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

Options

A. `-121 kJ// mol`
B. `+ 121 kJ// mol`
C. `-242 kJ // mol`
D. `+242 kJ // mol. `

Answer

A

Explanation

Given : `(I) H_2 +1/2 O_2 rarr H_O, Delta H = -241 kJ `
(ii) `C_6H_(10)+ 17/2 O_2 rarr 6 CO_2 + 5H_2O, Delta H=- 3800 kJ `
(iii) `C_6 H_(12)+H_2 rarr C_6H_(12)`
Eqn (i) + Eqn (ii) -Eqn(ii) -Eqn(iii)
`Delta H= -241-3800 -(- 3900) =- 121 kJ. `