3(c) Reversible reactions and equilibria
Pearson Edexcel International GCSE Chemistry · 4CH1
Paper 2 | Whole paper: All content including bold C statements
Reactions that go both ways, dynamic equilibrium, and predicting which way a change pushes them.
Specification coverage
Topic 3 Physical chemistry (c) Reversible reactions and equilibria — statements 3.21–3.28C (includes bold C statements assessed on Paper 2 only)
Assessment objectives: AO1, AO2. Suggested learning time: 70 minutes.
Required knowledge
- Reversible reactions and the meaning of dynamic equilibrium
- The effect of changing temperature, pressure and concentration on the position of equilibrium
- The Haber process: conditions used and the reasons for the compromise
- Bold C statements: the contact process and further equilibrium applications
Required skills
- Predict the direction of shift for a given change
- Explain why industrial conditions are a compromise between yield and rate
How it is examined
- Multiple-choice and short-answer recall
- Application of the content to an unfamiliar context
- Extended open-response, marked on the quality of a connected explanation
Common mistakes
- Describing equilibrium as 'the reaction stopping'. Both reactions continue at equal rates — that is what dynamic means.
- Saying equilibrium means equal amounts of reactants and products. It means equal rates, not equal quantities.
- Explaining the Haber conditions only by yield. The chosen temperature is a compromise: a higher temperature lowers yield but raises rate.