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.

Options

A. `- 121` KJ/mole
B. `+ 121` KJ/mole
C. `- 242` KJ/mole
D. `+ 242` KJ/mole

Answer

A

Explanation

(i) `H_(2)+(1)/(2)O_(2)rarrH_(2)O, DeltaH=-241 kJ`
(ii) `C_(6)H_(10)+(17)/(2)O_(2)rarr6CO_(2)+5H_(2)O, DeltaH=-3800 kJ`
(iii) `C_(6)H_(12)+9O_(2)rarr6CO_(2)+6H_(2)O, DeltaH=-3920 kJ`
`C_(6)H_(10)+H_(2)rarrC_(6)H_(12)`
Eq.(i) + Eq. (ii) - Eq. (iii)
`DeltaH=-241-3800-(-3920)`
`=-4041+3920=-121 kJ`.