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

$\begin {array} {1 1} (A)\;\text{the dissociation energy of $H_2$ and enthalpy of sublimation of carbon.} \\ (B)\;\text{latent heat of vaporization of methane} \\ (C)\;\text{the first four ionization energies of carbon and electron gain enthalpy of hydrogen.}\\ (D)\;\text{the dissociation energy of hydrogen molecule} \end {array}$

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Carbon is found in solid state. The state of substance affects the enthalpy change.
$C(s) \rightarrow C(g)$ sublimation and
$H_2(g) \rightarrow 2H(g)$ dissociation
are required for $C-H$ bond
Ans : (A)
answered Mar 18, 2014 by thanvigandhi_1

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