4th Nov '25

Cracking

Long hydrocarbon are useful than shorter ones like petrol. We can 'crack' these longer chains into shorter ones.

In the exam use the chemical symbols to represent atoms rather than circles eg:

This process involves heating the hydrocarbons to vaporise them and passing the vapours over a hot catalyst. A catalyst is a chemical that speeds up a reaction without being used up or changed itself and allows the reaction to happen at a cooler temperature.

The actual cracking process is a thermal decomposition reaction in which a molecule splits into molecules, when . In the lab, cracking can be done using the following equipment:

Click here for full method

In this example the porcelain chips are the .

When we do this we end up with a mixture of both alkanes and alkenes (see What's in crdue oil? from C1a).

The alkanes are used as , while the alkenes can also be used to make (plastics).