# Given, standard enthalpy of formation $(\Delta _f H^\circ)$ at 298 k for methane is -74.8 kJ/mol. What other information is required to determine the average energy for C-H bond formation would be

(a) The first four ionisation of carbon and electron gain enthalpy of hydrogen
(b) The dissociation energy of hydrogen molecule $H_2$
(c) The dissociation energy of $H_2$ and enthalpy of sublimation of carbon
(d) latent heat of vaporisation of methane

Answer: The dissociation energy of $H_2$ and enthalpy of sublimation of carbon
Given $C(graphite) + 2H_2(g) \rightarrow CH_4(g)$ ; $\Delta H = -71.8$ kJ/mol
Aim $\frac{1}{4}[CH_4(g)\rightarrow C(g) + 4H(g)]$ ; $\Delta H =?$
Hence, to calculate average $\Delta H$ for C-H bond, we require dissociation energy of $H_2$ and enthalpy of sublimation of carbon.