What does Edexcel GCSE Chemistry Topic 7 cover?

Topic 7 covers the rate of reaction and collision theory, how concentration, pressure, surface area and temperature affect rate, the core practicals measuring rate by gas volume and by a colour change, calculating rate from graphs, catalysts, exothermic and endothermic reactions, reaction profiles and activation energy, and bond energy calculations.

How does collision theory explain the rate of reaction?

Particles must collide with at least the activation energy and in the correct orientation to react. Anything that increases the frequency of successful collisions increases the rate. Higher concentration, higher pressure and larger surface area increase collision frequency, and higher temperature increases both the frequency and the proportion of collisions that exceed the activation energy.

How does a catalyst speed up a reaction?

A catalyst provides an alternative reaction pathway with a lower activation energy, so a greater proportion of collisions have enough energy to react and the rate increases. A catalyst is not used up in the reaction, so only a small amount is needed and it can be reused.

How do you calculate the energy change from bond energies?

Add up the bond energies of all the bonds broken in the reactants and all the bonds made in the products, then subtract the making total from the breaking total. A negative answer means the reaction is exothermic; a positive answer means it is endothermic, because breaking bonds is endothermic and making bonds is exothermic.

What is the most common mistake in Topic 7?

Common mistakes are saying particles only need to collide rather than collide with enough energy, saying a catalyst is used up or changes the overall energy change, mixing up the exothermic and endothermic temperature changes, and getting the bond-energy subtraction the wrong way round.

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Edexcel GCSE Chemistry Topic 7 Rates of reaction and energy changes: a complete overview

A deep-dive Edexcel GCSE Chemistry guide to Topic 7 Rates of reaction and energy changes. Covers collision theory and the factors affecting rate, measuring rate by gas volume and colour change, calculating rate from graphs, catalysts, exothermic and endothermic reactions and reaction profiles, and bond energy calculations.

Generated by Claude Opus 4.816 min readTopic 7Updated 2026-06-02

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What Topic 7 actually demands
Rate of reaction and collision theory
Measuring rate and catalysts
Energy changes and reaction profiles
Bond energy calculations
How Topic 7 is examined
Check your knowledge

What Topic 7 actually demands

Rates of reaction and energy changes is a Paper 2 topic that rewards consistent collision-theory reasoning, accurate handling of rate graphs, and confident bond-energy calculation. Edexcel tests the factors affecting rate, the two rate core practicals, the energetics of reactions and the reaction profile.

This guide walks through the topic in specification order, then sets out the exam patterns Edexcel repeats. Each dot point has a matching page with practice questions; this overview ties them together.

Rate of reaction and collision theory

The rate of reaction is how fast reactants are used up or products are formed. Collision theory says particles must collide with at least the activation energy and the right orientation to react. The rate increases when the frequency of successful collisions rises: higher concentration, higher pressure and larger surface area pack or expose more particles, and higher temperature makes particles move faster and gives more of them enough energy.

Measuring rate and catalysts

Two core practicals measure rate: the gas-syringe method (volume of gas over time) and the disappearing-cross method (sodium thiosulfate and acid, timing the cloudiness). The mean rate is the change divided by the time; the instantaneous rate is the gradient of a tangent to the curve. A catalyst speeds up a reaction by providing a pathway with a lower activation energy and is not used up.

Energy changes and reaction profiles

Exothermic reactions release energy and the temperature rises (combustion, neutralisation); endothermic reactions absorb energy and the temperature falls (thermal decomposition). A reaction profile shows the reactants, products, the activation energy (rise to the peak) and the overall energy change (products below reactants for exothermic, above for endothermic). The temperature-change core practical uses an insulated cup.

Bond energy calculations

Breaking bonds is endothermic and making bonds is exothermic. The overall energy change is the energy to break the reactant bonds minus the energy released making the product bonds: a negative result is exothermic, a positive result endothermic.

How Topic 7 is examined

A typical Edexcel profile for this topic:

Collision theory. Explaining the effect of each factor on rate.
Rate measurement. Describing the core practicals and calculating rate from data or graphs.
Energetics. Classifying reactions and drawing reaction profiles.
Bond energies. Calculating the overall energy change.

Check your knowledge

A mix of recall and application questions covering Topic 7. Attempt them under timed conditions, then check against the solutions.

Define the rate of reaction. (1 mark)
Explain, using collision theory, why increasing surface area increases the rate. (2 marks)
State two ways to measure the rate of a reaction that produces a gas. (2 marks)
Explain how a catalyst increases the rate. (2 marks)
State the temperature change for an exothermic and for an endothermic reaction. (2 marks)
On a reaction profile, where are the products for an exothermic reaction? (1 mark)
Calculate the energy change if breaking bonds needs $500$ kJ/mol and making releases $620$ kJ/mol, and state the type. (2 marks)
Explain why breaking bonds is endothermic. (1 mark)

Sources & how we know this

Pearson Edexcel GCSE (9-1) Chemistry (1CH0) specification — Pearson Edexcel (2016)