The standard heat of formation $\left(\Delta_{f} \mathrm{H}_{298}^{0}\right)$ of ethane (in $\mathrm{kJ} / \mathrm{mol}$ ), if the heat of combustion of ethane, hydrogen and graphite are $-1560,-393.5$ and $-286 \mathrm{~kJ} / \mathrm{mol}$, respectively is __________________ .
$(-192.5)$
$\mathrm{C}+\mathrm{O}_{2} \rightarrow \mathrm{CO}_{2} ; \Delta_{\mathrm{C}} \mathrm{H}^{0}=-286.0 \mathrm{~kJ} / \mathrm{mol}$ ...(i)
$\mathrm{H}_{2}+\frac{1}{2} \mathrm{O}_{2} \rightarrow \mathrm{H}_{2} \mathrm{O} ; \Delta_{\mathrm{C}} \mathrm{H}^{0}=-393.5 \mathrm{~kJ} / \mathrm{mol}$ ....(ii)
$\mathrm{C}_{2} \mathrm{H}_{6}+\frac{1}{2} \mathrm{O}_{2} \rightarrow 2 \mathrm{CO}_{2}+3 \mathrm{H}_{2} \mathrm{O} ; \Delta_{\mathrm{C}} \mathrm{H}^{0}=-1560 \mathrm{~kJ} / \mathrm{mol}$ ....(iii)
$\Delta_{f} \mathrm{H}^{0}$ of $\mathrm{C}_{2} \mathrm{H}_{6}(g)=$
$2 \times \Delta_{\mathrm{C}}^{0} \mathrm{H}\left[\mathrm{C}_{\text {graphite }}\right]+3 \times \Delta_{\mathrm{C}} \mathrm{H}^{0}\left[\mathrm{H}_{2}(g)\right]-\Delta_{\mathrm{C}} \mathrm{H}^{0}\left[\mathrm{C}_{2} \mathrm{H}_{6}(g)\right]$
$=2 \times(-286.0)+3(-393.5)-(-1560)$
$=-192.5 \mathrm{~kJ} / \mathrm{mol}$
Click here to get exam-ready with eSaral
For making your preparation journey smoother of JEE, NEET and Class 8 to 10, grab our app now.