gas

gas State of matter in which molecules are free to move in any direction; a gas spreads by diffusion. Any quantity of gas will occupy its entire container. Because of their low densities, most gases are poor conductors of heat and electricity (although at high voltages a gas may be ionized and become electrically conductive). When cooled, gases become liquids. Some, such as carbon dioxide, can be liquefied by pressure alone. All gases follow certain laws, such as Avogadro's law, Boyle's law, Charles' law, Graham's law, and the ideal gas laws. All involve volume and pressure, with Graham's law particularly concerned with diffusion. See also plasma; solid