# Ethene is produced industrially by the cracking of long-chain hydrocarbons. Explain why ethene is described as an unsaturated hydrocarbon and describe one addition reaction that ethene can undergo to form a saturated product.

> Cambridge International IGCSE Chemistry (0620) — 11.5 Alkenes · Explain · 4 marks

## Mark scheme (4 marks)

1. Ethene is unsaturated because it contains a carbon–carbon double bond (C=C)
2. Unsaturated means the molecule does not contain the maximum number of hydrogen atoms (i.e. not all single bonds between carbons)
3. Correct identification of a valid addition reaction, e.g. ethene reacts with hydrogen (hydrogenation) to form ethane, OR ethene reacts with water (steam) to form ethanol, OR ethene reacts with bromine to form dibromoethane
4. The product is saturated because the double bond has broken and the two new atoms / groups are added across it, so all carbon–carbon bonds are now single bonds

## Key terms

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

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Source: [GradeNine](https://www.gradenine.co.uk/q/ethene-is-produced-industrially-by-the-380953e0) · Published by Druglandscape Ltd.