Concept of activation energy:
The minimum extra amount of energy absorbed by the reactant molecules so that their energy becomes equal to threshold value is called activation energy.
In other words, activation energy is the difference between the threshold energy and the average energy of the reactant molecules i.e.
Activation energy = Threshold energy – Average energy of the reactant
At room temperature, most of the reactant molecules have energy less than the threshold value. However, if energy is supplied in the form of heat, light etc, the reactant molecules absorb this energy becomes equal to or greater than threshold value. Hence, they start change into products.
Evidently, less is the activation energy, faster is the reaction or greater is the activation energy, slower is the reaction. For example:
Consider the following reaction:
2NO + O2 —————-> 2NO2 is fast reaction because of low activation energy whereas the reaction below:
2CO + O2 ——————> 2CO2 appears to be similar, is slow reaction because of high activation energy.
