Given that bond energies of H – H and Cl – Cl are 430 kJ mol–1 and 240 kJ mol–1 respectively and f H for HCl is-90 kJ mol–1 bond enthalpy of HCl is (2007)

2 2 1 1 H Cl HCl 2 2 → 2 2 (reactants) ()products (H ) (Cl ) (HCl) (HCl) –1 (HCl) H B.E. B.E. 1[B.E. B.E. ] B.E. 90 2 1 (430 240) B.E. 90 2 1 B.E. (430 240) 90 425kJ mol 2