We know that the activation energy of chemical reaction is given by formula =‌
k2
k1
=‌
Ea
2.303R
[‌
T2−T1
T1T2
], where k1 is the rate constant at temperature T1 and k2 is the rate constant at temperature T2 and Ea is the activation energy. Therefore activation energy of chemical reaction is determined by evaluating rate constant at two different temperatures.