Nernst Equation

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. It is named after the German physical chemist who first formulated it, Walther Nernst.

The Nernst equation gives a formula that relates the numerical values of the concentration gradient to the electric gradient that balances it. For example, if a concentration gradient was established by dissolving KCl in half of a divided vessel that was originally full of H2O, and then a membrane permeable to K+ ions was introduced between the two halves—empirically, an equilibrium situation would arise where the chemical concentration gradient (that would normally cause ions to move from the region of high concentration to the region of low concentration) could be balanced by an electrical gradient that opposes the movement of charge.

Read more about Nernst EquationExpression, Nernst Potential, Relation To Equilibrium, Limitations

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... In dilute solutions, the Nernst equation can be expressed directly in terms of concentrations (since activity coefficients are close to unity) ... This complicates the use of the Nernst equation, since estimation of non-ideal activities of ions generally requires experimental measurements ... The Nernst equation also only applies when there is no net current flow through the electrode ...
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... For a half cell equation, conventionally written as reduction (electrons on the left side) where is the standard Gibbs free energy change, is the number of ... The Nernst equation relates pH and where curly brackets indicate activities and exponents are shown in the conventional manner ... This equation is the equation of a straight line for as a function of pH with a slope of volt (pH has no units.) This equation predicts lower at ...

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