Coulomb
Definition and meaning of Coulomb in chemistry.
Coulomb (symbol C) is the SI unit of electric charge, defined as the quantity of charge transported by a constant current of one ampere flowing for one second (1 C = 1 A·s). It is central to quantifying charge transfer in electrochemical processes.
In more detail
Because charge equals current multiplied by time (Q = I × t), the coulomb links directly to Faraday's laws of electrolysis, which relate the amount of substance produced or consumed at an electrode to the total charge passed. One mole of electrons carries a charge of about 96,485 C, a quantity known as the Faraday constant (F). Chemists use coulombs to calculate the mass of metal deposited in electroplating, the gas volume liberated in electrolysis, or the number of electrons transferred in a redox reaction, via Q = nFz, where n is moles of substance and z is the number of electrons per formula unit.
Key facts
| Field | Physical Chemistry |
|---|---|
| Symbol | C |
| SI definition | 1 C = 1 A · s |
| Elementary charge | 1 e = 1.602 × 10⁻¹⁹ C |
Passing a steady current of 2.00 A through molten NaCl for 500 seconds transfers Q = 2.00 A × 500 s = 1000 C of charge, which corresponds to 1000 C ÷ 96,485 C/mol ≈ 0.01036 mol of electrons, enough to deposit about 0.01036 mol of Na metal at the cathode.
Frequently asked questions
How does the coulomb relate to the Faraday constant?
The Faraday constant (F ≈ 96,485 C/mol) is the charge carried by one mole of electrons; it converts moles of electrons transferred in a redox or electrolysis reaction into coulombs, and vice versa.
Who was the coulomb named after?
It is named after Charles-Augustin de Coulomb, the 18th-century French physicist who formulated Coulomb's law describing the electrostatic force between charged particles.