The standard enthalpy of formation `(Delta_(f)H^(@))` at `298K ` for methane `(CH_(4(g)))` is `-74.8kJ mol^(-1)`. The additional information required to determine the average energy for `C-H` bond formation would be `:`

Options

A. The dissociation energy of the hydrogen molecule `H_(2)`
B. The first four ionisation energies of carbon
C. The dissociation energy of `H_(2)` and enthalpy and sublimation of carbon (graphite)
D. The first four ionisation energies of carbon and electron affinity of hydrogen.

Answer

A

Explanation

To calculate average enthalpy of C=H bond in methane following informations are needed.
(i) dissociation enegy of `H_(2)` i.e.
`1/2H_(2)(g)toH(g),DeltaH=x` (suppose)
(ii) Sublimation energy of C(graphite) to C(g)
C(graphite)`toC(g),DeltaH=y` (suppose)
Given
C(graphite)`+2H_(2)(g)toCH_(4)(g),DeltaH=75kJ"mol"^(-1)`