# Explain why alkenes are produced during cracking and describe how you could distinguish an alkene from an alkane using a simple chemical test.

> AQA GCSE Chemistry (8462) — 4.7.1 Carbon compounds as fuels and feedstock · Explain · 4 marks

## Mark scheme (4 marks)

1. Cracking involves breaking down long-chain hydrocarbons into smaller molecules / thermal decomposition occurs
2. The smaller molecules produced include unsaturated hydrocarbons / alkenes have at least one carbon-carbon double bond
3. Add bromine water to both substances / shake each substance with bromine water
4. Bromine water turns from orange to colourless with the alkene but remains orange with the alkane

## Key terms

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

## Related

- [Revision notes for AQA GCSE Chemistry (8462)](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/explain-why-alkenes-are-produced-during-dbe6707a) · Published by Druglandscape Ltd.