Nernst Equation Walther Nernst The Nernst equation is an equation that relates the equilibrium reduction potential of a half-cell in an electrochemical cell to the standard electrode potential, temperature, activity, and reaction quotient of the underlying reactions and species used. Walther Nernst This equation is named after the German physical chemist who first formulated it,Walther Nernst.

Nernst Equation

Problem Consider a galvanic cell that uses the reaction: Cu(s) + 2Fe3+(aq) → Cu2+(aq) + 2Fe2+(aq) What is the potential of a cell at 25 °C that has the following ion concentrations? [Fe3+] = 1.0 x 10-4 M [Cu2+] = 0.25 M [Fe2+] = 0.20 M

Solution Reaction quotient is given by: Cell is not under standard conditions, so the Nernst Equation must be used:

Solution Eocell = Eocathode – Eoanode Eocell = 0.77 V – 0.34 V = 0.43 V n = 2 since 2 electrons are transferred

Problem Calculate the equilibrium constant of the reaction: Cu(s) + 2Ag+(aq) → Cu2+ (aq) + 2Ag(s) Eo cell = 0.46 V

Solution

Problem The standard electrode potential for Daniell cell is 1.1V. Calculate the standard Gibbs energy for the reaction: Zn(s) + Cu2+(aq) ⎯→ Zn2+(aq) + Cu(s)

Solution ΔrGo = – nFEocell n =2, F = 96487 C mol-1, Eocell = 1.1 V