Question

The dissociation energy of methane is $360kcalmo{l}^{-1}$. The average bond energy of $C--H$ bond in $kcalmo{l}^{-1}$ is ______.

Answer 1

The bond dissociation enthalpy is the energy needed to break one mole of the bond to give separated atoms - everything being in the gas state.

In the methane case, 360 kcal/mol energy is needed to break a mole of methane gas into gaseous carbon and hydrogen atoms and it involves breaking 4 moles of C-H bonds.

The average bond energy is, therefore, $\frac{+360}{4}$ kcal/mol, which is $90$ kcal per mole of bonds.