Chemistry - Thermochemistry Question with Solution | TestHub

Consider the following cases of standard enthalpy of reaction $(\Delta {\mathrm{H}}_{\mathrm{r}}^{\circ }$ in $\mathrm{kJ}\mathrm{mol}{}^{-1})$ $\begin{array}{rl}& {\mathrm{C}}_2{\mathrm{H}}_6(\mathrm{g})+\frac{7}{2}{\mathrm{O}}_2(\mathrm{g})\to 2{\mathrm{CO}}_2(\mathrm{g})+3{\mathrm{H}}_2\mathrm{O}(\mathrm{l})\Delta {\mathrm{H}}_1^{\circ }=-1550\\ & \mathrm{C}\text{ (graphite) }+{\mathrm{O}}_2(\mathrm{g})\to {\mathrm{CO}}_2(\mathrm{g})\Delta {\mathrm{H}}_2^{\circ }=-393.5\\ & {\mathrm{H}}_2(\mathrm{g})+\frac{1}{2}{\mathrm{O}}_2(\mathrm{g})\to {\mathrm{H}}_2\mathrm{O}(\mathrm{l})\Delta {\mathrm{H}}_3^{\circ }=-286\end{array}$ The magnitude of $\Delta {\mathrm{H}}_{f{\mathrm{C}}_2{\mathrm{H}}_6(\mathrm{g})}^{\circ }$ is _______ $\mathrm{kJ}\mathrm{mol}{}^{-1}$ (Nearest integer).