Question

The standard enthalpy of formation $\left(\Delta H^{\circ}_{f}\right)$ at 298 K for methane, $CH_4(g)$, is $- 74.8 \,kJ\, mol^{-1}$. The additional information required to determine the average energy for C�H bond formation would be:

• A. the dissociation energy of $H_2$ and enthalpy of sublimation of carbon
• B. latent heat of vaporization of methane
• C. the first four ionization energies of carbon and electron gain enthalpy of hydrogen
• D. the dissociation energy of hydrogen molecule, $H_2$.

Answer 1

Answer: (A)

the dissociation energy of $H_2$ and enthalpy of sublimation of carbon

Answer 2

Carbon is found in solid state. The state ol substance affects the enthalpy change. $C \,(s) \to C\, (g)$ Sublimation and $H_2(g) \to 2H(g)$ dissociation are required for C�H bond