Cracking and Alkenes

Crude oil is a complex mixture of hydrocarbons. Two types of hydrocarbons are alkanes and alkenes.

  • Alkanes are saturated hydrocarbons, which means that there are no double bonds in the structure. There are only single covalent bonds between the carbon atoms. The general formula for alkanes is CnH2n+2
  • Alkenes are unsaturated hydrocarbons, which means that there is at least one double or triple bond between two carbon atoms. The general formula for alkenes is CnH2n

Shorter hydrocarbons tend to be more useful than longer ones, so, longer-chain hydrocarbons undergo a process called cracking to make them shorter.

Cracking is the process of breaking down long-chain saturated hydrocarbon molecules into smaller, more useful molecules. One example of this is the cracking of decane into octane and ethene.

Two methods for carrying out cracking are:

  • Catalytic cracking – This involves using a high temperature and a catalyst to speed up the reaction.
  • Steam cracking – In this method, hydrocarbons are mixed with steam and heated to a high temperature, but without the use of a catalyst.

Cracking is important because there is a higher demand for shorter-chain hydrocarbons. As shorter hydrocarbons are more flammable, they are more effective as fuels than longer-chain hydrocarbons. For example, cars require fuel that burns quickly, allowing it to change speeds rapidly (within a short period of time).