Question
From the following data, calculate the enthalpy change (in kJ/mol) for the combustion of cyclopropane(g) at 298 K. The enthalpy of formation of CO2(g), H2O(l) and propene(g) are −394, −286 and 20 kJ/mol, respectively. The enthalpy of isomerization of cyclopropane(g) to propene(g) is −33 kJ/mol.
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Solution
$\Delta(g) + \frac{9}{2}O_{2}(g) \rightarrow 3CO_{2}(g) + 3H_{2}O(l)$
$\Delta_{C}H_{\text{cyclopropane}} = \left\lbrack 3 \times \Delta_{f}H_{CO_{2}(g)} + 3 \times \Delta_{f}H_{H_{2}O(l)} \right\rbrack - \left\lbrack \Delta_{f}H_{\text{cyclopropane}} + \frac{9}{2} \times \Delta_{f}H_{O_{2}(g)} \right\rbrack $$$= \left\lbrack 3 \times ( - 394) + 3 \times ( - 286) \right\rbrack - \left\lbrack \left\{ 33 + 20 \right\} + \frac{9}{2} \times 0 \right\rbrack = - 2093\text{ kJ/mol}$$
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