## Equilibrium Constant from Electrode Potentials

1. The problem statement, all variables and given/known data

Evaluate the equilibrium constant for the formation of triodide ion.

I2 + I- ------> I3-

a 298K, if EI2|I-o = 0.6197V and EI3-|I-o=0.5355V

I don't understand one thing - At equilibrium, ΔG=0 so that Eocell=0 (from the equation ΔG=-nfE) but Eocell is not zero for the above reaction. Where is my mistake?

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 Quote by Abdul Quadeer I don't understand one thing - At equilibrium, ΔG=0 so that Eocell=0 (from the equation ΔG=-nfE) but Eocell is not zero for the above reaction. Where is my mistake?
$$\Delta$$Go = -nFEo and $$\Delta$$G = -nFE are two different equations.You are combining them.At equilibrium $$\Delta$$G=0 doesn't
mean that Eo=0 but it means E=0 i.e. electric potential at that time is equal to zero.Eo is constant quantity for any reaction and if it becomes zero the reaction can't proceed.

For calculation of equilibrium constant just use the above result in nerst equation ie at equilibrium

E = Eo - (0.059*logQ)/n = 0 [Q= equilibrium constant]

 Thank you very much.