Faraday constant

The Faraday constant is the reduction or oxidation of singly charged ions ( n = 1) necessary electrical charge:

Takes you into the Faraday's laws an important role, its value is according to the current measurement accuracy:

(ie, with an estimated standard deviation of 0.0021 C · mol -1)

It is calculated from the Avogadro constant and the elementary charge:


The Faraday constant is often used in calculations of physics and chemistry, in particular the electrochemistry. It is a fixed quantity, so a natural constant. They will be used when conversion processes are associated with electric charges, such as electrolysis, for example, electroplating, or in fuel cells and batteries. Thus it is not only in science but also in the art of importance, especially in electroplating.

It is also used to calculate the molar change of the energy gain or lose one mole of electrons passing through a potential difference, and find practical application in the calculation of general reaction parameters such as the conversion of electrical potentials in free energy. A kJ / mol = 1000 ( eJ ) / ( NA e = F ) is about 0.01 eV.


The Faraday constant is named after Michael Faraday, whose fundamental work have allowed their first destination. Their determination was carried out for the first time in a galvanic deposition from the electric charge of the current flowed and the deposited amount of silver. 1 mol of silver ( molecular weight: MAg = 107.8682 g / mol) are separated by about 96,500 coulombs.

Simple derivation

It is the electrolysis of silver - on behalf of all substances with simple positively charged ion - viewed:

This formula is also true, if used instead of only one silver atom and only one electron per one mole of particles ( one mole of particles corresponds to about 6.022 · 1023 particles ):

To be able to deposit the amount of charge Q to a silver mole, determined by the elementary charge e of a single ion and the number of particles in a mole, the number of particles in a mole is expressed by the Avogadro constant NA.

Faraday's constant F = Q / n per mole of the charge amount Q (that is, for example, to deposit a silver mole ) thus obtained by:

For substances whose chemical valency z is different from the value 1, the charge is an appropriate multiple of the charge.


It is determined mostly by coulometric electrolysis, in which F can be calculated ( electrolysis time ) on the basis of Faraday's laws of mass, the molar mass, the charge Q and the time.

Modern coulometric measuring devices are in exactly the specified values ​​of the conventional 1990 Josephson constant KJ- 90 and the conventional 1990 von Klitzing constant RK -90

Calibrated. In such measurements are not the Faraday constant F, but based on the conventional Josephson 1990 and Klitzing constant Faraday constant F90 to be used in calculations. This is calculated from the Avogadro constant NA and the exact value of the conventional 1990 elementary charge e90 according to

And has - according to the 2010 CODATA recommendation for NA - the value: