The energies of activation for forward and reverse reactions for A₂+B₂ 2 A B 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 ( A ₂+ B ₂ 2 AB ) in the presence of catalyst will be (in kJ ~mol ⁻¹ )