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ChemistryJEE Main 22 Jan 2026, Shift 1·Q25·Numerical·Moderate

Thermodynamics · Gibbs energy and degree of dissociation

Dissociation of a gas AX2\ce{A2} takes place according to the following chemical reactions. At equilibrium, the total pressure is 1 bar at 300K.

AX2(g)⇌2 A(g)\ce{A2(g) <=> 2A(g)}

The standard Gibbs energy of formation of the involved substances has been provided below:

SubstanceΔGf∘\Delta G_\mathrm{f}^\circ / kJ mol−1^{-1}
AX2\ce{A2}−100.00-100.00
A−50.832-50.832

The degree of dissociation of AX2(g)\ce{A2(g)} is given by (x×10−2)1/2(x\times10^{-2})^{1/2} where xx = . (Nearest integer).

[Given : R=8R = 8 J mol−1^{-1} K−1^{-1}, log⁡2=0.3010\log 2 = 0.3010, log⁡3=0.48\log 3 = 0.48]

We corrected a printing error in the original paper

Source printed the table heading as “ΔGt∘\Delta G_\mathrm{t}^\circ” (subscript t for f, formation).

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See the full 22 Jan 2026, Shift 1 paper