Electrochemistry : Nernst Equation and Faraday's Law 
Let's review what occurs in a galvanic cell:
A reaction may start at standardstate conditions, but as the reaction proceeds, the concentrations of the solutions change, the driving force behind the reaction becomes weaker, and the cell potential eventually reaches zero.
 The zinc electrode is losing mass as Zn metal is oxidized to Zn^{2+} ions which go into solution.
 The concentration of the Zn^{2+} solution is increasing.
 Anions, negative ions (e.g. Cl^{}), are flowing from the salt bridge toward the anode to balance the positive charge of the Zn^{2+} ions produced.
 The copper electrode is gaining mass as Cu^{2+} ions in the solution are reduced to Cu metal.
 The concentration of the Cu^{2+} solution is decreasing.
 Cations, positive ions (e.g. K^{+}), are flowing from the salt bridge toward the cathode to replace the positive charge of the Cu^{2+} ions that consumed.
**When the cell potential equals zero, the reaction is at equilibrium.
Nernst Equation  Can be used to find the cell potential at any moment in during a reaction or at conditions other than standardstate.
E = cell potential (V) under specific conditionsSince the temperature is generally 25C (298 K), three of the terms in the above Nernst equation can be considered constants: R, T, and F. Substituting the values of these constants, results in the following equation:E= cell potential at standardstate conditions
R = ideal gas constant = 8.314 J/molK
T = temperature (kelvin), which is generally 25C (298 K)
n = number of moles of electrons transferred in the balanced equation
F = Faraday's constant, the charge on a mole of electrons = 95,484.56 C/mol
lnQ_{c} = the natural log of the reaction quotient at the moment in time
Reaction quotient (Q_{c})  The mathematical product of the concentrations of the products of the reaction divided by the mathematical product of the concentrations of the reactants. For the reaction:
There is a transfer of 2 electrons, so n = 2.
At equilibrium E = 0 and Q_{c} = K_{c:}
The Nernst equation can be rearranged as follows:
This equation can be used to calculate the equilibrium constant for any oxidationreduction reaction from its standardstate cell potential.
Sample Calculation
Calculate the cell potential for the following system:
Write the halfreactions with the halfcell potentials:
Multiply the reactions to get the lowest common multiple of electrons:

Faraday's Law  The amount of substance consumed
or produced at one of the electrodes in an electrolytic cell is directly
proportional to the amount of electricity that passes through the cell.
By definition, one coulomb (C) of charge is transferred when a oneampere (amp) current flows for one second (s): Faraday's Constant  The charge on a mole of electrons:

Michael Faraday 