Relation Between Standard Free Energy Change And Equilibrium Constant

∴ K_eq [ as Ecell = 0]

∴ = RT ln K_eq

−ΔG° = RT ln K_eq

∴ ΔG° = −2.303 RT log K_eq

[Note: This relation is valid for any equilibrium constant like Kw, Kp, Kc, Ksp etc.]

Some other important relations involving enthalpy change and entropy change are

(a) ΔH = nF where dE/dT  is called as temperature coefficient representing the change of EMF with the change of temperature, n is the number of moles of electrons involved, F is one Faraday, E is the EMF of cell at temperature T and T is the absolute temperature.

(b) ΔS = nF(dE/dT)

Further Reading : 

1. Electrolysis

2. Concentration Cells

3. Type of Half Cells