Skip to content
dronacharya.ai
← JEE Main 2022 · 26 Jun · Shift 2
ChemistryInteger+4 / -1Question 86 of 90

JEE Main 2022 · 26 Jun · Shift 2, Chemistry question 86

40% of HI undergoes decomposition to H2\mathrm{H_2} and I2\mathrm{I_2} at 300 K. ΔG⊖\Delta G^\ominus for this decompostion reaction at one atmopsphere pressure is ______ J mol−1^{-1}. [nearest integer]

(Use R=8.31R=8.31 J K−1^{-1} mol−1^{-1}; log⁡2=0.3010\log2=0.3010, ln⁡10=2.3\ln10=2.3, log⁡3=0.477\log3=0.477)

Answer and worked solution

Official answer: 2735

Per mole of HI (HI⇌12H2+12I2\mathrm{HI\rightleftharpoons\frac12H_2+\frac12I_2}, as the key takes it): from 1 mol, 0.6 HI, 0.2 H2\mathrm{H_2}, 0.2 I2\mathrm{I_2}; K=(0.2)1/2(0.2)1/20.6=13K=\dfrac{(0.2)^{1/2}(0.2)^{1/2}}{0.6}=\dfrac13.

Free energy. ΔG⊖=−RTln⁡K=8.31×300×2.3×0.477≈2735\Delta G^\ominus=-RT\ln K=8.31\times300\times2.3\times0.477\approx2735 J mol−1^{-1}.

Note. Written as 2HI⇌H2+I2\mathrm{2HI\rightleftharpoons H_2+I_2} the value doubles (about 5470); the key uses one mole of HI.

Answer: 2735

Topics:Equilibrium and Gibbs energyLaw of mass action and Kc, Kp
← Previous questionNext question →