# Describe how steam cracking is used to produce smaller, more useful molecules from crude oil fractions, and explain why alkenes produced during cracking are described as unsaturated.

> OCR GCSE Chemistry A: Gateway Science (J248) — C6.2 Organic chemistry · Describe · 4 marks

> Crude oil is a finite resource that contains a mixture of hydrocarbons. Many of the larger hydrocarbon molecules obtained from crude oil have limited uses, so they are processed to produce more useful products.

## Mark scheme (4 marks)

1. Steam cracking involves heating long-chain hydrocarbons to high temperatures (with steam)
2. The large/long-chain hydrocarbon molecules are broken down / split into smaller hydrocarbon molecules
3. Alkenes contain a carbon–carbon double bond (C=C)
4. Unsaturated means the molecule contains fewer hydrogen atoms than the maximum possible / does not contain the maximum number of hydrogen atoms (due to the double bond)

## Key terms

- [cracking](https://www.gradenine.co.uk/glossary/cracking)
- [steam cracking](https://www.gradenine.co.uk/glossary/steam-cracking)
- [alkenes](https://www.gradenine.co.uk/glossary/alkenes)
- [unsaturated](https://www.gradenine.co.uk/glossary/unsaturated)
- [crude oil](https://www.gradenine.co.uk/glossary/crude-oil)

## Related

- [Revision notes for OCR GCSE Chemistry A: Gateway Science (J248)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-how-steam-cracking-is-used-25703852) · Published by Druglandscape Ltd.