# Ethene (C₂H₄) is an alkene produced during the cracking of long-chain hydrocarbons. Ethene can react with bromine water and can also be used to make poly(ethene). Explain why ethene is described as an unsaturated hydrocarbon, and describe what happens when ethene reacts with bromine water, including the type of reaction that occurs.

> Eduqas A-Level Chemistry — 2.4 Organic compounds · Explain · 5 marks

## Mark scheme (5 marks)

1. Ethene is a hydrocarbon because it contains only carbon and hydrogen (atoms/elements)
2. Ethene is unsaturated because it contains a carbon–carbon double bond (C=C)
3. Bromine water changes from orange/brown to colourless when ethene is added
4. The double bond opens/breaks and bromine adds across the double bond
5. This type of reaction is called an addition reaction

## Key terms

- [unsaturated](https://www.gradenine.co.uk/glossary/unsaturated)
- [hydrocarbon](https://www.gradenine.co.uk/glossary/hydrocarbon)
- [bromine water](https://www.gradenine.co.uk/glossary/bromine-water)

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- [Revision notes for Eduqas A-Level Chemistry](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/ethene-c-h-is-an-alkene-produced-f54754be) · Published by Druglandscape Ltd.