From the following data $$ \begin{aligned} & \mathrm{CH}_3 \mathrm{OH}(l)+\frac{3}{2} \mathrm{O}_2(g)…

From the following data $$ \begin{aligned} & \mathrm{CH}_3 \mathrm{OH}(l)+\frac{3}{2} \mathrm{O}_2(g) \longrightarrow \mathrm{CO}_2(g)+2 \mathrm{H}_2 \mathrm{O}(l) \\ & \Delta_r H^{\circ}=-726 \mathrm{~kJ} \mathrm{~mol}^{-1} \\ & \mathrm{H}_2(g)+\frac{1}{2} \mathrm{O}_2(g) \longrightarrow \mathrm{H}_2 \mathrm{O}(l) \text {; } \\ & \Delta_r \mathrm{H}^{\circ}=-286 \mathrm{~kJ} \mathrm{~mol}^{-1} \\ & \mathrm{C}(\text { graphite })+\mathrm{O}_2(\mathrm{~g}) \longrightarrow \mathrm{CO}_2(\mathrm{~g}) \text {; } \\ & \Delta_r \mathrm{H}^{\circ}=-393 \mathrm{~kJ} \mathrm{~mol}^{-1} \\ & \end{aligned} $$ The standard enthalpy of formation of $\mathrm{CH}_3 \mathrm{OH}(l)$ in $\mathrm{kJ} \mathrm{mol}^{-1}$ is
  1. -239
  2. 239
  3. 547
  4. -905

Solution


$\begin{aligned} & \text { From Eq. (ii) }+ \text { (iii) - Eq. (i) } \\ & \begin{aligned}-286 \times 2-393-(-726)=7 & =-572-393+726 \\ & =-965+726 \\ & =-239 \mathrm{~kJ} / \mathrm{mol}\end{aligned}\end{aligned}$

Asked in: AP EAMCET 2018 (22 Apr Shift 1)

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