Question

The standard enthalpy of formation $\left(\Delta H^{\circ}_{f}\right)$ at 298 K for methane, $CH_{4} \left(g\right)$, 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)

Carbon is found in solid state. The state ol substance affects the enthalpy change.
$C\left(S\right) \to C\left(g\right)$ Sublimation
and $H_{2} \left(g\right) \rightarrow 2H \left(g\right)$ dissociation
are required for C—H bond