# Ethene reacts with hydrogen bromide gas to form bromoethane. Describe what happens during this reaction and explain why ethene is able to undergo this type of reaction whilst ethane cannot.

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

> Ethene (C₂H₄) and ethane (C₂H₆) are both small hydrocarbons, but they react very differently with hydrogen bromide gas.

## Mark scheme (4 marks)

1. Ethene undergoes addition reaction / hydrogen bromide adds across the double bond
2. The product formed is bromoethane (CH₃CH₂Br)
3. Ethene has a carbon–carbon double bond (C=C) which can open / break
4. Ethane has only single bonds (C–C) / is saturated so cannot undergo addition reactions

## Related

- [Revision notes for Cambridge International IGCSE Chemistry (0620)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/ethene-reacts-with-hydrogen-bromide-gas-b72b5b39) · Published by Druglandscape Ltd.