Answer:
See Explanation
Explanation:
In thermodynamics theory the Free Energy (ΔG) of a chemical system is described by the expression ΔG = ΔG° + RTlnQ. When chemical system is at equilibrium ΔG = 0. Substituting into the system expression gives ...
0 = ΔG° + RTlnKc, which rearranges to ΔG° = - RTlnKc. ΔG° in electrochemical terms gives ΔG° = - nFE°, where n = charge transfer, F = Faraday Constant = 96,500 amp·sec and E° = Standard Reduction Potential of the electrochemical system of interest.
Substituting into the ΔG° expression above gives
-nFE°(cell) = -RTlnKc => E°(cell) = (-RT/-nF)lnKc = (2.303·R·T/n·F)logKc
=> E°(cell) = (0.0592/n)logKc = E°(Reduction) - E°(Oxidation)
Application example:
Calculate the Kc value for a Zinc/Copper electrochemical cell.
Zn° => Zn⁺² + 2e⁻ ; E°(Zn) = -0.76 volt
Cu° => Cu⁺² + 2e⁻ ; E°(Cu) = 0.34 volt
By natural process, charge transfer occurs from the more negative reduction potential to the more positive reduction potential.
That is,
Zn° => Zn⁺² + 2e⁻ (Oxidation Rxn)
Cu⁺² + 2e⁻ => Cu° (Reduction Rxn)
E°(Zn/Cu) = (0.0592/n)logKc
= (0.0592/2)logKc = E°(Cu) - E°(Zn) = 0.34v - (-0.76v) = 1.10v
=> logKc = 2(1.10)/0.0592 = 37.2
=> Kc = 10³⁷°² = 1.45 x 10³⁷
