Standard State

A set of conditions defined to allow convenient comparison of thermodynamic properties.

The standard state for a gas is the the state of the pure substance in the gaseous phase at the standard pressure, with the gas behaving ideally.

The standard state for liquids and solids is the state of the most stable form of the substance at the standard pressure.

Temperature is not included in the definition of standard state and must be specified, but when not given a temperature of 25°C is usually implied.

See also: Gas, Liquid, Solid.