Term information
In electrochemistry, the Nernst equation is an equation that can be used (in conjunction with other information) to determine the equilibrium reduction potential of a half-cell in an electrochemical cell. It can also be used to determine the total voltage (electromotive force) for a full electrochemical cell. ... The two (ultimately equivalent) equations for these two cases (half-cell, full cell) are as follows: E_\text{red} = E^{\ominus}_\text{red} - \frac{RT}{zF} \ln\frac{a_\text{Red}}{a_\text{Ox}} (half-cell reduction potential) E_\text{cell} = E^{\ominus}_\text{cell} - \frac{RT}{zF} \ln Q (total cell potential) where * Ered is the half-cell reduction potential at the temperature of interest * Eored is the standard half-cell reduction potential * Ecell is the cell potential (electromotive force) * Eocell is the standard cell potential at the temperature of interest * R is the universal gas constant: R = 8.314 1 * T is the absolute temperature * a is the chemical activity for the relevant species, where aRed is the reductant and aOx is the oxidant. aX = XcX, where X is the activity coefficient of species X. (Since activity coefficients tend to unity at low concentrations, activities in the Nernst equation are frequently replaced by simple concentrations.) * F is the Faraday constant, the number of coulombs per mole of electrons: F = 9.648 104 C1 * z is the number of moles of electrons transferred in the cell reaction or half-reaction * Q is the reaction quotient. source: http://en.wikipedia.org/wiki/Nernst_equation