Q. The enthalpy of combustion of H₂, cyclohexene (C₆H₁₀) and cyclohexane (C₆H₁₂) are −241, −3800 and −3920 kJ per mol respectively. Heat of hydrogenation of cyclohexene is :
A) −121 kJ per mol
B) +121 kJ per mol
C) +484 kJ per mol
D) −484 kJ per mol
Explanation
[Solution from source] For C₆H₁₀ + H₂ → C₆H₁₂, ΔH = Σ ΔcH(reactants) − Σ ΔcH(products) = (−3800 − 241) − (−3920) = −121 kJ mol⁻¹. Reversing the subtraction gives +121 kJ mol⁻¹, but hydrogenation of an alkene is exothermic. Answer (1).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.