# Nernst Equation

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− | '''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).<br> | + | '''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 [[Ion|ions]]. The equation is proposed by a German chemist, Walther H. Nernst (1864-1941).<br> |

== Equation == | == Equation == | ||

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E<sup>θ<sub></sub></sup><sub>cell </sub>is the standard half-cell potential | E<sup>θ<sub></sub></sup><sub>cell </sub>is the standard half-cell potential | ||

− | R is the universal gas constant; R = 8.314471 J K<sup>-1</sup> mol<sup>-1</sup> | + | R is the [[Universal gas constant|universal gas constant]]; R = 8.314471 J K<sup>-1</sup> mol<sup>-1</sup> |

− | T is the thermodynamics temperature, in ''Kelvin''; 0 K = -273.15<sup>o</sup>C<br> | + | T is the thermodynamics temperature, in ''[[Kelvin|Kelvin]]''; 0 K = -273.15<sup>o</sup>C<br> |

− | z is the number of moles of electrons transferred between cells (defined by the valency of ions)<br> | + | z is the number of [[Moles|moles]] of [[Electrons|electrons]] transferred between cells (defined by the valency of [[Ion|ions]])<br> |

− | F is the Faraday's constant; F = 96,485.3415 C mol<sup>-1</sup><br> | + | F is the [[Faraday's constant|Faraday's constant]]; F = 96,485.3415 C mol<sup>-1</sup><br> |

− | [red] is the concentration of ion that gained electrons (reduction)<br> | + | [red] is the concentration of [[Ion|ion]] that gained [[Electrons|electrons]] ([[Reduction|reduction]])<br> |

− | [oxi] is the concentration of ion that lost electrons (oxidation)<br> | + | [oxi] is the concentration of [[Ion|ion]] that lost [[Electrons|electrons]] ([[Oxidation|oxidation]])<br> |

== Membrane Potential<br> == | == Membrane Potential<br> == | ||

− | 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:<br> | + | Nernst equation is also can be used to calculate the potential of an [[Ion|ion]] across the membrane. For potential difference of a membrane, we can manipulate the Nernst Equation as follows:<br> |

[[Image:Nernst equation2.png|278x98px]]<br> | [[Image:Nernst equation2.png|278x98px]]<br> |

## Revision as of 22:02, 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).

## Contents |

## Equation

Nernst equation can be expressed as follows:

where

E_{cell }is the half-cell potential difference

E^{θ}_{cell }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 = -273.15^{o}C

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

E_{m} 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 = -273.15^{o}C

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

### Using Study of Frog Skin

In biochemistry, Nernst equation can be used to calculate the potential difference of ion between membranes. Hans H. Ussing, a Danish scientist, used a frog skin to measure the potential difference of sodium and potassium ions across the membranes with his famous invention, the Ussing chamber.