The energies of activation for forward and reverse reactions for A2+B2⇋2AB are 180kJmol−1 and 200kJmol−1 respectively. The presence of a catalyst lowers the activation energy of both (forward and reverse) reactions by 100kJmol−1. The enthalpy change of the reaction (A2+B2→2AB) in the presence of catalyst will be (in kJmol−1) :