Question

The energies of activation for forward and reverse reactions for A2 + B2$\rightleftharpoons$ 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 (A2 + B2® 2AB) in the presence of catalyst will be (in kJ mol–1).

• A. 280
• B. 20
• C. 300
• D. 120

Answer 1

Answer: (B)

20

Answer 2

$\Delta H_{R}\text{ = }\text{E}_{f}\text{- }\text{E}_{b}\text{ = 180 - 200 = - 20 kJ mo}\text{l}^{\text{-1}}$

The correct answer for this question should be –20kJ mol–1. But no option given is correct. Hence we can ignore sign and select option