Faraday's laws of electrolysis

Michael Faraday.

Faraday's laws of electrolysis are quantitative relationships based on the electrochemical researches published by Michael Faraday in 1834.^[1]

Mathematical form

Faraday's laws can be summarized by

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

where:

m is the mass of the substance liberated at an electrode in grams
Q is the total electric charge passed through the substance in coulombs
F = 96485 C mol⁻¹ is the Faraday constant
M is the molar mass of the substance in grams per mol
z is the valency 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.

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, $Q=It$ leading to

m\ =\ \left({It \over F}\right)\left({M \over z}\right)

and then to

n\ =\ \left({It \over F}\right)\left({1 \over z}\right)

where:

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

Q=\int _{0}^{t}I(\tau )\ d\tau

Here t is the total electrolysis time.^[2]

↑ Ehl, Rosemary Gene; Ihde, Aaron (1954). "Faraday's Electrochemical Laws and the Determination of Equivalent Weights". Journal of Chemical Education. 31 (May): 226–232. Bibcode:1954JChEd..31..226E. doi:10.1021/ed031p226.
↑ For a similar treatment, see Strong, F. C. (1961). "Faraday's Laws in One Equation". Journal of Chemical Education. 38 (2): 98. Bibcode:1961JChEd..38...98S. doi:10.1021/ed038p98.

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