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According to Lyons a fuel can be defined as a compound that is consumed by the process of oxidation to release its stored energy. The energy in fuels is trapped in the chemical bonds through the process of photosynthesis and respiration. The form of oxidation that is most common is the direct reaction between a fuel and oxygen during combustion. In chemical terms, fuels are comprised of carbon and hydrogen atoms which are bonded together into hydrocarbon molecules. Some examples of fuels include methane gas or natural gas, petrol, diesel, and kerosene. Fuels like methane and kerosene are useful at many homes for lighting and cooking since their combustion can be controlled, while diesel, and petrol are usually used in internal combustion engines for example those used in automobiles and factory engines.
According to Chandra Methane gas is referred to as a chemical compound that is formed by decaying of animal and plant matter. It is known as the major component of natural gas which is a nonrenewable fuel that is mined underground. By itself, methane is a colorless, tasteless, and odorless gas that is regarded as a perpetual source of natural gas because it is formed from the decaying matter. The decomposition of animal and plant matter is done by bacteria in the absence of oxygen or any other substance such as nitrate, which do not accept electrons. Methane gas is a widely used source of energy that is very efficient and friendly since it makes use of the organic waste that would otherwise pollute the environment. The chemical formula for methane gas molecules constitute a one carbon atom surrounded by four hydrogen atoms and is represented as CH4. The hydrogen atoms are covalently bonded to the central carbon atom. The obligate anaerobes convert the mixture of hydrogen gas and carbon dioxide gas into methane gas and water. These methane bacteria contain coenzymes which help in the process of conversion. Methane bacteria are also found in the alimentary canal of cows specifically in the rumen, where they combine carbon dioxide gas and hydrogen gas that are made available by the anaerobic gut bacteria. The following is the chemical equation regarding the chemical combination of carbon dioxide gas and hydrogen gas.
CO2 + 4H2 CH4 + 2H2O ∆ Go = -31kcal/mole
As can be seen from the above equation, the reaction of combining carbon dioxide and hydrogen gas is accompanied with the release of energy. When the resultant compound, that is, methane is subjected to heat in the presence of oxygen, the covalent bonds are broken down to release the energy of bonding. According to Chandra Combustion of methane is highly exothermic as can be represented by the chemical equation below.
CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (l) ∆ H = -891kJ
The energy release due to combustion of methane gas is usable directly in heating and lighting homes, and in commercial buildings (Chandra 115). Methane gas can also be used in electric power generation.
Gasoline or Petrol is a mixture of liquid hydrocarbons that is formed mainly from crude petroleum and that is used in the internal combustion engines as a fuel. The liquid is characteristically volatile and highly flammable making it a valuable fuel for most machines. Gasoline is the most preferred fuel for the internal combustion engines since it releases lots of energy during combustion. This fuel readily mixes with oxygen while in a carburetor and therefore ensures that almost all gasoline undergoes complete combustion to avoid wastage and atmospheric pollution. Partially burnt fuels produce a lot of soot due to the unburned carbon and therefore can pollute the atmosphere. As compared to a fuel like methane gas which is comprised of simple and specific hydrocarbons, gasoline is comprised of a variety of complex hydrocarbons. The molecules of gasoline are large and constitute many branches hence looking more complex. The number of carbon atoms varies with different molecules within gasoline.
According to Brown, gasoline is made available due to catalytic cracking of crude oil in the process of oil refining. The process involves the use of a catalyst, increased pressure, and high temperature. Platinum, aluminum, and processed clay are the catalysts which are added to crude petroleum to accelerate the breakdown of larger hydrocarbon molecules into smaller hydrocarbon molecules. Polymerization is another process that is used to make gasoline and is the direct opposite of cracking. It involves combining the smaller hydrocarbon molecules of gaseous fuels into larger hydrocarbon molecules forming a liquid fuel. These large hydrocarbon molecules are usually alkanes with the number of carbon atoms varying from four to twelve, for instance butane, octane, hexane, and heptanes with four, eight, six, and seven carbon atoms respectively. The carbon atoms are covalently bonded to one another and to the hydrogen atoms. These molecules can be represented chemically as follows:
Butanes = CH3CH2CH2CH3,
Octane = CH3CH2CH2CH2CH2CH2CH2CH3,
Hexanes = CH3CH2CH2CH2CH2CH3,
Heptanes = CH3CH2CH2CH3
The combination of alkane chains with carbon atoms ranging between four carbon atoms to twelve carbon atoms result into gasoline. Combustion of gasoline in the internal combustion engines can be represented as burning heptanes, octane, butane and others. The chemical representation is as follows:
2C8H18 (l) + 25O2 (g) 16CO2 (g) + 18H2O (l) ∆cHᶿ298 = -5074.2kJ/mole
From the above equation it is apparent that combustion of long chained alkanes that make up gasoline is very exothermic and can release extremely large amounts of heat. Even if the properties of each type of alkane in the gasoline fuel, the trends on physical and chemical properties are similar.