The bond energies of `C=C` and `C-C` at `298 K` are `590` and `331 kJ mol^(-1)`, respectively. The enthalpy of polymerisation per mole of ethaylene is

Options

A. `-70 Kj`
B. `-72 Kj`
C. 72 Kj
D. `-68` Kj

Answer

B

Explanation

The polymenzation of ethane may be represented as `nCH_(2)=CH_(2) to {-CH_(2) - CH_(2)-}n`.
One mole of C=C bond is decomposed and two moles of C-C bonds are formed per mole of ethylene.
`DeltaH = 590 -2 xx 331 = -72` KJ per mole.