Faraday constant
{{Short description|Physical constant: Electric charge of one mole of electrons}}
{{distinguish|farad}}
{{Infobox physical quantity
| name = Faraday constant
| othernames =
| width =
| background =
| image = Michael_Faraday_(1791-1867).jpg
| caption = Michael Faraday, the constant's namesake
| unit = coulomb per mole (C/mol)
| otherunits =
| symbols = {{math|F}}
| baseunits = s⋅A⋅mol−1
| dimension = wikidata
| extensive =
| intensive =
| conserved =
| transformsas =
| derivations = {{math|1=F = eNA}}
| value = {{val|96,485.3321233100184 | u=C/mol}}
}}
In physical chemistry, the Faraday constant (symbol {{math|F}}, sometimes stylized as ℱ) is a physical constant defined as the quotient of the total electric charge ({{math|q}}) by the amount ({{math|n}}) of elementary charge carriers in any given sample of matter: {{nowrap|{{math|F}} {{=}} {{math|q/n}};}} it is expressed in units of coulombs per mole (C/mol).
As such, it represents the "molar elementary charge", that is, the electric charge of one mole of elementary carriers (e.g., protons). It is named after the English scientist Michael Faraday. Since the 2019 revision of the SI,{{Cite book |last=Newell |first=David B. |url=https://www.nist.gov/si-redefinition/meet-constants |title=The International System of Units (SI) |last2=Tiesinga |first2=Eite |publisher=National Institute of Standards and Technology |year=2019 |series=NIST Special Publication 330 |location=Gaithersburg, Maryland |doi=10.6028/nist.sp.330-2019 |doi-access=free |s2cid=242934226}} the Faraday constant has an exactly defined value, the product of the elementary charge ({{math|e}}, in coulombs) and the Avogadro constant ({{math|NA}}, in reciprocal moles):
: {{math|1=F = e × NA = {{val|9.64853321233100184|e=4|u=C/mol}}.}}
Derivation
The Faraday constant can be thought of as the proportionality factor between the charge in coulombs (used in physics and in practical electrical measurements) and the amount of substance in moles (used in chemistry), and is therefore of particular use in electrochemistry, particularly in electrolysis calculations. Because the elementary charge is exactly {{Physical constants|e|symbol=no|ref=no}}, and there are exactly {{Physical constants|NA|symbol=yes|unit=no|ref=no}} entities per mole, the Faraday constant is given by the product of these two quantities:
: {{math|1=F = e × NA}}
: {{math|1= = {{val|1.602176634|e=-19|u=C}} × {{val|6.02214076|e=23|u=mol-1}}}}
: {{math|1= = {{val|9.64853321233100184|e=4|u=C/mol}}.}}
The value of {{math|F}} was first determined in the 1800s 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.[http://physics.nist.gov/cuu/Constants/historical1.html NIST Introduction to physical constants] Until about 1970, the most reliable value of the Faraday constant was determined by a related method of electro-dissolving silver metal in perchloric acid.{{Cite journal |last=IUPAC |author-link=International Union of Pure and Applied Chemistry |year=1976 |title=Status of the Faraday constant as an analytical standard |journal=Pure and Applied Chemistry |volume=45 |issue=2 |pages=125–130 |doi=10.1351/pac197645020125 |doi-access=free}}
Other common units
- 96.485 kJ per volt–gram-equivalent
- 23.061 kcal per volt–gram-equivalent
- 26.801 A·h/mol
Faraday – a unit of charge
Related to the Faraday constant is the "faraday", a unit of electrical charge. Its use is much less common than of the coulomb, but is sometimes used in electrochemistry.[https://books.google.com/books?id=r-Qpy0KQayIC&pg=PA51 Foundations of Physics, Volume 2, by R. S. Gambhir, 1993, p. 51] One faraday of charge is the charge of one mole of elementary charges (or of negative one mole of electrons), that is,
: 1 faraday = F × 1 mol = {{Val|9.64853321233100184E4|u=C}} = {{Val|6.02214076E23|u=e}}.
Conversely, the Faraday constant F equals 1 faraday per mole.
The faraday is not to be confused with the farad, an unrelated unit of capacitance ({{nowrap|1=1 farad = 1 coulomb / 1 volt}}).
See also
References
{{reflist}}
{{Scientists whose names are used in physical constants}}
{{Michael Faraday}}
{{Mole concepts}}
Category:Electrochemical concepts