# Ethene (C₂H₄) is an alkene produced during the cracking of long-chain hydrocarbons. Explain why ethene is described as unsaturated and describe how ethene can undergo addition polymerisation to form poly(ethene).

> Edexcel A-Level Chemistry (9CH0) — 6.3 Alkenes · Explain · 5 marks

> Ethene is the simplest alkene. It is produced in large quantities by the petrochemical industry and is an important feedstock for making plastics.

## Mark scheme (5 marks)

1. Ethene is unsaturated because it contains a carbon-to-carbon double bond (C=C)
2. The double bond can open / break to allow ethene molecules to join together
3. Many ethene monomers join together (in a chain)
4. No other substance / no small molecule is produced / it is an addition reaction
5. The product is poly(ethene) / a long-chain polymer with repeating –CH₂CH₂– units

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](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/ethene-c-h-is-an-alkene-produced-2f29bfa2) · Published by Druglandscape Ltd.