Faraday constant
The Faraday constant, denoted by the symbol F and sometimes stylized as ℱ, is named after Michael Faraday. In physics and chemistry, this constant represents the magnitude of electric charge per mole of electrons.[1] It has the currently accepted value
- F = 96485.33212... C mol^{−1}.[2]
This constant has a simple relation to two other physical constants:
where
N_{A} is the Avogadro constant (the ratio of the number of particles, N, which is unitless, to the amount of substance, n, in units of moles), and e is the elementary charge or the magnitude of the charge of an electron. This relation holds because the amount of charge of a mole of electrons is equal to the amount of charge in one electron multiplied by the number of electrons in a mole.
One common use of the Faraday constant is electrolysis. One can divide the amount of charge in coulombs by the Faraday constant in order to find the amount (in moles) of the element that has been oxidized.
The value of F was first determined by weighing the amount of silver deposited in an electrochemical reaction in which a measured current was passed for a measured time, and using Faraday's law of electrolysis.[5] Research is continuing into more accurate ways of determining the interrelated constants F, N_{A}, and e.
2019 redefinition
Since the 2019 redefinition of SI base units, which introduced exactly defined values for the elementary charge and the Avogadro constant, the Faraday constant is exactly 1.602176634×10^{−19} C × 6.02214076×10^{23} mol^{−1} = 96485.3321233100184 C/mol.
Other common units
- 96 485 J (96.485 kJ) per volt gram equivalent
- 23.061 kcal per volt gram equivalent
- 26.801 A·h/mol
Faraday unit of charge
Related to Faraday's constant is the "faraday", a unit of electrical charge. It is much less common than the coulomb, but sometimes used in electrochemistry.[6] One faraday of charge is the magnitude of the charge of one mole of electrons, i.e. 96485.33212... C.[2]
Expressed in faradays, the Faraday constant F equals "1 faraday of charge per mole".
This faraday unit is not to be confused with the farad, an unrelated unit of capacitance (1 farad = 1 coulomb / 1 volt).
Popular media
The Simpsons episode "Dark Knight Court" (RABF10) has Mr. Burns asking Comic Book Guy how much he wants for his entire comic book inventory. He says "the speed of light expressed as dollars" and Mr. Burns tells Smithers to "just give him Faraday's Constant". The check is written for $96,485.34.
See also
References
- The term "magnitude" is used in the sense of "absolute value": The charge of an electron is negative, but F is always defined to be positive.
- "2018 CODATA Value: Faraday constant". The NIST Reference on Constants, Units, and Uncertainty. NIST. 20 May 2019. Retrieved 2019-05-20.
- "2018 CODATA Value: elementary charge". The NIST Reference on Constants, Units, and Uncertainty. NIST. 20 May 2019. Retrieved 2019-05-20.
- "2018 CODATA Value: Avogadro constant". The NIST Reference on Constants, Units, and Uncertainty. NIST. 20 May 2019. Retrieved 2019-05-20.
- NIST Introduction to physical constants
- Foundations Of Physics, Volume 2, by R. S. Gambhir, 1993, p. 51