Question

The enthalpy of combustion at `25^(@)C` of `H_(2)(g)`, cyclohexane and cyclohexene are -241, 3920 and `-3717 kJ "mole"^(-1)` respectively. The heat of hydrogenation of cyclohexene is ( Kcal/mole) approximate integer:

Answer 1

Correct Answer - 9 Kcal/mole
`H_(2)+(1)/(2)O_(2) rarrH_(2)O " "DeltaH= -241`.......(1)
`C_(6)H_(10)+(17)/(2)O_(2)rarr6CO_(2)+6H_(2)O" "Delta H= -3717`.....(2)
`C_(6)H_(12)+9O_(2)rarr6CO_(2)+6H_(2)O" "Delta H= -3920`......(3)
eq.(1)+eq.(2)-eq.(3)
`C_(6)H_(10)+H_(2)rarrC_(6)H_(12)`
`Delta H= -241-3717-(-3920)`
`Delta H= -38 kJ//"mole"`
`Delta H ~= -9 kcal//"mole"`