Question

The bond dissociation energy of gaseous H₂, Cl₂ and HCl are 104, 58 and 103 kcal mol^–1 respectively. The enthalpy of formation for HCl gas will be

(1) – 44.0 kcal 

(2) – 22.0 kcal

(3) 22.0 kcal 

(4) 44.0 kcal

Answer 1

Correct Answer is: (2) – 22.0 kcal

Divide equation (1) and (2) by 2, and then add

Subtracting equation (3) from equation (4)

∴ Enthalpy of formation of HCl gas = – 22.0 kcal