Long alkanes are generally not very useful. They don’t burn well and, like other alkanes, have limited reactions other than burning.

Thankfully there is a reaction that converts these less useful long chains into more useful compounds and is called cracking. It involves breaking down longer alkane chains with heat and a catalyst. When this takes place this usually forms a slightly shorter alkane and an alkene. For example

Decane –> Octane + Ethene
C10H22 –> C8H18 + C2H4



Apparatus for cracking hydrocarbons Fig. 1


This is similar to other reactions you may have seen as it is another example of a thermal decomposition reaction. The difference is that this time you need a catalyst to help break apart the alkanes.

A cracking practical can be carried out in a school lab quite easily by using a broken pottery as a catalyst. Figure 1 shows you how it can be set up.

The worksheet can also be found by clicking on the worksheet below.

Cracking hydrocarbons

This is a dangerous scientific experiment and must not be attempted without skilled supervision. You must also carry out your own risk assessment. Please consult CLEAPSS or similar agencies before undertaking such experiments.