# Propene (C₃H₆) is an alkene. Explain why propene is described as an unsaturated hydrocarbon and describe what happens when propene undergoes an addition reaction with hydrogen.

> WJEC A-Level Chemistry (Wales) — 2.5 Hydrocarbons · Explain · 5 marks

## Mark scheme (5 marks)

1. Propene contains a carbon-to-carbon double bond (C=C)
2. Unsaturated means the molecule is not joined to the maximum number of hydrogen atoms / does not contain only single bonds
3. In the addition reaction, hydrogen adds across the double bond
4. The double bond becomes a single bond / the product is saturated
5. The product formed is propane (C₃H₈)

## Key terms

- [unsaturated](https://www.gradenine.co.uk/glossary/unsaturated)
- [addition reaction](https://www.gradenine.co.uk/glossary/addition-reaction)
- [alkene](https://www.gradenine.co.uk/glossary/alkene)

## Related

- [Revision notes for WJEC A-Level Chemistry (Wales)](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/propene-c-h-is-an-alkene-explain-3819d7ef) · Published by Druglandscape Ltd.