# Explain why chlorine is more reactive than bromine, and predict what would be observed when chlorine water is added to a solution of potassium bromide.

> AQA A-Level Chemistry (7405) — 3.2.3 Group 7(17), the halogens · Explain · 5 marks

> The halogens in Group 7 react by gaining one electron to form a negative ion. Their reactivity decreases down the group.

## Mark scheme (5 marks)

1. Chlorine atoms are smaller than bromine atoms (or chlorine has fewer electron shells than bromine)
2. The incoming electron is attracted more strongly to the nucleus in chlorine (or the nucleus has a greater attraction for the gained electron in chlorine)
3. Chlorine displaces bromine from the potassium bromide solution (a displacement reaction occurs)
4. The solution turns orange / brown (bromine is produced)
5. The ionic equation / word equation shows chlorine reacting with potassium bromide to form potassium chloride and bromine (or correct reference to Cl₂ + 2KBr → 2KCl + Br₂)

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](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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