Editing Equation of state (section)

==Overview==
At present, there is no single equation of state that accurately predicts the properties of all substances under all conditions. An example of an equation of state correlates densities of gases and liquids to temperatures and pressures, known as the [[ideal gas law]], which is roughly accurate for weakly polar gases at low pressures and moderate temperatures. This equation becomes increasingly inaccurate at higher pressures and lower temperatures, and fails to predict condensation from a gas to a liquid.

The general form of an equation of state may be written as
<math display="block">f(p, V, T) = 0</math>

where <math>p</math> is the pressure, <math>V</math> the volume, and <math>T</math> the temperature of the system. Yet also other variables may be used in that form. It is directly related to [[Phase rule|Gibbs phase rule]], that is, the number of independent variables depends on the number of substances and phases in the system.

An equation used to model this relationship is called an equation of state. In most cases this model will comprise some empirical parameters that are usually adjusted to measurement data. Equations of state can also describe solids, including the transition of solids from one crystalline state to another. Equations of state are also used for the modeling of the state of matter in the interior of stars, including [[neutron star]]s, dense matter ([[quark–gluon plasma]]s) and radiation fields. A related concept is the [[perfect fluid]] [[equation of state (cosmology)|equation of state used in cosmology]].

Equations of state are applied in many fields such as [[process engineering]] and petroleum industry as well as pharmaceutical industry.

Any consistent set of units may be used, although [[International System of Units|SI]] units are preferred. [[Thermodynamic temperature|Absolute temperature]] refers to the use of the [[Kelvin]] (K), with zero being absolute zero.

*<math>n</math>, number of [[mole (unit)|moles]] of a substance
*<math>V_m</math>, <math>\frac{V}{n}</math>, [[molar volume]], the volume of 1 mole of gas or liquid
*<math>R</math>, [[gas constant|ideal gas constant]] ≈ 8.3144621{{nbsp}}J/mol·K
*<math>p_c</math>, pressure at the critical point
*<math>V_c</math>, molar volume at the critical point
*<math>T_c</math>, absolute temperature at the critical point