Thermodynamics and Thermochemistry 2 Question 25
25. The standard enthalpy of combustion at $25^{\circ} \mathrm{C}$ of hydrogen, cyclohexene $\left(\mathrm{C}{6} \mathrm{H}{10}\right)$ and cyclohexane $\left(\mathrm{C}{6} \mathrm{H}{12}\right)$ are -241 , -3800 and $-3920 \mathrm{~kJ} / \mathrm{mol}$ respectively. Calculate the heat of hydrogenation of cyclohexene.
(1989, 2M)
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Solution:
$\Delta H=\Sigma \Delta H_{\text {comb }}^{\circ}$ (reactants) $-\Sigma \Delta H_{\text {comb }}^{\circ}$ (products)
$$ \begin{aligned} & =-3800-241-(-3920) \ & =-121 \mathrm{~kJ} / \mathrm{mol} \end{aligned} $$
