The energies of activation for forward and reverse reactions for $A_2 + B_2 \leftrightharpoons 2AB$ are $180\; kJ\;mol^{-1}$ and $200 \; kJ \;mol^{-1}$ respectively. The presence of a catalyst lowers the activation energy of both (forward and reverse) reactions by $100\; kJ\; mol^{-1}$. The enthalpy change of the reaction ($A_2 + B_2 \to 2AB$) in the presence of catalyst will be (in $kJ\;mol^{-1}$) :
