In
chemistry
Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...
, the standard state of a material (pure
substance
Substance may refer to:
* Matter, anything that has mass and takes up space
Chemistry
* Chemical substance, a material with a definite chemical composition
* Drug substance
** Substance abuse, drug-related healthcare and social policy diagnosis ...
, mixture or
solution) is a reference point used to calculate its properties under different conditions. A superscript circle ° (degree symbol) or a
Plimsoll (⦵) character is used to designate a thermodynamic quantity in the standard state, such as change in
enthalpy (Δ''H''°), change in
entropy (Δ''S''°), or change in
Gibbs free energy (Δ''G''°).
The degree symbol has become widespread, although the Plimsoll is recommended in standards, see discussion about typesetting
below
Below may refer to:
*Earth
*Ground (disambiguation)
*Soil
*Floor
*Bottom (disambiguation)
Bottom may refer to:
Anatomy and sex
* Bottom (BDSM), the partner in a BDSM who takes the passive, receiving, or obedient role, to that of the top or ...
.
In principle, the choice of standard state is arbitrary, although the
International Union of Pure and Applied Chemistry (IUPAC) recommends a conventional set of standard states for general use.
The standard state should not be confused with
standard temperature and pressure
Standard temperature and pressure (STP) are standard sets of conditions for experimental measurements to be established to allow comparisons to be made between different sets of data. The most used standards are those of the International Union o ...
(STP) for gases, nor with the
standard solutions used in
analytical chemistry. STP is commonly used for calculations involving gases that approximate an
ideal gas, whereas standard state conditions are used for
thermodynamic calculations.
For a giv