Question

How do you calculate the activation energy of a reaction?

Answer 1

You can use the Arrhenius equation in various ways, it depends on what information you are given to find the Ea.

The Arrhenius equation is:
\[k = Ae^{Ea/RT}\]
A more useful version for you would be a derived form of the above equation:
\[\ln(k)=(-E _{a}/RT)+\ln(A)\]
Assuming that you are given enough information you can play around with those equations to solve for Ea, your Activation Energy.