Cracking is an important industrial process used in the oil refinery industry. Explain why cracking is carried out and describe what happens during the cracking of a long-chain alkane molecule.

Cracking is carried out because there is a greater demand for shorter‑chain hydrocarbons, such as gasoline and diesel, than for the long‑chain molecules that are obtained from crude oil. The process breaks the long‑chain alkane into shorter molecules, which are more useful as fuels and feedstocks.

During cracking a long‑chain alkane is subjected to a very high temperature (typically 450–750 °C). The heat causes the C–C bonds to break, producing a mixture of products. The reaction can be carried out either with a catalyst (e.g. alumina, silica or a zeolite) or without a catalyst in a steam‑cracking unit. The main products are a shorter‑chain alkane and an alkene – the latter contains a C=C double bond.

Thus, cracking uses high temperature (and often a catalyst) to thermally decompose long‑chain alkanes into shorter alkanes and alkenes, meeting the market demand for these more valuable hydrocarbons.