Talk:Vapor

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yeow, are we having fun yet? Frobnitzem 13:35, 7 June 2007 (UTC)

Yeah, I think so. Anyway, I've got a couple of thoughts: First, the terms "fog" and "mist" are used as examples of "vapor". But in fact, fog and mist are both examples of matter (in this case water) in its liquid state, as fine droplets. They may be suggestive of the coincident presence of vapor, but in themselves aren't examples of vapors. Unlike fog and mist, the vapor phase, being a gas, is invisible (at least for water). Second, the claim is made that the term "vapor" is only correct when in equilibrium with a liquid or solid phase. Yet the usage "water vapor" is common even among scientists to refer to that fraction of air which consists of water in its gaseous state, even when not in the presence of, or equilibrium with, any liquid water at all. The presumably correct term "water gas" is never heard. I suspect that this may have historical reasons stemming from the archaic use of the term "water gas" to refer to the element hydrogen, but there is also the use of the term "mercury vapor", even in situations where there is no liquid phase present. Are these just sloppy usage of the term? I suspect not. Any thoughts on whether changes are needed in the text? Or am I being too pedantic? Jeepien 18:05, 13 September 2007 (UTC)

I have now corrected the definition so that it does not depend on having a liquid present. I have also included Hg vapor as an example, and specified that fog and mist are liquid droplets. Only a year late! Dirac66 (talk) 19:32, 10 October 2008 (UTC)

Anomalous behaviour of water

In the figure caption:

"The dotted green line gives the anomalous behaviour of water"

What is this referring to? It's a curve on the temperature-pressure axes. If it's referring to expansion of ice as it cools from 0 to -4°C, what does that mean in terms of pressure? — Preceding unsigned comment added by 125.253.44.20 (talk) 10:28, 30 September 2013 (UTC)

Most substances at temperatures below their triple points will only undergo a single phase transition (from gas to solid) if the pressure is slowly increased from zero (i.e. vacuum) to infinity. On a phase diagram this is represented by curves (phase boundaries) that only go from left to right. Water, however, can undergo three phase changes provided that it is within a narrow temperature range just below its triple point. Take a look at the following water phase diagram:

https://en.wikipedia.org/wiki/Phase_diagram#/media/File:Phase_diagram_of_water.svg

If you draw a vertical straight line at a temperature just below the triple point, you can see that as pressure increases water will sublime from vapour to solid, then melt back into a liquid, and finally condense into solid again. This anomalous property of water produces a solid-liquid phase boundary that goes from right to left and then left to right, resulting in a "S" shaped curve.202.73.1.98 (talk) 08:31, 11 November 2015 (UTC)

Vapor as liquid droplets

Most examples of vapour used in common parlance are actually aerosols. Mist, Fog and Water Vapour over a kettle are all liquid water. I'm planning on adding to the lead a sentence about this disparity in usage. Sources I'm considering (will add more as I find) Oxford Dictionary A substance diffused or suspended in the air, especially one normally liquid or solid: dense clouds of smoke and toxic vapour SPACKlick (talk) 19:27, 13 April 2015 (UTC)

Also no free link but OED has for steam 6. a. The vapour into which water is converted when heated. In popular language, applied to the visible vapour which floats in the air in the form of a white cloud or mist, and which consists of minute globules or vesicles of liquid water suspended in a mixture of gaseous water and air. (Also sometimes applied to the vapour arising from other liquids when heated.) In modern scientific and technical language, applied only to water in the form of an invisible gas. The invisible ‘steam’, in the modern scientific sense, is, when its temperature is lowered, converted into the white vapour called ‘steam’ in popular language, and this under continued cooling, becomes ‘water’ in the liquid form. dry steam, in Steam-engine working, steam containing no suspended vesicles of water: opposed to wet steam.

So essentially there is a large difference between the scientific definition of "water vapour" and the layman definition of "water vapour". I recommend creating a new section regarding the dual definitions, or at least a paragraph in the introduction.202.73.1.98 (talk) 08:40, 11 November 2015 (UTC)

I agree with this person. There should be two completely different definitions given here. If the strict scientific definition of vapor is being used, the pictures of aerosols should be taken down. Amulekii (talk) 05:05, 10 March 2017 (UTC)

A bug detected

on the main photo link to "equilibrium" redirects to page of "nitrogen dioxide" i suggest fixing this bug

Mist is not vapor, vapor is invisible

For fog, cloud, steam and mist formation either water is aerosolized from liquid or vapor is condensed on seed particles at a low temperature. Last edit is misleading since mechanism isn't fully explained and might cause people to think mist and vapor is the same thing. Vapournotgas (talk) 13:03, 6 May 2021 (UTC)