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.
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.
