What does Edexcel Combined Science CC7 cover?

CC7 covers the factors that affect the rate of reaction (temperature, concentration, surface area and catalysts), collision theory and activation energy, how to measure and calculate rate, and exothermic and endothermic reactions with reaction profile diagrams. It is studied alongside the group trends of the periodic table from CC6.

What does collision theory say?

Collision theory states that particles must collide with at least a minimum energy, the activation energy, for a reaction to happen. The rate depends on how frequently particles collide and what proportion of collisions have the activation energy. Anything that increases the frequency or energy of successful collisions speeds up the reaction.

How does a catalyst work?

A catalyst speeds up a reaction by providing a different reaction pathway with a lower activation energy, so a greater proportion of collisions are successful. A catalyst is not used up in the reaction, so a small amount can be reused many times. Enzymes are biological catalysts.

What is the difference between exothermic and endothermic reactions?

An exothermic reaction transfers energy to the surroundings, so the temperature rises; examples include combustion and neutralisation. An endothermic reaction takes in energy from the surroundings, so the temperature falls. On a reaction profile, exothermic reactions have products below the reactants and endothermic reactions have products above.

How does reactivity change down groups 1 and 7?

In group 1 (the alkali metals), reactivity increases down the group because the outer electron is further from the nucleus and lost more easily. In group 7 (the halogens), reactivity decreases down the group because atoms gain an electron less easily. Group 0 (noble gases) are unreactive because they have full outer shells.

EnglandCombined Science

Edexcel GCSE Combined Science CC7 Rates of reaction and energy changes: a complete overview of rate, collision theory, energy changes and the groups

A deep-dive Edexcel GCSE Combined Science guide to Topic 7 (CC7) Rates of reaction and energy changes, with the group trends from Topic 6 (CC6). Covers the factors affecting rate, collision theory, catalysts, measuring rate, exothermic and endothermic reactions, reaction profiles and activation energy, and the reactivity trends of groups 1, 7 and 0.

Generated by Claude Opus 4.814 min readCC7Updated 2026-06-02

Reviewed by: AI editorial process; not yet individually human-reviewed

Jump to a section

What CC7 actually demands
Rate and collision theory
Energy changes
Group trends
How CC7 is examined
Check your knowledge

What CC7 actually demands

Rates of reaction and energy changes is examined on Chemistry Paper 2, alongside the group trends. The examiners reward collision-theory explanations that mention the activation energy, rate calculations with units, correct reaction profiles, and the contrasting reactivity trends of groups 1 and 7.

This guide walks through the topic and ties together the matching dot-point pages, each with its own practice questions.

Rate and collision theory

The rate increases with higher temperature, concentration (or pressure), surface area and a catalyst. Collision theory explains this: a reaction needs collisions with at least the activation energy, and rate depends on the frequency and energy of collisions. A catalyst lowers the activation energy and is not used up. Rate is measured by gas volume, mass loss, or time to turn cloudy, and calculated as amount per unit time.

Energy changes

Exothermic reactions give out energy (temperature rises); endothermic reactions take in energy (temperature falls). On a reaction profile, exothermic reactions have products below the reactants, endothermic above, with the activation energy as the hump.

Group trends

Group 1 (alkali metals): reactivity increases down the group.
Group 7 (halogens): reactivity decreases down the group; a more reactive halogen displaces a less reactive one.
Group 0 (noble gases): unreactive because of full outer shells.

How CC7 is examined

Collision theory. Explaining each rate factor, always including the activation-energy point for temperature.
Calculations. Finding the mean rate from data, with units.
Energy. Classifying reactions and drawing reaction profiles.
Groups. Describing and explaining the reactivity trends of groups 1 and 7.

Check your knowledge

A mix of recall and calculation questions covering CC7. Attempt them under timed conditions, then check against the solutions.

State four factors that affect the rate of a reaction. (2 marks)
What is the activation energy? (1 mark)
Explain how a catalyst speeds up a reaction. (2 marks)
A reaction makes 90 cm3 of gas in 30 s. Calculate the mean rate. (2 marks)
Is a reaction that makes the temperature rise exothermic or endothermic? (1 mark)
On a reaction profile, where are the products of an exothermic reaction? (1 mark)
Describe the reactivity trend down group 1. (1 mark)
Why are the noble gases unreactive? (1 mark)

Sources & how we know this

Edexcel GCSE (9-1) Combined Science (1SC0) specification — Pearson (2016)