S ( g )+3/2 O 2 ( g ) rightarrow SO 3 ( g )+2 xkcal SO 2 ( g )+1/2 O 2 ( g ) rightarrow SO 3 ( g )+ y kcal The heat of formation of SO 2 ( g ) is given by :

Chemistry · Thermodynamics & Thermochemistry

JEE Main 2025 — 24 January, Evening Shift — Question 37

$\mathrm{S}(\mathrm{g})+\frac{3}{2} \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{SO}_{3}(\mathrm{~g})+2 \mathrm{xkcal}$

$\mathrm{SO}_{2}(\mathrm{~g})+\frac{1}{2} \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{SO}_{3}(\mathrm{~g})+\mathrm{y} \mathrm{kcal}$

The heat of formation of $\mathrm{SO}_{2}(\mathrm{~g})$ is given by :

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

Answer: B

Step-by-step solution

$\underset{(\mathrm{g})}{\mathrm{SO}_{2}}+\frac{1}{2} \underset{(\mathrm{~g})}{\mathrm{O}_{2}} \longrightarrow \underset{(\mathrm{~g})}{\mathrm{SO}_{3}} \quad \Delta \mathrm{H}=-\mathrm{y}$

$\Delta \mathrm{H}_{\mathrm{r}}=\left(\Delta \mathrm{H}_{\mathrm{f}}\right)_{\mathrm{SO}_{3}}-\left(\Delta \mathrm{H}_{\mathrm{f}}\right)_{\mathrm{SO}_{2}}$

$-\mathrm{y}=-2 \mathrm{x}-\left(\Delta \mathrm{H}_{\mathrm{f}}\right)_{\mathrm{SO}_{2}}$

$\left(\Delta \mathrm{H}_{\mathrm{f}}\right)_{\mathrm{SO}_{2}}=\mathrm{y}-2 \mathrm{x}$

Option (2)

Answer key and solution verified before publishing.

Practise Thermodynamics & Thermochemistry

Start with this question, then two more from the same chapter — with a tutor that explains every step. Free.

Solve a similar one free

Exam: JEE Main 2025
Paper: 24 January, Evening Shift
Subject: Chemistry
Chapter: Thermodynamics & Thermochemistry
Topic: Thermochemistry and Enthalpy Changes