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ChemistryInteger+4 / -1Question 74 of 75

JEE Main 2026 · 6 Apr · Shift 2, Chemistry question 74

In a closed flask at 600 K, one mole of XX2YX4(g)\ce{X2Y4(g)} attains equilibrium as given below :

XX2YX4(g)⇌2 XYX2(g)\ce{X2Y4(g) <=> 2XY2(g)}

At equilibrium, 75% XX2YX4(g)\ce{X2Y4(g)} was dissociated and the total pressure is 1 atm. The magnitude of ΔrG⊖\Delta_rG^\ominus (in kJ mol−1^{-1}) at this temperature is ________. (Nearest Integer)

(Given : R = 8.3 J mol−1^{-1} K−1^{-1}; ln 10 = 2.3, log 2 = 0.3, log 3 = 0.48, log 5 = 0.69, log 7 = 0.84)

Answer and worked solution

Official answer: 8

Equilibrium. From 1 mol XX2YX4\ce{X2Y4}: 0.25 mol XX2YX4\ce{X2Y4} and 1.5 mol XYX2\ce{XY2}, total 1.75 mol at 1 atm.
Kp=(6/7)21/7=367,log⁡Kp=0.78×2−0.84=0.72.K_p=\frac{(6/7)^2}{1/7}=\frac{36}7,\qquad\log K_p=0.78\times2-0.84=0.72.

Free energy.
ΔrG∘=−2.3×8.3×600×0.72≈−8247 J mol−1.\Delta_rG^\circ=-2.3\times8.3\times600\times0.72\approx-8247\text{ J mol}^{-1}.

Magnitude: about 8 kJ mol⁻¹.

Answer: 8

Topics:Equilibrium and Gibbs energyLaw of mass action and Kc, Kp
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