need to be ensured.

Annotated Bibliography (Part D)

(n.a). (2006). Energy From Fossil Fuels . Retrieved October 24, 2012, from WOU Education : http://www.wou.edu/las/physci/GS361/Energy_From_Fossil_Fuels.htm

This source is highly relevant to the topic of fuels and contains some very useful information regarding energy densities, combustion of fossil fuels, oxidisation, as well as bond formation and dissociation. The information is very succinct and is presented very effectively, with tables and other non-text inserts. Although the author is unknown, the website is still reasonably credible as it comes from the WOU Education website.

(n.a). (2009). Chemistry of Petroleum . Retrieved October 24, 2012, from Petroleum: http://www.petroleum.co.uk/chemistry/

This website is very concise and provides very relevant, useful information on the topic of petrol's physical and chemical properties and also its composition. However, the credibility of the source is somewhat questionable as both the author and the name of the web site are unknown. Despite this, the information on this website has been verified by other credible sources.

(n.a.). (2007 ). Petrol . Retrieved October 24 , 2012, from Chemistry Daily : http://www.chemistrydaily.com/chemistry/Petrol

This online encyclopaedia entry contains some very useful information regarding the chemical and physical properties of petrol, its environmental impact and also its production and ease of use. The website is reasonably credible as it comes from the online chemistry encyclopaedia Chemistry Daily. Furthermore, all of the information included in the website can be verified by other credible sources.

(n.a.). (2012 ). Pros and Cons fo Hydrogen Fuel Cars . Retrieved October 24, 2012, from eHow : http://www.ehow.com/facts_5004395_pros-cons-hydrogen-fuel-cars.html

This website provides highly concise and specific information about the advantages and disadvantages of hydrogen as a fuel source, with particular attention to its chemical properties, environmental impact and production and ease of use. The information is very easy to interpret and relates directly to the question asked in part d. Furthermore, the website is a credible source as it is proofread and corrected by accredited professionals.

BBC. (n.d.). Hydrocarbons as Fuels . Retrieved October 24, 2012, from GCSE Bitesize : http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/crudeoil/hydrocarbonsrev3.shtml

This website contains very clear specific information about the use of hydrocarbons as fuels, and lists and analyses several alternatives to petrol with regards to their advantages and disadvantages. The website is a very credible source as it is hosted by the British Broadcasting Corporation, as part of an educational support tool called GCSE Bitesize.

College of the Desert. (2001). Hydrogen Properties . Retrieved August 9, 2012, from Hydrogen Fuel Cell Engines and Related Technologies : http://www1.eere.energy.gov/hydrogenandfuelcells/tech_validation/pdfs/fcm01r0.pdf

This document is a highly relevant, succinct source containing a great deal of information relating to the chemical structure and properties of hydrogen as a fuel. The document is a very credible source as it is hosted by an academic institution - the College of the Desert. However, the website is relatively old as it was first published in 2001 and therefore, some of the information and the technologies the document describes are out-dated.

Hinckley, M. (2012). Advantages and Disadvantages of Alternative Fuels. Retrieved October 24, 2012, from eHow : http://www.ehow.com/about_4779842_advantages-disadvantages-alternative-fuels.html

This website is very concise and well-formatted, containing relevant information as to the advantages and disadvantages of alternative fuel sources and compares each of the alternatives to petrol with regards to their chemical and physical properties. Furthermore, the website is a credible source as it is proofread and corrected by accredited professionals.

Martinez, I. (2012). Fuel Properties . Retrieved October 24, 2012, from http://webserver.dmt.upm.es/~isidoro/bk3/c15/Fuel%20properties.pdf

This document is a very credible, recent source which provides an in-depth analysis of the chemical and physical properties of various fuels. It also outlines the key advantages and disadvantages of using hydrogen as an alternative fuel source to petrol. The document is very credible, as it is written by an accredited professional.

U.S. Department of Energy . (2012). Hydrogen . Retrieved October 24, 2012, from Alternative Fuels Data Centre : http://www.afdc.energy.gov/fuels/hydrogen.html

This website provides very detailed information as to the chemical and physical properties of hydrogen in a very concise table form. The source is obviously very credible, as it is hosted by the U.S. Department of Energy.

Bibliography (Parts a, b, c)

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Chemistry ERT (Fuels)