Value of the equilibrium constant?

Question

What is the value of the equilibrium constant for the reaction between each pair at 25°C?

(a) I2(s) and Br -(aq)

(b) Ni(s) and Ag+(aq)

Answer 1

(a) I2(s) and Br -(aq)

I2 & 2e-   -->  2I-  @ Eo  =0.536 volts

2 Br-    --> Br2  & 2 e-  @ Eo = -1.065

Eo for this non spontaneous reaction, (electrolytic cell),  is - 0.529

nernst:

E = Eo - (0.0592/n) logQ

nernst @ equilibrium:

0 = Eo - (0.0592/n) logK    or:

Eo =  (0.0592/n) logK

- 0.529 = (0.0592 / 2) (log K)

log K = - 0.529 / 0.0296  = -17.87

your answer:  K = 1.34e-18

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(b) Ni(s) and Ag+(aq)

Ni & 2 Ag+ --> Ni+2  & 2 Ag

Ni  -->   Ni+2  & 2 e-  Eo = + 0.28 volts

Ag+ & 1 e- --> Ag   .. Eo = + 0.799 volts

Eo for this sp0ntaneous reaction (voltaic cell) = 1.079 volts

Eo =  0.0592/n logK

1.079 = (0.0592 / 2) (log K)

log K = 1.079 / 0.0296  = 36.45

your answer:  K = 2.8e36