Question

The standard enthalpy of formation (ΔH_f°) at 298K for methane, CH_4(g) is –74.8kJ mol^–1. The additional information required to determine the average energy for C – H bond formation would be
(a) the dissociation energy of H₂ and enthalpy of sublimation of carbon
(b) latent heat of vaporisation of methane
(c) the first four ionisation energies of carbon and electron gain enthalpy of hydrogen
(d) the dissociation energy of hydrogen molecule, H₂ .

Answer 1

(a) : C + 2H₂ → CH₄ ; ΔH° = –74.8kJ mol^–1
In order to calculate average energy for C – H bond formation we should know the following data.
C_(graphite) → C_(g) ; ΔH°_f = enthalpy of sublimation of carbon
H_2(g) → 2H_(g) ; ΔH° = bond dissociation energy of H₂