Why Solids and Pure Liquids are not Part of Equilibrium Expression
Why Solids and Pure Liquids are not Part of Equilibrium Expression

Summary/Abstract: The article deals with the expression of equilibrium constant of a reaction that might include a solid or a pure liquid as a reactant or a product. The typical textbook explanation for excluding terms relating to solids and pure liquid is that their concentrations are constant and so need not be included. This need would not arise if the equilibrium constant were written in terms of activities rather than concentrations or pressures, but the concept of activities is not covered that early in a typical undergraduate syllabus. In this article the concept of Gibbs energy is used to explain why the equilibrium constant is written as it is.

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