The standard ethelpy of combustion at `25^(@)C` of hydrogen, cyclohexene `(C_(6)H_(10))`, and cyclohexane `(C_(6)H_(12))` are `-241,-3800`, and `-3920 kJ mol^(-1)` repectively. Calculate the heat of hydrogenation of cyclohexane.

Explanation

Given that,
(i) `H_(2)(g)+(1)/(2)O_(2)(g) to H_(2)O(l),DeltaH=-241 "kJ"`
(ii) `C_(6)H_(10)(g)+8(1)/(2)O_(2)(g) to 6CO_(2)(g)+5H_(2)O(l),DeltaH=-3800 "kJ"`
(iii) `C_(6)H_(12)(g)+9O_(2)(g) to 6CO_(2)(g)+6H_(2)O(l),DeltaH=-3920"kJ"`
We have to calculate `DeltaH` of the reaction,
`C_(6)H_(10)(g)+H_(2)(g) to C_(6)H_(12)(g),DeltaH=?`
Applying the inspection method, i.e.,
Eqn.(i)+Eqn.(ii)-Eqn.(iii), we get,
`H_(2)(g)+(1)/(2)O_(2)(g)+C_(6)H_(10)(g)+8(1)/(2)O_(2)(g)-C_(6)H_(12)(g)-9O_(2)(g) to H_(2)O(l)+6CO_(2)(g)+5H_(2)O(l)-6CO_(2)(g)-6H_(2)O(l),DeltaH=-241+(-3800)-(-3920)`
or `C_(6)H_(10)(g)+H_(2)(g) to C_(6)H_(12)(g),DeltaH=-121 "kJ"`