# Nernst Equation

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− where + where + + + + Em is the potential difference of an ion between membranes + + R is the universal gas constant; R = 8.314471 J mol-1 + + T is the thermodynamics temperature, in ''Kelvin''; 0 K = -273.15oC + + z is the number of moles of electrons transferred between membranes (defined by the valency of ion) + + F is the Faraday's constant; F = 96,485.3415 C mol-1 + + [A-1] is the concentration of ion outside the membrane + + [A-1] is the concentration of ion inside the membrane + + + + == Application == + + === Ussing Study of Frog Skin ===

## Revision as of 21:43, 14 November 2010

Nernst Equation is an equation used to calculate the electrical potential of a chemical reaction. In its equilibrium state, the Nernst equation should be zero. It also shows the direct relation between energy or potential of a cell and its participating ions. The equation is proposed by a German chemist, Walther H. Nernst (1864-1941).

## Equation

Nernst equation can be expressed as follows:

where

Ecell is the half-cell potential difference

Eθcell is the standard half-cell potential

R is the universal gas constant; R = 8.314471 J K-1 mol-1

T is the thermodynamics temperature, in Kelvin; 0 K = -273.15oC

z is the number of moles of electrons transferred between cells (defined by the valency of ions)

F is the Faraday's constant; F = 96,485.3415 C mol-1

[red] is the concentration of ion that gained electrons (reduction)

[oxi] is the concentration of ion that lost electrons (oxidation)

## Membrane Potential

Nernst equation is also can be used to calculate the potential of an ion across the membrane. For potential difference of a membrane, we can manipulate the Nernst Equation as follows:

or

where

Em is the potential difference of an ion between membranes

R is the universal gas constant; R = 8.314471 J mol-1

T is the thermodynamics temperature, in Kelvin; 0 K = -273.15oC

z is the number of moles of electrons transferred between membranes (defined by the valency of ion)

F is the Faraday's constant; F = 96,485.3415 C mol-1

[A-1] is the concentration of ion outside the membrane

[A-1] is the concentration of ion inside the membrane