Verified Solution • 2025–26 Session moderate

QJEEM18Chda7a: JEE Main 2018 Chemistry - Class 11 JEEM18Chda7a Solution: At 320 K, a gas A 2 is 20% dissociated to A(g). The standard…

At 320 K, a gas A2 is 20% dissociated to A(g). The standard free energy change at 320 K and 1 atm in J mol-1 is approximately : (R = 8.314 JK-1 mol-1; ln2 = 0.693; ln 3 = 1.098)

Multiple Choice Options

  • A 4763
  • B 2068
  • C 1844
  • D 4281

Step-by-Step Verified Solution

A2 (g) ⇌\rightleftharpoons 2 A (g)

Assume initially concentration of A2 = [A2] = 1 m

at equilibrium [A2] = 1 ×\times 80100{{80} \over {100}} = 0.8 M

and 20% of [A2] = 1 ×\times 20100{{20} \over {100}} = 0.2 M

∴    \therefore\,\,\,\, [A] = 2 ×\times 0.2 = 0.4 M

Equilibrium constant

K = [A]2[A2]{{{{[A]}^2}} \over {[{A_2}]}} = [0.4]2[0.8]{{{{\left[ {0.4} \right]}^2}} \over {\left[ {0.8} \right]}} = 0.2

Δ\Delta Go = −- RT ℓ\ell nK

= −- 8.314 ×\times 320 ×\times ℓ\ell n(0.2)

= 4281 J/mol.

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