In chemistry, the standard state of a material is its state at 1 standard atmosphere (101.325 kilopascals) and 25 degrees Celsius (298.15 kelvins). When the standard state is referred to in a chemical reaction, it also includes the condition that all solutions are at 1 mol/L or 1 mol/kg.
For a given material or substance, the standard state is the reference state for the material's thermodynamic state properties such as enthalpy, entropy, Gibbs free energy, and for a lot of other material standards.
See also : Standard temperature and pressure aka STP
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