# Cracking is used to convert large hydrocarbon molecules into smaller, more useful ones. One product of cracking is propene. Explain why cracking is carried out in industry and describe the two methods by which cracking can be done.

> AQA A-Level Chemistry (7405) — 3.3.4 Alkenes · Explain · 5 marks

## Mark scheme (5 marks)

1. There is greater demand for shorter-chain hydrocarbons (as fuels / for making other chemicals) than for longer-chain hydrocarbons
2. Shorter-chain hydrocarbons are more flammable / better fuels OR alkenes produced can be used to make polymers / other chemicals
3. In catalytic cracking, the long-chain hydrocarbons are heated to vaporise them
4. In catalytic cracking, the vapour is passed over a hot powdered aluminium oxide catalyst
5. In steam cracking, the hydrocarbon vapour is mixed with steam and heated to a very high temperature

## Key terms

- [cracking](https://www.gradenine.co.uk/glossary/cracking)

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/cracking-is-used-to-convert-large-19d1de13) · Published by Druglandscape Ltd.