JEE Main 2026 — Chemistry Physical Chemistry

2026integermedium

Use the following data :

$\begin{array}{|c|c|c|} \hline \text {Substance } & \frac{\Delta_f \mathrm{H}^{\ominus}(500 \mathrm{~K})}{\mathrm{kJmol}^{-1}} & \frac{\mathrm{~S}^{\ominus}(500 \mathrm{~K})}{\mathrm{JK}^{-1} \mathrm{~mol}^{-1}} \\ \hline \mathrm{AB}(\mathrm{~g}) & 32 & 222 \\ \hline \mathrm{~A}_2(\mathrm{g}) & 6 & 146 \\ \hline \mathrm{~B}_2(\mathrm{g}) & x & 280 \\ \hline \end{array}$

One mole each of $\mathrm{A}_{2}(\mathrm{~g})$ and $\mathrm{B}_{2}(\mathrm{~g})$ are taken in a 1 L closed flask and allowed to establish the equilibrium at 500 K. $\mathrm{A}_{2}(\mathrm{~g})+\mathrm{B}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{AB}(\mathrm{~g})$ The value of $x\left(\mathrm{in} \mathrm{kJ} \mathrm{mol}^{-1}\right)$ is $\_\_\_\_$ . (Nearest integer)

(Given : $\log \mathrm{K}=2.2 \quad \mathrm{R}=8.3 \mathrm{~J} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}$ )

Official previous-year question

Held on 21 Jan 2026 · Verified 6 Jul 2026.

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Solution

Reaction: $A_2(g) + B_2(g) \rightleftharpoons 2AB(g)$

$\Delta G° = -2.303RT \log K = -2.303 \times 8.3 \times 500 \times 2.2 = -21026$ J/mol = $-21.03$ kJ/mol

$\Delta S° = 2(222) - [146 + 280] = 444 - 426 = 18$ J K⁻¹ mol⁻¹

$\Delta H° = 2(32) - [6 + x] = (58 - x)$ kJ/mol

Using $\Delta G° = \Delta H° - T\Delta S°$ :

$-21.03 = (58 - x) - (500 \times 0.018)$

$-21.03 = 58 - x - 9 = 49 - x$

$x = 49 + 21.03 = 70.03 \approx 70$ kJ/mol

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Solution

Reaction: $A_2(g) + B_2(g) \rightleftharpoons 2AB(g)$

$\Delta G° = -2.303RT \log K = -2.303 \times 8.3 \times 500 \times 2.2 = -21026$ J/mol = $-21.03$ kJ/mol

$\Delta S° = 2(222) - [146 + 280] = 444 - 426 = 18$ J K⁻¹ mol⁻¹

$\Delta H° = 2(32) - [6 + x] = (58 - x)$ kJ/mol

Using $\Delta G° = \Delta H° - T\Delta S°$ :

$-21.03 = (58 - x) - (500 \times 0.018)$

$-21.03 = 58 - x - 9 = 49 - x$

$x = 49 + 21.03 = 70.03 \approx 70$ kJ/mol

JEE Main 2026 — Chemistry Physical Chemistry

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JEE Main 2026 — Chemistry Physical Chemistry

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Solution

Your note

JEE Main Physical Chemistry in other years

More JEE Main Physical Chemistry questions

Other Chemistry topics for JEE Main

Organic Chemistry

Inorganic Chemistry

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