Consider the following cases of standard enthalpy of reaction \( \left(\Delta H_x^{\,\circ} \text{ in kJ mol}^{-1}\right) \)
\( \mathrm{C_2H_6(g)} + \tfrac{7}{2}\,\mathrm{O_2(g)} \rightarrow 2\mathrm{CO_2(g)} + 3\mathrm{H_2O(l)} \quad \Delta H_1^{\,\circ} = -1550 \)
\( \mathrm{C(graphite)} + \mathrm{O_2(g)} \rightarrow \mathrm{CO_2(g)} \quad \Delta H_2^{\,\circ} = -393.5 \)
\( \mathrm{H_2(g)} + \tfrac{1}{2}\,\mathrm{O_2(g)} \rightarrow \mathrm{H_2O(l)} \quad \Delta H_3^{\,\circ} = -286 \)
The magnitude of \( \Delta H_{f \, \text{C}_2\text{H}_6(g)}^{\circ} \) \( \_\_\_\_\_\_\_\_\_\_ \) \( \mathrm{kJ\,mol^{-1}} \) \( \text{(Nearest integer)} \).
