1.5 Kinetics (AS)
The study of kinetics enables chemists to determine how a change in conditions affects the speed of a chemical reaction. Whilst the reactivity of chemicals is a significant factor in how fast chemical reactions proceed, there are variables that can be manipulated in order to speed them up or slow them down.
- 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.
- Maxwell-Boltzmann distribution - Maxwell–Boltzmann distribution of molecular energies in gases. Students should be able to draw and interpret distribution curves for different temperatures.
- 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
- 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
- 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.