Question

The standard enthalpy of formation $\left(\Delta_{f}H^{\circ}\right)$ 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 hydrogen molecule, $H_2$
• B. The dissociation energy of $H_2$ and enthalpy of sublimation of carbon
• C. Latent heat of vaporisation of methane
• D. The first four ionisation energies of carbon and electron gain enthalpy of hydrogen

Answer 1

Answer: (B)

$C + 2H_2\to CH_4$
$\Delta_{f}H^{\circ}=\left[e_{C\left(s\to g\right)}+2\times e_{H-H}-4\times e_{C-H}\right]$