The dissociation energy of CH₄ is 400K.Cal mol^-1 and that of ethane is 670K.Cal mol^-1 . The C-C bond energy is
 

$$\begin{gathered} {\mathrm{CH}}_4\to \mathrm{C}+4\mathrm{H}, ∆\mathrm{H}=400 \mathrm{kcals}; \\ \mathrm{B}.\mathrm{E} \mathrm{of} \mathrm{C}-\mathrm{H} \mathrm{bond}=\frac{400}{4}=100 \mathrm{kcals}; \\ \mathrm{Ethane} \mathrm{is} {\mathrm{H}}_3\mathrm{C}-{\mathrm{CH}}_3; \\ \mathrm{It} \mathrm{contains} 6 \mathrm{C}-\mathrm{H} \mathrm{bonds} \mathrm{and} 1 \mathrm{C}-\mathrm{C} \mathrm{bond}; \\ \mathrm{Thus}, \\ 6\left(100 \mathrm{kcals}\right)+ \mathrm{one} \mathrm{C}-\mathrm{C} \mathrm{bond} \mathrm{energy}=670 \mathrm{kcals}; \\ \mathrm{C}-\mathrm{C} \mathrm{B}.\mathrm{E}=70 \mathrm{kcals}/\mathrm{mole} ; \end{gathered}$$