Question

Bond dissociation enthalpy of H₂, Cl₂ and HCl are 434, 242 and 431 kJ mol ^-1 respectively. Enthalpy of formation of HCl is

(a) -93 kJ mol^-1

(b) 245 kJ mol^-1

(c) 93 kJ mol^-1 

(d) -245 kJ mol^-1

Answer 1

The correct option is: (a) -93 kJ mol^-1

Explanation:

Heat of formation is the amount of heat absorbed or evolved when one mole of substance is directly obtained from its constituent element.

Hence, enthalpy of formation of HCI = -186/2 kJ

= -93 kJ mol^-1