Faraday's Laws of Electrolysis
Definition and meaning of Faraday's Laws of Electrolysis in chemistry.
Faraday's laws of electrolysis state that the mass of a substance produced or consumed at an electrode is directly proportional to the quantity of electric charge passed through the electrolyte (first law), and that for a fixed charge, the masses of different substances liberated are proportional to their equivalent weights, molar mass divided by the number of electrons transferred (second law).
In more detail
Formulated by Michael Faraday in 1834, the two laws combine into a single equation: m = QM/(nF), where Q = It is the charge in coulombs, M is molar mass, n is the number of electrons transferred per ion, and F is the Faraday constant, 96,485 coulombs per mole of electrons. The laws showed that electric charge and matter interact in fixed, quantized proportions, evidence later used to support the existence of the electron. They are still used to calculate current efficiency and deposit thickness in electroplating, electrorefining, and industrial electrolysis such as aluminum and chlor-alkali production.
Key facts
| Faraday constant (F) | 96,485 C/mol |
|---|---|
| Governing equation | m = QM/(nF) |
| Established | 1834, by Michael Faraday |
| Field | Physical Chemistry |
Passing a steady current of 2.00 A for 965 seconds through molten CuCl2 delivers Q = It = 1930 C. At the cathode, Cu2+ + 2e- -> Cu, so n = 2, and m = QM/(nF) = (1930 x 63.55)/(2 x 96,485) = 0.636 g of copper deposited.
Frequently asked questions
What is the Faraday constant?
It is the electric charge carried by one mole of electrons, F = 96,485 C/mol, equal to Avogadro's number times the elementary charge on an electron.
How do the first and second laws differ?
The first law relates the mass of one substance to the charge passed; the second law compares different substances electrolyzed by the same charge, showing their deposited masses are proportional to molar mass divided by ionic charge (n).