JEE Main 2023 — Chemistry Physical Chemistry

2023integereasy

${A}_{2}+{B}_{2}\rightarrow 2\mathrm{AB}.\Delta {H}_{f}=-200\mathrm{kJ}{\mathrm{mol}}^{-1}$

$\mathrm{AB},{A}_{2}$ and ${B}_{2}$ are diatomic molecules. If the bond enthalpies of ${A}_{2},{B}_{2}$ and $\mathrm{AB}$ are in the ratio $1:0.5:1,$ then the bond enthalpy of ${A}_{2}$ is $_________kJ{\mathrm{mol}}^{–1}$ (Nearest integer)

Official previous-year question

Held on 13 Apr 2023 · Verified 6 Jul 2026.

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Solution

First write balanced reaction for the formation of one mole of $\mathrm{AB}$ with the help of diatomic molecule:

$\frac{1}{2}{A}_{2}+\frac{1}{2}{B}_{2}\rightarrow \mathrm{AB}{\Delta H}_{f}=-200\mathrm{kJ}/\mathrm{mol}$

Now,

$\Delta {H}_{\mathrm{reaction}}=\frac{1}{2}\Delta {H}_{A-A}+\frac{1}{2}\Delta {H}_{B-B}-\Delta {H}_{\mathrm{AB}}(\mathrm{let},\Delta {H}_{\mathrm{AB}}=x)$

$\frac{1}{2}x+\frac{1}{2}(0.5x)-x=-200\Rightarrow \frac{x}{2}+0.25x-x=-200$

$\Rightarrow -0.25x=-200\Rightarrow x=800\mathrm{kJ}/\mathrm{mol}$

Bond enthalpy $=800\mathrm{kJ}/\mathrm{mol}.$

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JEE Main 2023 — Chemistry Physical Chemistry

2023integereasy

${A}_{2}+{B}_{2}\rightarrow 2\mathrm{AB}.\Delta {H}_{f}=-200\mathrm{kJ}{\mathrm{mol}}^{-1}$

Official previous-year question

Held on 13 Apr 2023 · Verified 6 Jul 2026.

Did you get this right?

Solution

First write balanced reaction for the formation of one mole of $\mathrm{AB}$ with the help of diatomic molecule:

$\frac{1}{2}{A}_{2}+\frac{1}{2}{B}_{2}\rightarrow \mathrm{AB}{\Delta H}_{f}=-200\mathrm{kJ}/\mathrm{mol}$

Now,

$\Delta {H}_{\mathrm{reaction}}=\frac{1}{2}\Delta {H}_{A-A}+\frac{1}{2}\Delta {H}_{B-B}-\Delta {H}_{\mathrm{AB}}(\mathrm{let},\Delta {H}_{\mathrm{AB}}=x)$

$\frac{1}{2}x+\frac{1}{2}(0.5x)-x=-200\Rightarrow \frac{x}{2}+0.25x-x=-200$

$\Rightarrow -0.25x=-200\Rightarrow x=800\mathrm{kJ}/\mathrm{mol}$

Bond enthalpy $=800\mathrm{kJ}/\mathrm{mol}.$

Your note

JEE Main Physical Chemistry in other years

Keep practicing Physical Chemistry

Work through every JEE Main Physical Chemistry PYQ, year by year.

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JEE Main 2023 — Chemistry Physical Chemistry

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Solution

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JEE Main Physical Chemistry in other years

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Organic Chemistry

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JEE Main 2023 — Chemistry Physical Chemistry

Did you get this right?

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

Keep practicing Physical Chemistry