The enthalpy of combustion of `H_(2)`, cyclohexene (`C_(6)H_(10)`) and cyclohexane (`C_(6)H_(12)`) are `-241, – 3800` and `- 3920 kJ "mol"^(-1)` respectively. The heat of hydrogenation of cyclohexene is:

Options

A. `121 "kJ mol"^(-1)`
B. `-121 "kJ mol"^(-1)`
C. `+242 "kJ mol"^(-1)`
D. `-242 "kJ mol"^(-1)`

Answer

B

Explanation

Given:
(i) `H_(2) + 1/2 O_(2) to H_(2)O, DeltaH - 241 "kJ mol"^(-1)`
(ii) `C_(6)H_(10) + 17/2 O_(2) to 6 CO_(2) = 5H_(2)O, DeltaH = -3800 "kJ mol"^(-1)`
(iii) `C_(6)H_(12) + 9 O_(2) to 6CO_(2) + 6H_(2)O, DeltaH = -3920 "kJ mol"^(-1)`
The reaction, `C_(6)H_(10) + H_(2) to C_(6)H_(12)` = Equation (i)+ Equation (ii)- Equation (iii) Thus, `DeltaH = -241 - 3800 - (-3920) = -121 "kJ mol"^(-1)`