Faraday constant

In physics and chemistry, the Faraday constant (named after Michael Faraday) is the magnitude of electric charge per mole of electrons.^[1] It has the currently accepted value

F = 96,485.3365(21) C/mol.^[2]

The constant F has a simple relation to two other physical constants:

$F\,=\,eN_{A}$

where:

e ≈ 1.6021766×10⁻¹⁹ C;^[3]

N_A ≈ 6.022141×10²³ mol⁻¹.^[4]

N_A is the Avogadro constant, and e is the elementary charge or the magnitude of the charge of an electron. This relation is true 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.

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.

Other Common Units of Faraday's Constant

• 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. 96,485.3365(21) 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.

See also

• Farad, unit of capacitance
• Michael Faraday
• Faraday cage
• Faraday efficiency
• Faraday's law of electrolysis
• Faraday's law of Electromagnetic induction

References

1. ^ 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.
2. ^ ^{a b} "CODATA Value: Faraday constant". The NIST Reference on Constants, Units, and Uncertainty. US National Institute of Standards and Technology. June 2011. http://physics.nist.gov/cgi-bin/cuu/Value?f. Retrieved 2011-06-23. 
3. ^ "CODATA Value: elementary charge". The NIST Reference on Constants, Units, and Uncertainty. US National Institute of Standards and Technology. June 2011. http://physics.nist.gov/cgi-bin/cuu/Value?e. Retrieved 2011-06-23. 
4. ^ "CODATA Value: Avogadro constant". The NIST Reference on Constants, Units, and Uncertainty. US National Institute of Standards and Technology. June 2011. http://physics.nist.gov/cgi-bin/cuu/Value?na. Retrieved 2011-06-23. 
5. ^ NIST Introduction to physical constants
6. ^ Foundations Of Physics, Volume 2, by R. S. Gambhir, p51