Catalysts (kinetics, AS)

Definition A catalyst is a substance that increases the rate of a chemical reaction without being changed in chemical composition or amount. Catalysts work by providing an alternative reaction route of lower activation energy. Students should be able to use a Maxwell–Boltzmann distribution to help explain how a catalyst increases the rate of a reaction involving a gas.

Effect of concentration and pressure

The qualitative effect of changes in concentration on collision frequency. The qualitative effect of a change in the pressure of a gas on collision frequency. Students should be able to explain how a change in concentration or a change in pressure influences the rate of a reaction. Assessment and practical opportunities Students could investigate the effect of changing the concentration of acid on the rate

Effect of temperature on reaction rate

Meaning of the term rate of reaction. The qualitative effect of temperature changes on the rate of reaction. Students should be able to: • use the Maxwell–Boltzmann distribution to explain why a small temperature increase can lead to a large increase in rate. Assessment and practical opportunities  Students could investigate the effect of temperature on the rate of reaction of sodium thiosulfate and hydrochloric acid by an

Maxwell-Boltzmann distribution

Maxwell–Boltzmann distribution of molecular energies in gases. Students should be able to draw and interpret distribution curves for different temperatures.

Collision theory

Reactions can only occur when collisions take place between particles having sufficient energy. This energy is called the activation energy. Students should be able to: • define the term activation energy • explain why most collisions do not lead to a reaction.