Q.Write expressions to calculate equilibrium constant from i. Concentration data ii. Thermochemical data iii. Electrochemical data

The same equilibrium constant $K$ can be reached from three independent kinds of data -- equilibrium concentrations, thermochemical data ($\Delta G^0$), or electrochemical data ($E^0_{cell}$). …

Step 1 (Concentration data). For a general reaction $a\mathrm{A} + b\mathrm{B} \rightleftharpoons c\mathrm{C} + d\mathrm{D}$, the law of mass action gives the equilibrium constant directly from the equilibrium concentrations:

Step 2 (Thermochemical data). Thermodynamics relates the standard Gibbs energy change of the reaction to $K$:

so knowing $\Delta G^0$ (from thermochemical tables) gives $\log_{10} K = \dfrac{-\Delta G^0}{2.303\,RT}$ and $K$ by taking the antilog.

Step 3 (Electrochemical data). Combining $\Delta G^0 = -nFE^0_{cell}$ with the relation above gives the chapter's Eq. (5.29): …