Hydrocarbon

Define a hydrocarbon as a molecule containing hydrogen and carbon atoms only. The word ‘only’ excludes compounds containing other elements.

A fraction is a mixture of hydrocarbons with similar numbers of carbon atoms, not a single pure compound.

For catalytic cracking, describe vaporising the hydrocarbon and passing its vapour over a hot catalyst. For steam cracking, describe mixing the vapour with steam and heating to a very high temperature.