Question

The enthalpy of combustion of `H_(2)` , cyclohexene `(C_(6)H_(10))` and cyclohexane `(C_(6)H_(12))` are `-241` , `-3800` and `-3920KJ` per mol respectively. Heat of hydrogenation of cyclohexene is
A. `-121kJ//mol`
B. `+121kJ//mol`
C. `-242kJ//mol`
D. `+242kJ//mol`

Answer 1

Correct Answer - A
`H_(2)(g)+(1)/(2)O_(2)(g)toH_(2)O(l)(DeltaH=-241kJ)` . . .(i)
`C_(6)H_(10)+(17)/(2)O_(2)(g)to6CO_(2)(g)+5H_(2)O(l)" "(DeltaH=-3800kJ)`
`C_(6)H_(12)+9O_(2)(g)to6CO_(2)+6H_(2)O(l)" "(DeltaH=-3920kJ)` . . .(iii)
eq. (i) eq. (ii)-eq.(iii) gives
for `DeltaH=-241-3800-(-3920)=-121kJ`
for `C_(6)H_(10)+H_(2)toC_(6)H_(12)`.