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An ideal gas is a theoretical gas composed of many randomly moving point particles that are not subject to interparticle interactions.[1] The ideal gas concept is useful because it obeys the ideal gas law, a simplified equation of state, and is amenable to analysis under statistical mechanics. The requirement of zero interaction can often be relaxed if, for example, the interaction is perfectly elastic or regarded as point-like collisions.
Under various conditions of temperature and pressure, many real gases behave qualitatively like an ideal gas where the gas molecules (or atoms for monatomic gas) play the role of the ideal particles. Many gases such as nitrogen, oxygen, hydrogen, noble gases, some heavier gases like carbon dioxide and mixtures such as air, can be treated as ideal gases within reasonable tolerances[2] over a considerable parameter range around standard temperature and pressure. Generally, a gas behaves more like an ideal gas at higher temperature and lower pressure,[2] as the potential energy due to intermolecular forces becomes less significant compared with the particles' kinetic energy, and the size of the molecules becomes less significant compared to the empty space between them. One mole of an ideal gas has a volume of 22.710 954 64... litres (exact value based on 2019 redefinition of the SI base units)[3] at standard temperature and pressure (a temperature of 273.15 K and an absolute pressure of exactly 105 Pa).[note 1]
The ideal gas model tends to fail at lower temperatures or higher pressures, when intermolecular forces and molecular size becomes important. It also fails for most heavy gases, such as many refrigerants,[2] and for gases with strong intermolecular forces, notably water vapor. At high pressures, the volume of a real gas is often considerably larger than that of an ideal gas. At low temperatures, the pressure of a real gas is often considerably less than that of an ideal gas. At some point of low temperature and high pressure, real gases undergo a phase transition, such as to a liquid or a solid. The model of an ideal gas, however, does not describe or allow phase transitions. These must be modeled by more complex equations of state. The deviation from the ideal gas behavior can be described by a dimensionless quantity, the compressibility factor, Z.
The ideal gas model has been explored in both the Newtonian dynamics (as in "kinetic theory") and in quantum mechanics (as a "gas in a box"). The ideal gas model has also been used to model the behavior of electrons in a metal (in the Drude model and the free electron model), and it is one of the most important models in statistical mechanics.
If the pressure of an ideal gas is reduced in a throttling process the temperature of the gas does not change. (If the pressure of a real gas is reduced in a throttling process, its temperature either falls or rises, depending on whether its Joule–Thomson coefficient is positive or negative.)
^Tuckerman, Mark E. (2010). Statistical Mechanics: Theory and Molecular Simulation (1st ed.). p. 87. ISBN 978-0-19-852526-4.
^ abcCengel, Yunus A.; Boles, Michael A. (2001). Thermodynamics: An Engineering Approach (4th ed.). McGraw-Hill. p. 89. ISBN 0-07-238332-1.
^"CODATA Value: molar volume of ideal gas (273.15 K, 100 kPa)". Retrieved 2023-09-01.
^"CODATA Value: molar volume of ideal gas (273.15 K, 101.325 kPa)". Retrieved 2017-02-07.
^Calvert, J. G. (1990). "Glossary of atmospheric chemistry terms (Recommendations 1990)". Pure and Applied Chemistry. 62 (11): 2167–2219. doi:10.1351/pac199062112167.
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An idealgas is a theoretical gas composed of many randomly moving point particles that are not subject to interparticle interactions. The idealgas concept...
The idealgas law, also called the general gas equation, is the equation of state of a hypothetical idealgas. It is a good approximation of the behavior...
The molar gas constant (also known as the gas constant, universal gas constant, or idealgas constant) is denoted by the symbol R or R. It is the molar...
these properties expressed by the ideal gas law (see § Ideal and perfect gas section below). Gas particles are widely separated from one another, and consequently...
temperature in gases. This theory also explains the idealgas law and the observed heat capacity of monatomic (or 'noble') gases. The idealgas law is based...
Δ T = 0 {\displaystyle \Delta T=0} d T = 0 {\displaystyle dT=0} For idealgases only, internal energy Δ U = 0 {\displaystyle \Delta U=0} while in adiabatic...
The volume occupied by an idealgas at a constant temperature is directly proportional to the number of molecules of the gas present in the container....
also applies to metals in the Fermi gas approximation. Degenerate matter is usually modelled as an ideal Fermi gas, an ensemble of non-interacting fermions...
1085 °C). When pressure approaches zero, all real gas will behave like idealgas, that is, pV of a mole of gas relying only on temperature. Therefore, we can...
expansion is an isothermal process for an idealgas. Adiabatic compression occurs when the pressure of a gas is increased by work done on it by its surroundings...
speed of sound is how fast vibrations travel. The speed of sound in an idealgas depends only on its temperature and composition. The speed has a weak...
are pumps, gas compressors, turbines, nozzles, and diffusers. Most steady-flow devices operate under adiabatic conditions, and the ideal process for...
perfect gas models are idealgas models in the sense that they all follow the idealgas equation of state. However, the idea of a perfect gas model is...
appear as a straight horizontal line. If an idealgas is used in an isochoric process, and the quantity of gas stays constant, then the increase in energy...
densities of gases and liquids to temperatures and pressures, known as the idealgas law, which is roughly accurate for weakly polar gases at low pressures...
the set of distinct states of a system, besides the special case of an idealgas. This topic was investigated to completion by Josiah Willard Gibbs who...
the opposite to "pressure". In an idealgas, molecules have no volume and do not interact. According to the idealgas law, pressure varies linearly with...
expansion factor and is denoted by γ (gamma) for an idealgas or κ (kappa), the isentropic exponent for a real gas. The symbol γ is used by aerospace and chemical...
ensemble of idealgas particles, in which he defined entropy as proportional to the natural logarithm of the number of microstates such a gas could occupy...
single spring. For example, it predicts that every atom in a monatomic idealgas has an average kinetic energy of 3/2kBT in thermal equilibrium, where...
or molecules of the gas. The basic version of the model describes an idealgas. It treats the collisions as perfectly elastic and as the only interaction...
kelvin) and energy (with unit joule). Macroscopically, the idealgas law states that, for an idealgas, the product of pressure p and volume V is proportional...
_{i}^{0}}=M_{i}v_{i}} For idealgases, the molar volume is given by the idealgas equation; this is a good approximation for many common gases at standard temperature...
molar heat capacity of the gas; c V {\displaystyle c_{V}} is constant for an idealgas. The internal energy of any gas (ideal or not) may be written as...
{\displaystyle n=+\infty } for an isochoric process. In addition, when the idealgas law applies: n = 1 {\displaystyle n=1} for an isothermal process, n =...