Nernst Equation for Cell Potential

Cell Potential (E_cell)

The difference in electric potential between the two electrodes of an electrochemical cell, representing the driving force of the redox reaction.

Standard Cell Potential (E°_cell)

The cell potential when all reactants and products are in their standard states (1 M concentration for solutions, 1 atm pressure for gases, at 298 K).

Reaction Quotient (Q)

A measure of the relative amounts of products and reactants present in a reaction at any given time. It has the same form as the equilibrium constant expression but uses non-equilibrium concentrations.

Faraday Constant (F)

The magnitude of electric charge per mole of electrons, approximately 96,485 coulombs per mole.

Nernst Equation

Where E_cell is cell potential, E^o_{cell} is standard cell potential, R is the ideal gas constant, T is temperature in Kelvin, n is the number of moles of electrons transferred, F is the Faraday constant, and Q is the reaction quotient.

E_cell = E^o_{cell} - \frac{RT}{nF} \ln Q

Nernst Equation at 298 K

A commonly used simplified form at 25°C (298 K).

E_cell = E^o_{cell} - \frac{0.0592}{n} \log Q

Reaction Quotient (Q)

For gaseous species, partial pressures are used. For pure solids and liquids, their activity is considered unity and they are omitted.

Q = \frac{\prod [Products]^{stoichiometric\;coefficient}}{\prod [Reactants]^{stoichiometric\;coefficient}}

Standard Cell Potential

Calculated using standard reduction potentials.

E^o_{cell} = E^o_{cathode} - E^o_{anode}