Calculate the C-C bond enthalpy from the following data :
`2C("graphite") + 3H_(2)(g), to C_(2)H_(6)(g) Delta_(r)H^(@) = -84.67mkJ`
`C("graphite"), to C(g) Delta_(r)H^(@) = 716.7kJ`
`H_(2)(g), to 2H(g) Delta_(r)H^(@) = 435.9 kJ`
Assume 416 kJ as the C-H bond enthalpy.

Answer

`329.77kJ`

Explanation

Let us calculate `DeltaH` for the reaction, `C_(2)H_(6)(g),i.e., H - underset(H) underset(|) overset(H) overset(|) (C)-underset(H) underset(|) overset(H) overset(|) (C) -H(g) rarr 2C(g) +6H(g)`
` 2 xx `Eqn. (ii) `+3 xx ` Eqn. (iii) -Eqn. (i) gives `Delta _(r)H= 2825.77 kJ`
If x is the bond energy of C-C bond,then `x+ 6 B.E. ( C-H)= 2825.77`
`x +6 ( 416) = 2825.77` or `x=329.77kJ`