I've done C1 last yr but an answer: Cracking allows large hydrocarbon molecules to be broken down into smaller, more useful hydrocarbon molecules. Fractions containing large hydrocarbon molecules are heated to vaporise them. They are then either:
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- passed over a hot catalyst, or
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- mixed with steam and heated to a very high temperature.
These processes break chemical bonds in the molecules, causing thermal decomposition reactions. Cracking produces smaller alkanes and alkenes (another type of hydrocarbon).
Fractional distillation of air, air cooled, different gases have different boiling points so condense at different areas of collum, splitting up the air.