Gas
Matter with no definite shape or volume.
Matter in a form that has low density, is easily compressible and expandable, and expands spontaneously when placed in a larger container. Molecules in a gas move freely and are relatively far apart.
Vapour often refers to a gas made of a substance that is usually encountered as a liquid or solid; for example, gaseous H2O is called water vapour.
See also: Boyles Gas Law, Charles Gas Law, Ideal Gas, Ideal Gas Law, Liquid, Noble Gases, Ratio of Specific Heats, Solid, Specific Gas Constant, Standard State, State of Matter.
Subjects: Chemistry Mechanical Engineering Physics