Faraday constant

Faraday constant
source
Name	Faraday constant
Value	96485.33212(40) C mol^−1
Units	coulomb per mole
Quantity	electric charge per mole of electrons
Related	Avogadro constant; elementary charge; mole

Faraday constant The Faraday constant quantifies the total electric charge carried by one mole of elementary charges (electrons) and is used throughout electrochemistry, physical chemistry, and metrology. It links the microscopic charge carried by an electron to macroscopic amounts described by the mole and features in laws and equations across electrolysis, galvanic cells, and standardization efforts by bodies such as the International Bureau of Weights and Measures.

Definition and value

The Faraday constant is defined as the product of the Avogadro constant and the elementary charge, giving the total coulombs per mole of electrons; its currently accepted value reflects international determinations by the International Committee for Weights and Measures and the CODATA. Numerically F ≈ 96485.33212 C mol^−1, with uncertainty determined through precision experiments at institutions like the National Institute of Standards and Technology and the Physikalisch-Technische Bundesanstalt. This value is used alongside the Boltzmann constant and the Planck constant in fundamental metrology.

Historical background

The constant is named after Michael Faraday, whose 19th-century experiments on electrolysis and electromagnetism established quantitative relations between charge and chemical change; contemporaries and successors such as John Frederic Daniell and Humphry Davy applied these relations to cell chemistry. Nineteenth-century standardization efforts involved organizations including the Royal Society and later international coordination through the Metre Convention. Developments in atomic theory by figures like Amedeo Avogadro and experimental advances by laboratories associated with Anders Ångström and J. J. Thomson informed the linkage between atomic charge and macroscopic charge that the constant embodies.

Physical significance and derivation

Physically, F connects the discrete charge of a single electron to the macroscopic quantity of charge in one mole of particles via F = NA·e, where NA is the Avogadro constant and e is the elementary charge. It therefore appears in electrochemical forms of the Nernst equation and the Butler–Volmer equation describing electrode kinetics, and in formulations of the Faraday's laws of electrolysis (named after Michael Faraday). The constant allows conversion between amounts of substance (moles) as used in stoichiometry and electric charge as used in electrical circuits described by laws from Georg Ohm and James Clerk Maxwell.

Measurement methods

Experimental determination of F historically combined measurements of the Avogadro constant via crystallographic methods applied to silicon spheres by collaborations involving the International Avogadro Project and determinations of the elementary charge via methods rooted in the Millikan oil drop experiment replication and modern single-electron tunneling devices developed in laboratories such as those at the National Physical Laboratory (United Kingdom). Electrochemical measurements include coulometric titration and the use of the hydrogen volt standard in cells related to the Josephson effect and the quantum Hall effect realized at places like the National Institute of Standards and Technology and the Physikalisch-Technische Bundesanstalt, linking electrical standards from Brian Josephson and Klaus von Klitzing to determinations of F.

Applications and uses

The Faraday constant is central to quantitative electrochemistry, appearing in calculations for electrodeposition, corrosion rates, and battery capacity assessments for technologies developed by companies and research centers in the energy sector. It is used in analytical techniques such as coulometry employed by chemical firms and laboratories associated with the American Chemical Society and in industrial electroplating facilities. F also features in theoretical work on redox reactions in environmental studies and biochemical processes investigated by researchers affiliated with universities like Harvard University and University of Cambridge, and in standards for electrical metrology upheld by institutions tied to the International System of Units.

Relationship to other constants

F is directly related to the Avogadro constant and the elementary charge through multiplication. It enters equations alongside the Faraday laws of electrolysis and interrelates with the gas constant when converting between molar quantities in thermochemical contexts investigated by scientists such as Jules-Émile Verschaffelt. In metrology, F is used with the Planck constant and the Josephson constant when realizing electrical units from quantum standards developed by researchers including Brian Josephson and Klaus von Klitzing.

Category:Physical constants