Oil tends to be composed of medium sized molecules, although composition varies greatly from one grade of crude to the next. In general, the denser the oil, the longer the carbon chains in the molecules. Finally coal contains the largest and most complex hydrocarbon molecules.
Since different hydrocarbons have different ratios of hydrogen to carbon, they produce different ratios of water to carbon dioxide. In general, the longer and more complex the molecule, the greater the ratio of carbon to hydrogen. For this reason, combustion of equal amounts of different hydrocarbons will yield different quantities of carbon dioxide, depending on the ratio of carbon to hydrogen in molecules of each. Since coal contains the longest and most complex hydrocarbon molecules, burning coal releases more CO 2 than burning the same mass of oil or natural gas.
This also changes the energy density of each of these fuels. Below is a chart of the CO 2 emitted from the production of Choose a fuel from the drop down menu to see the net reaction that occurs during combustion. Fossil Fuels. Nuclear Fuels. Hydrocarbons Hydrocarbons are chemical compounds that contain the elements carbon and hydrogen only. Fractional distillation Fractional distillation separates the crude oil mixture into a number of smaller, different parts called fractions.
Oil fractions The diagram below summarises the main fractions from crude oil and their uses and the trends in properties. Many different products are obtained from crude oil in a fractionating column As you go up the fractionating column, the hydrocarbons have: lower boiling points lower viscosity they flow more easily higher flammability they ignite more easily This means that in general hydrocarbons with small molecules make better fuels than hydrocarbons with large molecules.
National 4 Subjects National 4 Subjects up. Hydrocarbons are the critical energy storage molecules within all major types of fossil fuels including coal, oil, and natural gas and biofuels. They also form the feedstock for the production processes of many types of plastics. If there is too much carbon or too little oxygen present when hydrocarbons are burned, carbon monoxide CO may also be emitted.
Sometimes unburned hydrocarbons are released into the air during incomplete combustion. Burning fossil fuels, including gasoline in automobile engines, releases some hydrocarbons into the air.
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