C2: Fossil Fuels
There are three main fossil fuels: coal, gas and crude oil. Coal is the most abundant but crude oil, also known as petroleum, is the most important. However, petroleum is difficult to use in its natural form. Petroleum contains a mixture of hydrocarbons of varying lengths. Long chain hydrocarbons are stronger intermolecular forces than short chain hydrocarbons. As a result, boiling points can be used to separate crude oil into fractions of varying chain lengths. At oil refineries, the fractions are separated by fractional distillation.
First image courtesy of the Pearson text. Second image comes from the Oxford text.
The more volatile short chain hydrocarbons make better fuels and burn cleaner. However, there are more long chain hydrocarbons in crude oil than short ones. In order to get more short chains, a process called cracking is used. This process is extremely important in the production of gasoline and diesel fuel.
Catalytic reforming is used to convert low-octane numbered alkanes such as heptane or octane into higher-octane numbered isomers such as methylbenzene or 2,2,4-trimethylpentane. I strongly suggest watching Mr. Thornley's YouTube videos on cracking and reforming petroleum.
The production of energy by burning fuels produces carbon dioxide. The carbon foot print of a reaction is a measure of the net quantity of carbon dioxide produced by the process. Even though biofuels may cost more to produce, their carbon footprint is less because carbon dioxide is absorbed by photosynthesis while the fuel is growing.
Be sure to examine the worked problems in the textbook.