# Nernst Equation

(Difference between revisions)
 Revision as of 15:29, 15 November 2010 (view source)← Older edit Revision as of 13:57, 24 October 2012 (view source)Newer edit → Line 1: Line 1: − '''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).http://nobelprize.org/nobel_prizes/chemistry/laureates/1920/nernst-bio.html, The Nobel Prize in Chemistry 1920; Walther Nernst
+ '''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).http://nobelprize.org/nobel_prizes/chemistry/laureates/1920/nernst-bio.html, The Nobel Prize in Chemistry 1920; Walther Nernst
== Equation  == == Equation  == Line 5: Line 5: Nernst equation can be expressed as follows: Nernst equation can be expressed as follows: − [[Image:Nernst equation1.png|354x85px]]
+ [[Image:Nernst equation1.png|354x85px|Nernst equation1.png]]
− where
+ where
Ecell is the half-cell potential difference Ecell is the half-cell potential difference Line 15: Line 15: R is the [[Universal gas constant|universal gas constant]]; R = 8.314471 J K-1 mol-1 R is the [[Universal gas constant|universal gas constant]]; R = 8.314471 J K-1 mol-1 − T is the thermodynamics temperature, in ''[[Kelvin|Kelvin]]''; 0 K = -273.15oC
+ T is the thermodynamics temperature, in ''[[Kelvin|Kelvin]]''; 0 K = -273.15oC
− z is the number of [[Moles|moles]] of [[Electrons|electrons]] transferred between cells (defined by the valency of [[Ion|ions]])
+ z is the number of [[Moles|moles]] of [[Electrons|electrons]] transferred between cells (defined by the valency of [[Ion|ions]])
− F is the [[Faraday's constant|Faraday's constant]]; F = 96,485.3415 C mol-1
+ F is the [[Faraday's constant|Faraday's constant]]; F = 96,485.3415 C mol-1
− [red] is the concentration of [[Ion|ion]] that gained [[Electrons|electrons]] ([[Reduction|reduction]])
+ [red] is the concentration of [[Ion|ion]] that gained [[Electrons|electrons]] ([[Reduction|reduction]])
− [oxi] is the concentration of [[Ion|ion]] that lost [[Electrons|electrons]] ([[Oxidation|oxidation]])
+ [oxi] is the concentration of [[Ion|ion]] that lost [[Electrons|electrons]] ([[Oxidation|oxidation]])
− == Membrane potential
== + == Membrane potential
== ''Main article: ''[[Membrane Potential|Membrane potential]] ''Main article: ''[[Membrane Potential|Membrane potential]] − 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:
+ 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:
− [[Image:Nernst equation2.png|278x98px]]
+ [[Image:Nernst equation2.png|278x98px|Nernst equation2.png]]
− or
+ or
− [[Image:Nernst equation3.png|371x97px]]
+ [[Image:Nernst equation3.png|371x97px|Nernst equation3.png]]
− where
+ where
Em is the potential difference of an ion between membranes Em is the potential difference of an ion between membranes Line 49: Line 49: F is the Faraday's constant; F = 96,485.3415 C mol-1 F is the Faraday's constant; F = 96,485.3415 C mol-1 − [A-]o is the concentration of ion outside the membrane (in this case is anion, negative charge ion)
+ [A-]o is the concentration of ion outside the membrane (in this case is anion, negative charge ion)
− [A-]i is the concentration of ion inside the membrane (in this case is anion, negative charge ion) + [A-]i is the concentration of ion inside the membrane (in this case is anion, negative charge ion) == Application  == == Application  == − === Ussing study of frog skin  === + === 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.
+ 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.
[[Image:Ussing model.png|629x322px|Ussing model of transepithelial ions absorption.]] [[Image:Ussing model.png|629x322px|Ussing model of transepithelial ions absorption.]] − Diagram based on CMB2003: Cell and Membrane Transport lecture note (2010).Ussing model of transepithelial ions absorption.
+ Diagram based on CMB2003: Cell and Membrane Transport lecture note (2010).Ussing model of transepithelial ions absorption.
− For example at the standard condition and temperature of 25oC (298K), the above sodium ion membrane potential can be calculated as:
+ For example at the standard condition and temperature of 25oC (298K), the above sodium ion membrane potential can be calculated as:
+ *[[Membrane potential]]
*[[Goldman equation]]
*[[Goldman equation]]
− == References & Notes
== + == References & Notes
== −
+
== External Links  == == External Links  == *[http://www.nernstgoldman.physiology.arizona.edu/ The Nernst/Goldman Equation Simulator] *[http://www.nernstgoldman.physiology.arizona.edu/ The Nernst/Goldman Equation Simulator]

## Revision as of 13:57, 24 October 2012

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).[1]

## 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

Main article: 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-]o is the concentration of ion outside the membrane (in this case is anion, negative charge ion)

[A-]i is the concentration of ion inside the membrane (in this case is anion, negative charge ion)

## 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.

[2]Ussing model of transepithelial ions absorption.

For example at the standard condition and temperature of 25oC (298K), the above sodium ion membrane potential can be calculated as:

### Goldman equation

Main article: Goldman equation

In presence of more than one ion, the Nernst equation can be modified into Hodgkin-Katz-Goldman equation or is commonly known as Goldman equation. Goldman equation is proposed by David E. Goldman of Columbia University together with Alan L. Hodgkin and Bernard Katz.