Rate & Extent of Reactions - AQA GCSE Chemistry Revision

Topic overview

What you need to know

Rate & Extent of Reactions is a key part of GCSE Chemistry. Link particles, structure and energy changes to the observations and calculations you may be given. How fast reactants are converted into products. Rate = amount of reactant used (or product formed) ÷ time. For a reaction to occur, particles must collide with sufficient energy (≥ activation energy) and correct orientation. Increasing temperature increases the rate: particles move faster, collide more frequently, and more collisions have energy ≥ activation energy.

Exam tip

Balance equations, show units in calculations and connect macroscopic observations to particles.

Revision notes

Core ideas

Secure these ideas first. Say each definition in your own words, then connect it to the topic overview.

Rate of Reaction: How fast reactants are converted into products. Rate = amount of reactant used (or product formed) ÷ time.
Collision Theory: For a reaction to occur, particles must collide with sufficient energy (≥ activation energy) and correct orientation.
Effect of Temperature: Increasing temperature increases the rate: particles move faster, collide more frequently, and more collisions have energy ≥ activation energy.
Effect of Concentration: Higher concentration means more particles in the same volume, so collisions are more frequent, increasing the rate.

Revision notes

Apply it in the exam

The exam will rarely ask for an isolated definition. Practise selecting the right idea and using it as part of a complete explanation or method.

Effect of Surface Area: Smaller pieces (greater surface area) react faster because more particles are exposed to react.
Effect of a Catalyst: A catalyst provides an alternative reaction pathway with lower activation energy, increasing the rate.
Reversible Reaction: A reaction that can proceed in both forward and reverse directions, shown by the ⇌ symbol.
Dynamic Equilibrium: In a closed system, the rate of the forward reaction equals the rate of the reverse reaction. Concentrations remain constant.

Core knowledge

Key facts for Rate & Extent of Reactions

8 essentials

Rate of Reaction

How fast reactants are converted into products. Rate = amount of reactant used (or product formed) ÷ time.

Collision Theory

For a reaction to occur, particles must collide with sufficient energy (≥ activation energy) and correct orientation.

Effect of Temperature

Increasing temperature increases the rate: particles move faster, collide more frequently, and more collisions have energy ≥ activation energy.

Effect of Concentration

Higher concentration means more particles in the same volume, so collisions are more frequent, increasing the rate.

Effect of Surface Area

Smaller pieces (greater surface area) react faster because more particles are exposed to react.

Effect of a Catalyst

A catalyst provides an alternative reaction pathway with lower activation energy, increasing the rate.

Reversible Reaction

A reaction that can proceed in both forward and reverse directions, shown by the ⇌ symbol.

Dynamic Equilibrium

In a closed system, the rate of the forward reaction equals the rate of the reverse reaction. Concentrations remain constant.

Active recall

Close the notes and answer these

1.Without looking, explain rate of reaction and give one example or consequence.
2.Without looking, explain collision theory and give one example or consequence.
3.Without looking, explain effect of temperature and give one example or consequence.
4.Without looking, explain effect of concentration and give one example or consequence.

Content reviewed 23 July 2026 against the current linked specification.

Finished learning?

Mark the notes complete, then test what you can recall.

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