State in which all concentrations are 1 M and all partial pressures are 1 MPa.
the state of the substance at 25°C and 1 atm; for solutions, standard state is 1 molar.
A reference state for thermodynamic measurements, defined for a liquid or solid as the pure substance at one atmosphere external pressure, for a gas as an ideal gas at one atmosphere pressure, and for a solution as a 1 M solution, in each case at the specified temperature
Standard state is depend from the melting and boiling points of the element. Elements must be in three state: gas, solid, or liquid.
a set of specific chemical conditions (for substances in solution, standard state is 1 concentration at 1 atm pressure and 250C) that create a reference point from which thermodynamic quantities can be d efined.
(° or ) 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.
the most stable state of a substance at 25 ºC and 1 bar (atmospheric pressure). For example, for O2 the standard state is (g), while for H2O it is (l), since these are the most stable states of these substances at room temperature conditions. Newer tables will probably list the substances at 1 bar, while older ones will likely use 1 atm. A bar is 100 kPa, and is so close to 1 atm, that the difference isn't very important when you are just learning about these concepts.
In chemistry, the standard state of a material is its state at 1 bar (100 kilopascals). This pressure of 1 bar was changed from 1 atm by IUPAC in http://www.iupac.org/goldbook/S05910.pdf 1990. The standard state of a material can be defined at any given temperature.
