The energies of activation for forward and reverse reactions for $ {A2 + B2<=>2AB}$ are $180\, kJ \,mol^{-1}$ and $200\, kJ\, mol^{-1}$ respectively. The presence of catalyst lowers the activation energy of both (forward and reverse) reactions by $100\, kJ\, mol^{-1}$. The enthalpy change of the reaction ($ {A2 + B2->2AB}$) in the presence of catalyst will be (in $kJ\, mol^{-1}$)