Nernst Equation

Nernst Equation - Nernst equation From Wikipedia, the free...

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Nernst equation From Wikipedia, the free encyclopedia In electrochemistry, the Nernst equation is an equation which 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 Frst formulated it, Walther Nernst. [1][2] Contents 1 Expression 2 Nernst potential 3 Derivation 3.1 Using Boltzmann factors 3.2 Using entropy and Gibbs energy 4 Relation to equilibrium 5 Limitations 6 See also 7 References 8 External links Expression The two (ultimately equivalent) equations for these two cases (half-cell, full cell) are as follows: (half-cell reduction potential) (total cell potential) where E red is the half-cell reduction potential E o red is the standard half-cell reduction potential E cell is the cell potential (electromotive force) E o cell is the standard cell potential R is the universal gas constant: R = 8.314 472(15) J K 1 mol 1 T is the absolute temperature a is the chemical activity for the relevant species. a X = γ X c X , where γ X is the activity coefFcient of species X. (Since activity coefFcients tend to unity at low concentrations, activities in the Nernst
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equation are frequently replaced by simple concentrations.) F is the Faraday constant, the number of coulombs per mole of electrons: F = 9.648 533 99(24) × 10 4 C mol 1 z is the number of electrons transferred in the cell reaction or half-reaction Q is the reaction quotient. At room temperature (25 °C), RT/F may be treated like a constant and replaced by 25.693 mV for cells. The Nernst equation is frequently expressed in terms of base 10 logarithms ( i.e. , common logarithms) rather than natural logarithms, in which case it is written, for a cell at 25 °C : The Nernst equation is used in physiology for ±nding the electric potential of a cell membrane with respect to one type of ion. Nernst potential
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Nernst Equation - Nernst equation From Wikipedia, the free...

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