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gas,in physics, one of the three commonly recognized states of matter, the other two being solid and liquid. A substance in the gaseous state has neither definite shape nor definite volume. Like liquids, gases are fluids and assume the shape of their containers. Unlike liquids, they will expand to fill any container, regardless of its size. All gases condense into liquids or solids when sufficiently cooled or compressed (see compressioncompression,
external stress applied to an object or substance, tending to cause a decrease in volume (see pressure). Gases can be compressed easily, solids and liquids to a very small degree if at all.
..... Click the link for more information. ; condensationcondensation,
in physics, change of a substance from the gaseous (vapor) to the liquid state (see states of matter). Condensation is the reverse of vaporization, or change from liquid to gas.
..... Click the link for more information. ; liquefactionliquefaction,
change of a substance from the solid or the gaseous state to the liquid state. Since the different states of matter correspond to different amounts of energy of the molecules making up the substance, energy in the form of heat must either be supplied to a substance
..... Click the link for more information. ). Most gases first liquefy, but some pass directly into the solid state (see sublimationsublimation
, change of a solid substance directly to a vapor without first passing through the liquid state. The term is also used to describe the reverse process of the gas changing directly to the solid again upon cooling.
..... Click the link for more information. ); carbon dioxide, for example, can condense into dry ice. Some gases are extremely soluble in certain liquids, the liquid absorbing many times its own volume of gas. Some solids, by a process called adsorption, can take up many times their own volume of certain gases. The behavior of gases under various conditions of pressure, temperature, and volume is described by the various gas lawsgas laws,
physical laws describing the behavior of a gas under various conditions of pressure, volume, and temperature. Experimental results indicate that all real gases behave in approximately the same manner, having their volume reduced by about the same proportion of the
..... Click the link for more information. . Many of the properties of gases can be understood by considering the fact that only a small part of the volume of a gas is occupied by its atoms or molecules, which are in rapid, random motion. See kinetic-molecular theory of gaseskinetic-molecular theory of gases,
physical theory that explains the behavior of gases on the basis of the following assumptions: (1) Any gas is composed of a very large number of very tiny particles called molecules; (2) The molecules are very far apart compared to their sizes,
..... Click the link for more information. .
A state of matter, including natural gas and propane, used as a fuel to produce energy, generally for lighting and heating.
To expose to a war gas.
A phase of matter in which the substance expands readily to fill any containing vessel; characterized by relatively low density.
1. a substance in a physical state in which it does not resist change of shape and will expand indefinitely to fill any container. If very high pressure is applied a gas may become liquid or solid, otherwise its density tends towards that of the condensed phase
2. any substance that is gaseous at room temperature and atmospheric pressure
3. any gaseous substance that is above its critical temperature and therefore not liquefiable by pressure alone
a. a fossil fuel in the form of a gas, used as a source of domestic and industrial heat
b. (as modifier): a gas cooker
5. a gaseous anaesthetic, such as nitrous oxide
7. US an informal name for flatus