Faraday constant
Template:Short description Template: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:Nowrap it is expressed in units of coulombs per mole (C/mol). As such, it represents the "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">Template:Cite book</ref> 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):
DerivationEdit
The Faraday constant can be thought of as the conversion factor between the mole (used in chemistry) and the coulomb (used in physics and in practical electrical measurements), and is therefore of particular use in electrochemistry. Because there are exactly NA = Template:Val entities per mole,<ref name="SI2019" /> and there are exactly Template:Math elementary charges per coulomb,<ref name="SI2019" /> the Faraday constant is given by the quotient of these two quantities:
One common use of the Faraday constant is in electrolysis calculations. One can divide the amount of charge (the current integrated over time) by the Faraday constant in order to find the chemical amount of a substance (in moles) that has been electrolyzed.
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.<ref>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">Template:Cite journal</ref>
Other common unitsEdit
- 96.485 kJ per volt–gram-equivalent
- 23.061 kcal per volt–gram-equivalent
- 26.801 A·h/mol
Faraday – a unit of chargeEdit
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>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 charges (or of negative one mole of electrons), that is,
- 1 faraday = F × 1 mol = Template:Val.
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 (Template:Nowrap).
See alsoEdit
- Farad, the unit of electrical capacitance
- Faraday efficiency
- Faraday's laws of electrolysis
- Faraday cup
ReferencesEdit
Template:Scientists whose names are used in physical constants Template:Michael Faraday Template:Mole concepts