Standard state Guide, Meaning , Facts, Information and Description
In chemistry, the standard state of a material is its state at 1 standard atmosphere (101 325 pascals) and 25 degrees Celsius (298.15 kelvin). When the standard state is referred to in a chemical reaction, it also includes the condition that all solutions are at 1 M.The standard state is the reference state for enthalpy and a lot of material standards.
See also : Standard temperature and pressure aka STP