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.

Answer

121 kj/mole

Explanation

The required reaction is
`underset("Cyclohexene")(C_(6)H_(10)) + H_(2) rarr underset("Cyclohexene")(C_(6)H_(12)), Delta H_(1) = ?`....(i)
Given `H_(2) + (1)/(2) O_(2) rarr H_(2)O, Delta H_(2) = - 241 kJ//"mole"`.... (ii)
`C_(6)H_(10) + (17)/(2) O_(2) rarr 6 CO_(2) + 5H_(2)O, DeltaH_(3) = -3800 kJ//"mole"`....(iii)
`C_(6) H_(12) + 9O_(2) rarr 6 CO_(2) + 6 H_(2)O, Delta H_(4) = -3920`kJ/mole.....(iv)
add (ii) and (iii)
`C_(6)H_(10) + H_(2) 9 O_(2) rarr 6 CO_(2) + 6H_(2)O DeltaH_(5) = 404` kJ/mole
Substract (iv) from (v) `C_(6)H_(10) + H_(2) rarr C_(6) O_(12) Delta H = 121` kJ/mole