Question

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

(a) 20 

(b) 300

(c) 120 

(d) 280.

Answer 1

(a) : ΔH_R = E_f - E_b = 180 - 200 = - 20 kJ mol^–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 (a).