Faraday’s First Law of electrolysis: Mass
\(m\) of electrochemically-transformed substance is proportional to the charge
\(Q\) passed,
\(m\! \propto\! Q\).
Faraday’s Second Law of electrolysis: When the same electric charge (quantity of electricity)
\(Q\) is passed through several electrolytes, the mass
\(m_{\rm{i}}\) of the substances deposited are proportional to their respective chemical equivalent molar mass,
\(M_{\rm{i}}/z_{\rm{i}}\).
\[m_{1}/m_{2} = (M_{1}/z_{1})/(M_{2}/z_{2})\]
Notes: - The relationship may be formulated as \(m=MQ/zF\), where \(M\) is the molar mass of the substance, \(z\) the number of electrons transferred (see: electron number of an electrochemical reaction), and \(F\) is the Faraday constant.
- Measurement of charge using a coulometer relies on Faraday’s Law.
- If reference is made only to ‘Faraday’s Law of electrolysis’ the first law is meant.
Source:
PAC, 2020, 92, 641. 'Terminology of Electrochemical Methods of Analysis (IUPAC Recommendations 2019)' on page 653 (https://doi.org/10.1515/pac-2018-0109)