Question

The bond dissociation enthalpies of the H–H bond and the H–Cl bond are 435 kJ mol–1 and 431 kJ mol–1 , respectively. The ∆Hºf of HCl(
g. is –92 kJ mol–1 . What is the bond dissociation enthalpy of the Cl–Cl bond?

Answer 1

First, we write the reaction equation for the formation of HCl from hydrogen and chlorine:
H₂ + Cl₂ → 2HCl

Now, we substitute the values of the enthalpies, denoting that of the Cl-Cl bond by x:
435 + x = -92 + 2(431)
x = 335
The bond dissociation enthalpy for the Cl-Cl bond is 335 kJ/mol