Question

The enthalpy of combustion of $ {{H}_{2}}, $ cyclohexene $ ({{C}_{6}}{{H}_{10}}) $ and cyclohexane $ ({{C}_{6}}{{H}_{12}}) $ are $ -241,~-3800 $ and $ -3920\text{ }kJ $ per mol respectively. Heat of hydrogenation of cyclohexene is

• A. $ -121\text{ }kJ $ per mol
• B. $ +121\text{ }kJ $ per mol
• C. $ +242\text{ }kJ $ per mol
• D. $ -242\text{ }kJ $ per mol

Answer 1

Answer: (A)

$ \Delta H=[\Delta H $ of combustion of cyclohexane $ -(\Delta H $ of combustion of cyclohexene $ +\Delta H $ of combustion of $ {{H}_{2}} $ )]
$ =-[-3920-(3800-24)]\text{ }kJ $
$ =-[3920+4041] $
$ =-[121]kJ $
$ =-121kJ $