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Faraday constant
In physics and chemistry, the Faraday constant, denoted by the symbol F and named after Michael Faraday, is the magnitude of electric charge per mole of electrons.[1] It has the currently accepted value
9.64853399(24) x 104 C mol−1.
The constant F has a simple relation to two other physical constants:
\( F\,=\,eN_{A} \)
where
- e ≈ 1.6021766×10−19 C;[2]
- NA ≈ 6.022141×1023 mol−1.[3]
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.
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.[4] Research is continuing into more accurate ways of determining the interrelated constants F, NA, and e.
Other common units of faraday's constant
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.[5] One faraday of charge is the magnitude of the charge of one mole of electrons, i.e. 96485.3365(21) C.[6]
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 says to Smithers, "give him Faraday's Constant." The check is written for $96,485.34.
See also
Faraday cage
Faraday efficiency
Faraday's law of electrolysis
Faraday's law of Electromagnetic induction
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.
"CODATA Value: elementary charge". The NIST Reference on Constants, Units, and Uncertainty. US National Institute of Standards and Technology. June 2011. Retrieved 2011-06-23.
"CODATA Value: Avogadro constant". The NIST Reference on Constants, Units, and Uncertainty. US National Institute of Standards and Technology. June 2011. Retrieved 2011-06-23.
NIST Introduction to physical constants
Foundations Of Physics, Volume 2, by R. S. Gambhir, p51
"CODATA Value: Faraday constant". The NIST Reference on Constants, Units, and Uncertainty. US National Institute of Standards and Technology. June 2011. Retrieved 2011-06-23.
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