Faraday constant: Difference between revisions
imported>CATion1248 Added Category: Molar quantities |
imported>JGHFunRun It is probably worth noting explicitly that N_0 is unitless since it's also a bit rare |
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| transformsas = | | transformsas = | ||
| derivations = {{math|1=''F'' = ''eN''<sub>A</sub>}} | | derivations = {{math|1=''F'' = ''eN''<sub>A</sub>}} | ||
| value = {{val|96,485.3321233100184 | u=C | | 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 of substance|amount]] ({{math|''n''}}) of [[elementary charge carrier]]s in any given sample of matter: {{nowrap|{{math|''F''}} {{=}} {{math|''q''/''n''}};}} it is expressed in [[unit of measurement|units]] of [[coulomb]]s per [[mole (unit)|mole]] (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 of substance|amount]] ({{math|''n''}}) of [[elementary charge carrier]]s in any given sample of matter: {{nowrap|{{math|''F''}} {{=}} {{math|''q''/''n''}};}} it is expressed in [[unit of measurement|units]] of [[coulomb]]s per [[mole (unit)|mole]] (C/mol). | ||
As such, it represents the "[[molar quantity|molar]] [[elementary charge]]",<ref name="SI2019" /> 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]],<ref name="SI2019">{{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}}</ref> the Faraday constant has an exactly defined value, the product of the elementary charge ({{math|''e''}}, in coulombs) and the [[Avogadro constant]] ({{math|''N''<sub>A</sub>}}, in reciprocal moles): | As such, it represents the "[[molar quantity|molar]] [[elementary charge]]",<ref name="SI2019" /> 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]],<ref name="SI2019">{{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}}</ref> the Faraday constant has an exactly defined value, the product of the elementary charge ({{math|''e''}}, in coulombs) and the [[Avogadro constant]] ({{math|''N''<sub>A</sub>}}, in reciprocal moles): | ||
: {{math|1=''F'' = ''e'' × ''N''<sub>A</sub> = {{val|9.64853321233100184|e=4|u=C/mol}}.}} | |||
== Derivation == | |||
The Faraday constant can be thought of as the [[Proportionality (mathematics)|proportionality factor]] between the charge in [[coulomb|coulombs]] (used in physics and in practical electrical measurements) and the [[amount of substance]] in [[Mole (unit)|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}},<ref name="SI2019" /> and there are exactly {{Physical constants|NA|symbol=yes|unit=no|ref=no}} entities per mole,<ref name="SI2019" /> the Faraday constant is given by the product of these two quantities: | |||
: {{math|1=''F'' = ''e'' × ''N''<sub>A</sub>}} | : {{math|1=''F'' = ''e'' × ''N''<sub>A</sub>}} | ||
: {{math|1=  = {{val|1.602176634|e=-19|u=C}} × {{val|6.02214076|e=23|u=mol-1}}}} | : {{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 | : {{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 (electricity)|current]] was passed for a measured time, and using [[Faraday's law of electrolysis]].<ref>[http://physics.nist.gov/cuu/Constants/historical1.html NIST Introduction to physical constants]</ref> 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]].<ref name="IUPAC">{{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}}</ref> | 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 (electricity)|current]] was passed for a measured time, and using [[Faraday's law of electrolysis]].<ref>[http://physics.nist.gov/cuu/Constants/historical1.html NIST Introduction to physical constants]</ref> 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]].<ref name="IUPAC">{{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}}</ref> | ||
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== Faraday – a unit of charge == | == 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.<ref>[https://books.google.com/books?id=r-Qpy0KQayIC&pg=PA51 ''Foundations of Physics, Volume 2'', by R. S. Gambhir, 1993, p. 51]</ref> One faraday of charge is the charge of one mole of [[elementary charge]]s (or of negative one mole of electrons), that is, | 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.<ref>[https://books.google.com/books?id=r-Qpy0KQayIC&pg=PA51 ''Foundations of Physics, Volume 2'', by R. S. Gambhir, 1993, p. 51]</ref> One faraday of charge is the charge of one [[Mole (unit)|mole]] of [[elementary charge]]s (or of negative one mole of electrons), that is, | ||
: 1 faraday = ''F'' × 1 mol = {{ | : 1 faraday = ''F'' × 1 mol = {{Val|9.64853321233100184E4|u=C}} = ''N''<sub>0</sub> × ''e'' = {{Val|6.02214076E23|u=''e''}}. | ||
Conversely, the Faraday constant ''F'' equals 1 faraday per mole. | Where ''N''<sub>0</sub> is [[Avogadro's number]], the unitless counterpart to ''N''<sub>A</sub>. 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}}). | The faraday is not to be confused with the [[farad]], an unrelated unit of [[capacitance]] ({{nowrap|1=1 farad = 1 coulomb / 1 volt}}). | ||
Latest revision as of 22:54, 17 November 2025
Template:Short description Script error: No such module "Distinguish". Template:Infobox physical quantity In physical chemistry, the Faraday constant (symbol Template:Math, sometimes stylized as ℱ) is a physical constant defined as the quotient of the total electric charge (Template:Math) by the amount (Template:Math) of elementary charge carriers in any given sample of matter: Template:Math = Template:Math; it is expressed in units of coulombs per mole (C/mol). As such, it represents the "molar elementary charge",[1] 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,[1] the Faraday constant has an exactly defined value, the product of the elementary charge (Template:Math, in coulombs) and the Avogadro constant (Template:Math, in reciprocal moles):
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 Template:Physical constants,[1] and there are exactly Template:Physical constants entities per mole,[1] the Faraday constant is given by the product of these two quantities:
The value of Template:Math 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.[2] 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.[3]
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.[4] 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 = Template:Val = N0 × e = Template:Val.
Where N0 is Avogadro's number, the unitless counterpart to NA. 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 (1 farad = 1 coulomb / 1 volt).
See also
- Farad, the unit of electrical capacitance
- Faraday efficiency
- Faraday's laws of electrolysis
- Faraday cup
References
Template:Scientists whose names are used in physical constants Template:Michael Faraday Template:Mole concepts
- ↑ a b c d Script error: No such module "citation/CS1".
- ↑ NIST Introduction to physical constants
- ↑ Script error: No such module "Citation/CS1".
- ↑ Foundations of Physics, Volume 2, by R. S. Gambhir, 1993, p. 51