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In electrochemistry, the Nernst equation is a chemical thermodynamical relationship that permits the calculation of the reduction potential of a reaction (half-cell or full cell reaction) from the standard electrode potential, absolute temperature, the number of electrons involved in the redox reaction, and activities (often approximated by concentrations) of the chemical species undergoing ...
Related to the Faraday constant is the "faraday", a unit of electrical charge. Its use is much less common than of the coulomb, but is sometimes used in electrochemistry. [4] One faraday of charge is the charge of one mole of elementary charges (or of negative one mole of electrons), that is, 1 faraday = F × 1 mol = 9.648 533 212 331 001 84 × ...
at constant temperature and pressure, the thermodynamic voltage (minimum voltage required to drive the reaction) is given by the Nernst equation: = = where is the Gibbs energy and F is the Faraday constant. The standard thermodynamic voltage (i.e. at standard temperature and pressure) is given by:
The Nernst–Planck equation is a conservation of mass equation used to describe the motion of a charged chemical species in a fluid medium. It extends Fick's law of diffusion for the case where the diffusing particles are also moved with respect to the fluid by electrostatic forces. [1] [2] It is named after Walther Nernst and Max Planck.
At chemical equilibrium, the reaction quotient Q r of the product activity (a Red) by the reagent activity (a Ox) is equal to the equilibrium constant (K) of the half-reaction and in the absence of driving force (ΔG = 0) the potential (E red) also becomes nul. The numerically simplified form of the Nernst equation is expressed as:
Here n e is the number of electrons (in moles), F is the Faraday constant (in coulombs/mole), and ΔE is the cell potential (in volts). Finally, Nernst divided through by the amount of charge transferred to arrive at a new equation which now bears his name: =
F is the Faraday constant (the charge per mole of electrons), equal to 96,485.3 coulomb·mol −1; p 0 is the standard pressure: 1 bar = 10 5 Pa; Note: as the system is at chemical equilibrium, hydrogen gas, H 2 (g), is also in equilibrium with dissolved hydrogen, H 2 (aq), and the Nernst equation implicitly takes into account the Henry's law for
The internal electrolyte is at fixed composition and the electrode response is given by the Nernst equation: E = E 0 − RT/F ln a F −, where: E is the measured cell potential, E 0 is the standard cell potential, R is the ideal gas constant, T is the temperature in kelvins, F is the Faraday constant (9.6485309×10 4 C/mol).