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) rarr H_(2)O, Delta H = -241kJ`
(ii) `C_(6)H_(10)=(17)/(2) O_(2) rarr 6CO_(2) + 5H_(2)O, Delta H = -3800kJ`
(iii) `C_(6)H_(12) + 9O_(2) rarr 6CO_(2) + 6H_(2)O, Delta H= -3920kJ`
`C_(6)H_(10) + H_(2) rarr C_(6)H_(12)`
Eq (i) + Eq (ii)- Eq (iii)
`Delta H= -241 - 3800- (-3920)`
`=-4041 + 3920 = -121kJ`