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]
NA ≈ 6.022141×1023 mol−1.[4]

NA is the Avogadro constant (the ratio of the number of particles 'N' to the amount of substance 'n' - a unit mole), 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, NA, and e.

Contents

Other Common Units of Faraday's Constant

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

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