Halogen Displacement Reactions

This lesson covers halogen displacement reactions, a key topic in the Edexcel GCSE Chemistry specification (1CH0), Topic 6: Groups in the Periodic Table. You need to understand that a more reactive halogen will displace a less reactive halogen from a solution of its salt, and you must be able to describe the observations and write equations for these reactions.

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The Principle of Halogen Displacement

A more reactive halogen can displace a less reactive halogen from an aqueous solution of its halide salt. This is because the more reactive halogen is better at gaining electrons than the less reactive one — it is a stronger oxidising agent.

The general pattern is:

more reactive halogen + metal halide → metal halide (of more reactive halogen) + less reactive halogen

This is very similar to the displacement reactions of metals, but instead of metals competing to lose electrons, halogens compete to gain electrons.

Exam Tip: Displacement reactions prove the order of reactivity. If chlorine can displace bromide ions from a solution, it proves chlorine is more reactive than bromine. This is the experimental evidence for the reactivity trend.

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The Displacement Experiment