Q20 / 75 · JEE Main 2025 (24 Jan Shift 2) · Chemistry

$\begin{aligned} & \mathrm{S}(\mathrm{~g})+\frac{3}{2} \mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{SO}_3(\mathrm{~g})+2 x \mathrm{kcal} \\ & \mathrm{SO}_2(\mathrm{~g})+\frac{1}{2} \mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{SO}_3(\mathrm{~g})+y \mathrm{kcal} \end{aligned}$ The heat of formation of $\mathrm{SO}_2(\mathrm{~g})$ is given by :

  • A
    $x+y \mathrm{kcal}$
  • Correct answer
    B
    $y-2 x \mathrm{kcal}$
  • C
    $\frac{2 x}{y} \mathrm{kcal}$
  • D
    $2 x+y \mathrm{kcal}$

Solution

(i) $\mathrm{S}(\mathrm{g})+\frac{3}{2} \mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{SO}_3(\mathrm{~g})+2 x$ kcal $\Delta \mathrm{H}_1$ (ii) $\mathrm{SO}_2(\mathrm{~g})+\frac{1}{2} \mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{SO}_3(\mathrm{~g})+y$ kcal $\Delta \mathrm{H}_2$ (i) - (ii) $\begin{aligned} & \mathrm{S}(\mathrm{~g})+\mathrm{O}_2(\mathrm{~g}) \rightarrow \mathrm{SO}_2(\mathrm{~g}) \Delta \mathrm{H} \\ & \Delta \mathrm{H}=\Delta \mathrm{H}_1-\Delta \mathrm{H}_2 \\ & =-2 x-(-y)=(y-2 x) \mathrm{kcal} \end{aligned}$

Hence, the correct answer is option: 'B'.

Relevant Questions