# Alkanes are used as fuels. Explain why cracking is carried out on long-chain alkanes and describe what happens during catalytic cracking.

> AQA A-Level Chemistry (7405) — 3.3.2 Alkanes · Explain and Describe · 5 marks

## Mark scheme (5 marks)

1. There is greater demand for shorter-chain hydrocarbons (as fuels) than for longer-chain hydrocarbons
2. Shorter-chain alkanes are more flammable / burn more easily, making them better fuels
3. Long-chain hydrocarbons are heated to vaporise them
4. The vapour is passed over a hot powdered aluminium oxide catalyst
5. The long-chain molecules split apart (on the surface of the catalyst) to form smaller molecules, including alkenes

## Key terms

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

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain and Describe" 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/alkanes-are-used-as-fuels-explain-6303c38b) · Published by Druglandscape Ltd.