Pearson Edexcel International GCSE Chemistry · specification 4CH1 · Paper 2 | Whole paper: All content including bold C statements · Free · no account needed
3(b) Rates of reaction (4CH1 specification)
What changes a reaction's speed, explained by collisions — and the practicals that measure it.
Learn it on Incandio
The 5 Incandio pages that teach this — each explained in full, then proved in marked questions, taught back to an AI pupil and defended in a debate. Completely free.
- Rates of Reaction — Four things that make a reaction faster, and two ways of measuring whether they did.
- Collision Theory — One explanation that accounts for every factor on the previous page.
- Catalysts — A substance that speeds a reaction up, takes part in it, and is there unchanged at the end.
- Reversible Reactions — Reactions that run both ways, and two you can drive backwards and forwards at will.
- Dynamic Equilibrium — Nothing appears to be happening, everything is still happening — and that is what lets conditions shift it.
The teaching route this belongs to: Topic 3 · Physical chemistry (Chemistry) — the lessons in order, with every gate.
Specification coverage
Topic 3 Physical chemistry (b) Rates of reaction — statements 3.11–3.20C (includes bold C statements assessed on Paper 2 only)
Assessment objectives: AO1, AO2, AO3. Suggested learning time: 90 minutes.
Required knowledge
- The effect of surface area, concentration, temperature, pressure and catalysts on the rate of reaction
- Collision theory as the explanation for each factor
- The action of a catalyst in providing an alternative pathway of lower activation energy
- Bold C statements: interpretation of rate graphs and calculation of rate in greater depth
Required skills
- Explain each factor by frequency of collisions and energy of collisions
- Interpret a rate graph, including gradient and plateau
- Design a fair investigation of one rate factor
- Describe and evaluate the required practical: Investigate the effect of changing the surface area of marble chips and the concentration of hydrochloric acid on the rate of reaction, and the effect of temperature on the reaction between sodium thiosulfate and hydrochloric acid.
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
- Practical questions on method, variables, data and sources of error
Common mistakes
- Explaining the effect of temperature only as 'more collisions'. Higher temperature also means a greater proportion of collisions exceed the activation energy, and that is the larger effect.
- Saying a catalyst 'lowers the activation energy of the reaction'. It provides an alternative pathway with a lower activation energy and is not used up.
- Reading a rate graph's plateau as the reaction stopping because of temperature rather than because a reactant is used up.
This page maps the specification. The pages above teach it, and the Chemistry lessons hold the whole course — completely free.