Question

Standard enthalpy of combustion at 25°C of hydrogen, cyclohexene (C₆H₁₀) and cyclohexane (C₆H₁₂) are – 240, – 3800 and – 3920 kJ/mol respectively. The heat of hydrogenation of cyclohexene is ______.

विकल्प

• – 120 kJ

• – 121 kJ

• + 120 kJ

• + 121 kJ

Answer 1

Standard enthalpy of combustion at 25°C of hydrogen, cyclohexene (C₆H₁₀) and cyclohexane (C₆H₁₂) are – 240, – 3800 and – 3920 kJ/mol respectively. The heat of hydrogenation of cyclohexene is – 120 kJ.

Explanation:

Given,

\[\ce{H2_{(g)} + 1/2 ->  H2O_{(l)}; ΔH = - 240 J}\]  ......(i)

\[\ce{C6H10_{(l)} + 17/2 O2_{(g)} -> 6CO2_{(g)} + 5H2O_{(l)}; ΔH = - 3800 kJ}\]  ......(ii)

\[\ce{C6H12_{(l)} + 9O2_{(g)} -> 6CO2_{(g)} + 6H2O_{(l)}; ΔH = - 3920 kJ}\]  ......(iii)

The necessary equation is

\[\ce{C6H10_{(l)} + H2_{(g)} -> C6H12_{(l)} ; ΔH = ?}\]

It could be accomplished by the action.

(i) + (ii) – (iii)

ΔH = (– 240) + (– 3800) – (– 3920)

= – 4040 + 3920

= – 120 kJ