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 think about this is to look at the Boltzmann diagram.

 

 

 

 

 

 

 

When temperature increases, the average speed increases and the spread of speeds increases.

 

 

 

 

 

 

 

 

 

The amount of enegy needed for a reaction (the “enough” from collision theory) can be shown on the graph. At a low temperature, only a small portion of the molecules have enough energy to react.

Diagram Boltzmann_3

At a higher temperature, more of the molecules have “enough”.

Diagram Boltzmann_4

This means that more of the collisions that occur will result in a reaction

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