Determine the equilibrium constant, keq, at 25°c for the reaction 2br - (aq) + i2 (s) br2 (l) + 2i - (aq).

Electrochemical cell representation for above reaction is,

Br-/Br2//I2/I-

Reaction at Anode: Br2 + 2e - → 2Br - (1)

Reaction at Cathode: 2I - → I2 + 2e - (2)

Standard reduction potential for Reaction 1 = Ered (anode) = 1.066 v

Standard reduction potential for Reaction 2 = Ered (cathode) = 0.535 v

Eo cell = Ered (cathode) - Ered (anode)

= 0.535 - 1.066

= - 0.531v

Now, we know that ΔGo = - nF (Eo cell) ... (3)

Also, ΔGo = RTln (K) ... (4)

Equation 3 and 4 we get,

ln (K) = nF (Eo cell) / RT

= 2 X 96500 X (-0.531) / (8.314 X 298)

∴ K = 1.085 X 10^-18.