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Crude oil is separated by a process called fractional . Crude oil is heated to around 400 degrees celsius to turn all the hydrocarbons to gases. The gas is then passed into a fractional distillation where the gases rise up cool and to liquid at their boiling points. Some have boiling points so condense lower down, while those with lower boiling points up the column. Some stay as even at the top of the column. Each substance is a mixture of with similar boiling points called a fraction.
The hydrocarbons of each fraction have boiling points as the molecules in that fraction are all a similar size - they have a similar number of and hydrogen atoms. There are forces between molecules which hold them together. Force is needed to separate these molecules. When heated, the molecules gain until they have enough energy to overcome the forces holding them together and the molecules become a .
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