Chemistry 30

We can graphically represent threshold energy on a kinetic energy diagram (first introduced in Thermodynamics Section 1-3). A typical kinetic energy diagram looks like this:

This graph illustrates that some particle have a low amount of kinetic energy (yellow region), some are very energetic and fast moving and have a lot of kinetic energy (blue), while most particles have some intermediate amount of kinetic energy (purple).

Threshold energy is the minimum amount of energy needed for particles to react. For a particular reaction, the threshold energy might be as shown here:

Only particles that have at least as much energy as the required threshold energy will have enough energy to have a successful collision. Thus only particles in the green area of the graph will actually react because only they have more than the minimum amount of energy needed.

In the next graph representing a different reaction, the threshold energy is lower; more particles meet this minimum requirement, so more particles will successfully collide. This, in turn, means that this reaction will have a faster rate.