# Alkenes are produced during the cracking of crude oil fractions. Describe the differences between alkanes and alkenes, and explain why alkenes are considered more useful products of cracking than the long-chain alkane molecules they are made from.

> Edexcel GCSE Chemistry (1CH0) — 8.1 Fuels · Describe and Explain · 4 marks

## Mark scheme (4 marks)

1. Alkanes have the general formula CₙH₂ₙ₊₂, whereas alkenes have the general formula CₙH₂ₙ
2. Alkenes contain a carbon–carbon double bond / are unsaturated, whereas alkanes do not / are saturated
3. Alkenes are used as monomers / to make polymers (plastics), so there is high industrial demand for them
4. Long-chain alkanes are less useful / in less demand because they are too viscous / have too high a boiling point, whereas smaller molecules produced by cracking are in greater demand (e.g. as fuels or chemical feedstocks)

## Key terms

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

## Related

- [Revision notes for Edexcel GCSE Chemistry (1CH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and 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/alkenes-are-produced-during-the-cracking-1063e136) · Published by Druglandscape Ltd.