AQA GCSE Chemistry (Triple) - Paper 2: The Rate and Extent of Chemical Change

Rate of a chemical reaction

The speed at which reactants are converted into products.

Collision theory

Reactions occur when particles collide with enough energy (activation energy) to start.

Activation energy

The minimum amount of energy that reacting particles must have to cause a reaction.

Factors that affect the rate of reaction

Temperature, concentration (or pressure for gases), surface area, and use of a catalyst.

Effect of increasing temperature on reaction rate

Particles have more kinetic energy → collide more frequently and with more energy.

Effect of increasing concentration on reaction rate

More particles in a given volume → more frequent collisions → higher rate.

Effect of increasing pressure on gas reaction rate

Particles are closer together → collide more frequently → higher rate.

Effect of increasing surface area on reaction rate

More particles are exposed to collisions → faster rate (especially for solids).

Role of a catalyst

A catalyst speeds up a reaction by providing an alternative reaction pathway with lower activation energy.

Do catalysts get used up in reactions?

No — they are not used up or chemically changed at the end of the reaction.

Importance of catalysts in industry

They reduce energy costs, speed up reactions, and can allow reactions to occur at lower temperatures.

Reversible reaction

A reaction that can go both forwards (reactants → products) and backwards (products → reactants).

Closed system in a reversible reaction

The forward and reverse reactions continue, but the concentrations of reactants and products remain constant.

Dynamic equilibrium

The state in a closed system where the rate of the forward and reverse reactions are equal.

When is equilibrium reached?

When the forward and backward reactions occur at the same rate in a closed system.

Le Chatelier’s Principle