Faraday\'s laws of electrolysis

Michael Faraday, by Thomas Phillips c1841-1842

Faraday's laws of electrolysis are quantitative relationships based on the electrochemical researches published by Michael Faraday in 1834. Thomas Phillips ( October 18, 1770 - April 20, 1845) was an English portrait and subject painter. Michael Faraday, FRS ( September 22 1791 – August 25 1867) was an English ^[1]

1 Statements of the laws
2 Mathematical form
3 References
4 Further reading
5 See also

Statements of the laws

Several versions of the laws can be found in textbooks and the scientific literature. The most-common statements resemble the following:

Faraday's 1^st Law of Electrolysis - The mass of a substance altered at an electrode during electrolysis is directly proportional to the quantity of electricity transferred at that electrode. An electrode is an Electrical conductor used to make contact with a nonmetallic part of a circuit (e In chemistry and manufacturing electrolysis is a method of separating chemically bonded elements and compounds by passing an Electric current In Physics the term quantity of Electricity refers to the quantity of Electric charge. Quantity of electricity refers to electrical charge, typically measured in coulombs, and not to electrical current.

Faraday's 2^nd Law of Electrolysis - For a given quantity of electricity (electric charge), the mass of an elemental material altered at an electrode is directly proportional to the element's equivalent weight. Equivalent weight is the amount of an element that reacts or is involved in reaction with 1 mole of electrons The equivalent weight of a substance is its molar mass divided by an integer that depends on the reaction undergone by the material. Molar mass, symbol M, is the Mass of one mole of a substance ( Chemical element or Chemical compound)

Mathematical form

Faraday's laws can be summarised by

$m \ = \ ({ Q \over F })({ M \over z })$

where

m is the mass of the substance altered at an electrode

Q is the total electric charge passed through the substance

F = 96 485 C mol^-1 is the Faraday constant

M is the molar mass of the substance

z is the valence number of ions of the substance (electrons transferred per ion)

Note that M / z is the same as the equivalent weight of the substance altered. In Physics and Chemistry, the Faraday constant (named after Michael Faraday) is the magnitude of Electric charge per mole of An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge Equivalent weight is the amount of an element that reacts or is involved in reaction with 1 mole of electrons

For Faraday's first law, M, F, and z are constants, so that the larger the value of Q the larger m will be.

For Faraday's second law, Q, F, and z are constants, so that the larger the value of M / z (equivalent weight) the larger m will be.

In the simple case of constant-current electrolysis, $Q = I t$ leading to

$m \ = \ ({ I t\over F })({ M \over z })$

and then to

$n \ = \ ({ I t\over F })({ 1 \over z })$

where

n is the amount of substance ("number of moles") altered: n = m / M

t is the total time the constant current was applied. The amount of substance, n, of a sample or system is a Physical quantity which is proportional to the number of elementary entities present

In the more-complicated case of a variable electrical current, the total charge Q is the electric current I( $τ$ ) integrated over time $τ$ :

$Q = \int_0^t I(\tau) \ d \tau$

Here t is the total electrolysis time. Note that the parentheses in I( $τ$ ) do not indicate multiplication, but rather that the current is a function of time, $τ$ . ^[2]

References

^ Ehl, Rosemary Gene; Ihde, Aaron (1954). "Faraday's Electrochemical Laws and the Determination of Equivalent Weights". Journal of Chemical Education 31 (May): 226 – 232.
^ For a similar treatment, see Strong, F. C. (1961). "Faraday's Laws in One Equation". Journal of Chemical Education 38: 98.

Contents

Statements of the laws

Mathematical form

References

Further reading

See also