Dissociation enthalpies of methane, ethane and ethylene are respectively 400, 680 and 540 k cal `mol^(-1)` . Calculate `sigma C-H, sigma C-C and pi C-C `bond energies.

Explanation

Methane has four `sigma `C-H bonds.
`sigma ` C-H bond energy `=(400) /(4) `=100 kcal `mol^(-1)`
Ethane has six `sigma ` C-H bonds and one `sigma ` C-C bond. `sigma ` C-C bond energy = 680 - (6`xx`100) = 80 k cal `mol^(-1)`
Ethylene has four `sigma ` C-H bonds, one `sigma ` C-C bond and one `pi` C-C bond.
`pi ` C-C bond energy = 540 - [(4`xx`100) + 80]
= 60 kcal` mol^(-1)`