A reaction is endothermic with $\mathrm{\Delta H}=100\mathrm{kJ}/\mathrm{mol}$. If the activation enthalpy of the forward reaction is $140. \mathrm{kJ}/\mathrm{mol}$. what is the activation enthalpy of the reverse reaction?

The activation enthalpy of the reverse reaction is found as,

= activation enthalpy of the forward reaction - change in the enthalpy

The activation enthalpy of the reverse reaction is found as,

= 140-100

=40 kj/mol