Kinetics Objectives 6.2.5 to 6.2.7

6.2.5 Sketch and explain qualitatively the Maxwell-Boltzmann energy distribution curve for a fixed amount of gas at different temperature and its consequences for changes in reaction rate

The Maxwell-Boltzmann Distribution Curve

The fact that particles in a gas at a particular temperature show a range of values of kinetic energy is express by the Maxwell-Boltzmann distribution curve.

This shows the number of particles that have a particular value of kinetic energy (or the probability of that value occurring) plotted against the values for kinetic energy. The area under the curve represents the total number of particles in the sample.

6.2.6 Describe the effect of a catalyst on a chemical reaction

A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing permanent change.

Most catalysts work by providing an alternate route for the reaction, which has lower activation energy.

This means that without increasing the temperature, a larger number of particles has the value of kinetic energy greater than the activation energy and so will be able to undergo successful collisions.

6.2.7 Sketch and explain Maxwell-Boltzmann curves for reactions with and without catalyst

Without a catalyst there are a smaller number of particles that has the value of kinetic energy greater than the activation energy. This means that a fewer number of particles will able to undergo successful collisions and the rate of reaction will be slower.

With a catalyst the activation energy is lowered and there is therefore a greater number of particles that has the value of kinetic energy than the activation energy. This means that a greater number of particles will be able to undergo successful collisions and the rate of reaction will be faster.


This can be seen in the reaction of aluminium and iodine catalyzed using water, shown in this video: