Calculate ΔGrxn at 25 °C for the process AgI(s) ⇌ Ag+(aq) + I- (aq)?

NetherCraft 0

The solubility product constant at 25°C for AgI(s) in water has the value 8.3 × 10-17

[Ag+] = 9.1 × 10-9 and [I-] = 9.1 × 10-9.

A) -4.4 kJ/mol

B) +91.7 kJ/mol

C) 0.0 kJ/mol

D) +4.4 kJ/mol

E) -91.7 kJ/mol

And the answer is C) 0.0 kJ/mol, but I don’t know why ? Because when I solved I got -91.7

Thank you.

2 Answers

  • AgI(s) ⇌ Ag+(aq) + I- (aq)

    Ksp = [Ag++][I-] = 9.1×10^-9 x 9.1×10^-9 = 8.3 x 10^-17

    So the reaction is in equilibrium. And for an equilibrium reaction ΔGrxn = 0. Hence the option C) is correct.

  • If you use ∆G = -RT lnK then one gets

    ∆G = -(8.314)(298)(2.303)(log8.3×10^-17) = -5705.85 x log 8.3×10^-17

    ∆G = -5705.85 x -16.08 = +91750 J = + 91.7 kJ

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