question_answer

The enthalpy of combustion of H2, cyclohexene (C6H10) and cyclohexene (C6H12) are -241, -3800 and -3920 kJ per mol respectively. Heat of hydrogenation of cyclohexene is: [AIPMT (S) 2006]

A) -121 kJ per mol

B) +121 kJ per mol

C) +242 kJ per mol

D) -242 kJ per mol

Correct Answer: A

Solution :

[a]

\[\Delta H=\] [\[\Delta H\]of combustion of cyclohexane

- (\[\Delta H\] of combustion of cyclohexene

+\[\Delta H\]of combustion of H2)]

\[=-[-3920-(3800-24)]\,kJ\]

\[=-[3920+4041]\,kJ\]

= -[121] kJ

= -121 kJ