Ethene is produced when long-chain hydrocarbons from crude oil are cracked. Explain why cracking is carried out in industry and describe the conditions needed for steam cracking.

Cracking is carried out because there is a higher demand for shorter‑chain hydrocarbons such as ethene, which are used as fuels and as feed‑stocks for polymers. By breaking long‑chain hydrocarbons into smaller, more useful molecules, the process increases the yield of valuable products.

In steam cracking the long‑chain hydrocarbon is first vapourised and mixed with steam. The mixture is then heated to a very high temperature (typically 750–900 °C) which causes thermal decomposition of the hydrocarbon chains.

The high temperature and presence of steam prevent the formation of coke and promote the formation of alkenes such as ethene.