GCSE Chemistry · AQA 8462 · Topic 4.6
The rate and extent of chemical change
Key points
- The rate of reaction is how quickly reactants are used up or products are formed: mean rate = quantity ÷ time.
- Rate increases with higher temperature, concentration or pressure, larger surface area (smaller pieces) and a catalyst.
- Collision theory: particles must collide with at least the activation energy. More frequent or more energetic collisions mean a faster rate.
- A catalyst speeds up a reaction by providing a pathway with lower activation energy and is not used up.
- Reversible reactions can go both ways (). If one direction is exothermic, the other is endothermic by the same amount.
- In a closed system a reversible reaction reaches dynamic equilibrium, where forward and reverse rates are equal.
- (Higher) Le Chatelier's principle predicts how changing conditions shifts the position of equilibrium.
Topic notesPremium
Two questions matter for any useful reaction: how fast does it go, and how far does it go? This topic covers both: the rate of reaction and the extent of reactions that can go both ways.
Unlock the full notes with Premium
Premium includes full topic notes, the paper generator, self-quizzes and progress tracking.
Sub-topics
Practise this topicPremium
Premium members can generate an exam-style paper with a mark scheme, or take a quick quiz, on The rate and extent of chemical change.