Term: equilibrium constant
https://doi.org/10.1351/goldbook.E02177

Definition:
Quantity characterizing the equilibrium of a chemical reaction and defined by an expression of the type Kx = ΠB.xB(νB), where νB is the stoichiometric number of a reactant (negative) or product (positive) for the reaction and x stands for a quantity which can be the equilibrium value either of pressure, fugacity, amount concentration, amount fraction, molality, relative activity or reciprocal absolute activity defining the pressure based, fugacity based, concentration based, amount fraction based, molality based, relative activity based or standard equilibrium constant (then denoted K°), respectively.

Related Terms:
1) stoichiometric number (http://doi.org/10.1351/goldbook.S06025).
2) amount concentration (http://doi.org/10.1351/goldbook.A00295).
3) relative activity (http://doi.org/10.1351/goldbook.R05256).
4) absolute activity (http://doi.org/10.1351/goldbook.A00019).
5) standard equilibrium constant (http://doi.org/10.1351/goldbook.S05915).

Source: Green Book, 2nd ed., p. 50 (https://goldbook.iupac.org/files/pdf/green_book_2ed.pdf)

Citation: 'equilibrium constant' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.E02177

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