Fuels
 Coal, natural gas, petroleum are fossil fuels
 Main constituent of Natural gas is methane
 Crude oil/Petroleum is a complex mixture of a very large number of
compounds most of which are hydrocarbons, molecules composed of
hydrogen and carbon atoms only.
 Different fractions of crude oil can be separated by fractional distillation.
 The crude oil is evaporated and its vapours condense at different
temperatures in the fractionating column.
 Up the fractioning column the temperature gradually decreases
(temperature gradient), so the highest boiling (least volatile) molecules
tend to be at the bottom and the lowest boiling (most volatile)
hydrocarbons go to the top. The rest of the hydrocarbon molecules then
condense out in narrow temperature range i.e. the different fractions
condense out in a gradual way from top to bottom depending on their
boiling point.
 So all of the hydrocarbon molecules separate out according to their
boiling/condensation point.
 The bigger the molecule, the greater the intermolecular attractive forces
between the molecules, so the higher the boiling point or condensation
point
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