User:Milton Beychok/Sandbox

The Columbia Encyclopedia, Sixth Edition | Date: 2008

There is fundamentally no difference between the terms gas and vapor, but gas is used commonly to describe a substance that appears in the gaseous state under standard conditions of pressure and temperature, and vapor to describe the gaseous state of a substance that appears ordinarily as a liquid or solid. (under Vaporization)

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Water vapor is the most important greenhouse gas

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When a substance turns changes from a solid or liquid into a gas, the process is called vaporization. The material is said to vaporize or evaporate. Heat of vaporization. Vapor pressure.

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here is no significant physical or chemical difference between a vapor and a gas. This is the most important point. However, the words have slightly different connotations. Remember that these are just connotations. There is sometimes considerable overlap between the terms, so precise distinctions are not necessary and probably not even possible.Any vapor could technically be called a gas, although in many situations this would sound weird or awkward. One way in which a gas can earn the “vapor” appellation is when the gaseous phase is in equilibrium with the corresponding liquid or solid. We call the pressure of the gas phase in equilibrium with the corresponding liquid phase "Vapor pressure". A liquid that changes phase to a gas is said to " vaporize" rather than to "gasify".

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The boiling point of a liquid may also be defined as the temperature at which it changes its state from a liquid to a gas, but we refer to that phase change as "vaporization".

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The term vapor is sometimes used in a more extended sense, as identical with gas; and the difference between the two is not so much one of kind as of degree, the latter being applied to all permanently elastic fluids except atmospheric air, the former to those elastic fluids which lose that condition at ordinary temperatures.

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Vapor is the gaseous form of a liquid. Vapor describes the gaseous state of a substance..

The meaning of gas or vapor

There is no significant physical or chemical difference between a gas and a vapor. However, in common usage, there are somewhat different connotations. There is often considerable overlap between the two terms and their connotations, so precise distinctions are not necessary and probably not even possible.