![]() At high pressures, the volume of a real gas is often considerably larger than that of an ideal gas. It also fails for most heavy gases, such as many refrigerants, and for gases with strong intermolecular forces, notably water vapor. The ideal gas model tends to fail at lower temperatures or higher pressures, when intermolecular forces and molecular size becomes important. 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) at standard temperature and pressure (a temperature of 273.15 K and an absolute pressure of exactly 10 5 Pa). Generally, a gas behaves more like an ideal gas at higher temperature and lower pressure, 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. 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 over a considerable parameter range around standard temperature and pressure. 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. The requirement of zero interaction can often be relaxed if, for example, the interaction is perfectly elastic or regarded as point-like collisions. 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. An ideal gas is a theoretical gas composed of many randomly moving point particles that are not subject to interparticle interactions.
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