Nernst equation and its application to chemical cells

Nernst Equation

An equation that relates the electrode potential of an electrochemical cell to the concentrations of the reactants and products.

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.

Standard Cell Potential (E°_cell)

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

Nernst Equation (General Form)

R = 8.314 J/mol.K, T = temperature in Kelvin, n = moles of electrons, F = 96485 C/mol, Q = reaction quotient.

E_cell = E⁰_{cell} - \frac{RT}{nF} \ln Q

Nernst Equation (at 298 K)

This simplified form is commonly used for calculations at standard room temperature.

E_cell = E⁰_{cell} - \frac{0.0592}{n} \log Q

Reaction Quotient (Q)

For a reaction aA + bB ≤> cC + dD, Q = ([C]^c [D]^d) / ([A]^a [B]^b). Solids and pure liquids are omitted.

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

Standard Cell Potential

Using standard reduction potentials.

E⁰_{cell} = E⁰_{cathode} - E⁰_{anode}