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I have read the definition of vapour on Wikipediabut I don't seem to have a clear idea about the difference between a vapour and a gas. I know what it means when it says, "gas at a temperature lower than its critical temperature".
In this graph, the blue curve, means the part where gaseous and liquid phase coexist, so did the scientists coined the term Vapour for only this reason so, that we can have orderly fashion of different states of matter? My question is Are we naming vapour and gas to the same thing just at different temperature or they are distinct in some other read more too? Are there some other things which justify that vapour and gas are actually different things than just a gas below and above critical temperature? Vapor is a much older word alluding to dampness and it was not coined by scientists. It is in use since the s.
The actual meaning of meaning of vapor is " Matter in the whaat of a steamy or imperceptible exhalation; esp. This is the original 13th century meaning of vapor. The German equivalent of vapor is Dampf which is relatively clearer in terms of feeling- imagine entering a basement which is damp from water vapor. Gas is relatively a new word as per the unabridged Oxford English Dictionary, and it entered English in the s.
In fact, the OED mentions the distinction " Gas: A substance in a state in which it expands freely to fill the whole of a container, having no fixed shape unlike a solid and source fixed volume unlike a liquid ; spec. A substance which is a liquid at room temperature or under ambient conditions, and if it is heated enough so that the liquid evaporates same root of wordyou can call that as vapor of that substance. Examples: Mercury is a liquid metal, when it is heated enough in a an electric bulb, it becomes a gas, hence the name mercury vapor lamp.
It is not called a mercury gas lamp. It is not necessary that heat be involved.
You will find here usage "cold vapor method for Hg analysis" again for mercury which means that Hg was a liquid in a sample but by blowing a gas over it, it has been evaporated. The recent meaning of vapor from OED, "Vapor: In modern scientific use, a fluid that fills a space like a gas but, being below its critical temperature, can be liquefied by pressure alone. This is clear enough. Now apply this distinction to your phase diagram and notice the position of the critical point.
The vapor "state" is below the critical point. At normal lab conditions there is a fairly obvious distinction between things that could exist as liquids and things where no liquid phase is possible. Oxygen, for example, is a permanent gas, but dichloromethane is not.]