Why temperature affects rate

Temperature affects the rate of a reaction in two ways.

First, we already know that temperature is a measure of how fast particles are moving. As the temperature increases, the particles move faster. This means that they will collide more often. More collisions means the rate of the reaction will increase.

Secondly, in addition, if the particles are moving faster then the collisions that do occur will have more energy. As a result, more of them will have “enough” energy to react, also increasing the rate.

One way to make sense of this is to look at the Boltzmann diagram. In this diagram, we see how the distribution of molecules changes with a change in temperature.

When temperature is increased, the average kinetic energy increases and the spread of kinetic energies also increases.

The amount of energy needed for a reaction (the “enough” from collision theory) can be shown on the graph with a vertical line.

At a low temperature, only a small portion of the molecules have enough energy to react. At a higher temperature, more of the molecules have “enough”. This means that more of the collisions that occur at that higher temperature will result in a reaction.