Determination of Equilibrium Constants:

From electrode potential measurements, we could compute numerical values of many equilibrium constants such as solubility-product constant, dissociation constants and formation constants. One significant advantage of this method is that the measurements can be made without disturbing any equilibria that may exist in the test solution.

In Unit 1, it was shown that the change in free energy for a reaction can be given by the equation1.23:

ΔG =ΔGº +RT ln a^p_P a^r_R/a^a_A a^b_B

Or ΔG = ΔGº + 2.3RTlog K                                                                 ...(2.39)

where K is equilibrium constant.

In equilibrium condition  Δ G = 0 ,

Δ G^o =  - 2.3RT log K

According to Eq.1.24,  Δ G^o = - nFE^o

Combining both above equations yields

- nFE^o = - 2.3RT log K

And

log K = nFEº_cell/2.3 RT                                                                                ...(2.40)

Substitution for F,R and T,  leads to

log K = nFEº_cell/0.0591                                                                                ...(2.41)