(Redirected from Faraday's law of electrolysis)

Faraday's laws of electrolysis are quantitative relationships based on the electrochemical researches published by Michael Faraday in 1834.[1] In the same years, in Italy, Carlo Matteucci discovered the laws of electrolysis by a method totally independent Faraday's methods. The laws of electrolysis can also be called Faraday-Matteucci's laws.

## Mathematical form

Faraday's laws can be summarized by

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

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, ${\displaystyle Q=It}$ leading to

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

and then to

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

where:

• n is the amount of substance ("number of moles") liberated: n = m/M
• t is the total time the constant current was applied.

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

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

Here t is the total electrolysis time.[2]