Faraday's laws of electrolysis are quantitative relationships based on the electrochemical research published by Michael Faraday in 1833.
Michael Faraday reported that the mass() of elements deposited at an electrode in g is directly proportional to the Charge() in Coulombs.
Here, the constant of proportionality is called the Electro-Chemical Equivalent(e.c.e) of the substance. Thus, the e.c.e. can be defined as the mass of the substance deposited/liberated per unit charge.
Faraday discovered that when the same amountequivalent weight (). This turns out to be the molar mass() divided by the valence()
is passed through different electrolytes/elements connected in series, the mass of the substance liberated/deposited at the electrodes in g is directly proportional to their chemical equivalent/
- (From 1st Law)
A monovalent ion requires 1 electron for discharge, a divalent ion requires 2 electrons for discharge and so on. Thus, if electrons flow, atoms are discharged.
So the mass discharged
(where is Avogadros number)
(From Q = xe)
Faraday's laws can be summarized by
where is the molar mass of the substance (in grams per mol) and is the valency of the ions .
For Faraday's first law, , , and are constants, so that the larger the value of the larger m will be.
For Faraday's second law, , , and are constants, so that the larger the value of (equivalent weight) the larger m will be.
In the simple case of constant-current electrolysis, leading to
and then to
- n is the amount of substance ("number of moles") liberated: n = m/M
- t is the total time the constant current was applied.
For the case of an alloy whose constituents have different valencies, we have
where wi represents the mass fraction of the ith element.
In the more complicated case of a variable electric current, the total charge Q is the electric current I() integrated over time :
Here t is the total electrolysis time.
This section needs expansion
with: Real-life application/worked out eg. of Faraday's Laws. You can help by adding to it. (August 2020)