gassform

Gassform, or the gaseous form, is one of the fundamental states of matter characterized by the absence of a fixed shape and a fixed volume. Gases expand to fill the space available to them and are highly compressible. At the molecular level, gas particles move rapidly and interact weakly with one another, so gases typically have much lower density than liquids or solids. The term generally refers to the gaseous state of substances at a given temperature and pressure, in contrast with the term vapor, which denotes the gaseous phase of a substance that is normally liquid or solid at room temperature (for example, steam is the vapor of water).

The behavior of gases is commonly described by kinetic theory and, for many practical purposes, by the ideal gas law, PV = nRT, where P is pressure, V volume, n moles, R the gas constant, and T temperature. Real gases deviate from ideal behavior at high pressures or low temperatures, and equations of state such as the van der Waals equation provide corrections. At standard temperature and pressure, one mole of an ideal gas occupies about 22.4 liters.

Gases can form through phase transitions such as vaporization (liquid to gas) or sublimation (solid to gas). They can condense back to liquids or deposit as solids when cooled or compressed. Air, a mixture of nitrogen, oxygen, argon, carbon dioxide and other gases, is the most familiar example. The gas form is central to many applications, including chemical synthesis, combustion, environmental science, respiration, industrial gas production, and analytical techniques like gas chromatography.