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This article was the subject of a Wiki Education Foundation-supported course assignment, between 22 January 2021 and 29 April 2021. Further details are available
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Above undated message substituted from Template:Dashboard.wikiedu.org assignment by PrimeBOT ( talk) 20:59, 16 January 2022 (UTC)
This article is wrong when it says evaporation is when liquid becomes gasous without being heated to boiling point. I'll fix it-- 124.186.101.229 08:42, 14 November 2007 (UTC)
Ouch. My students happened to find this article and now I have to fight the confusion and misconceptions it has caused. This article is dead wrong when it says: "When a molecule near the surface absorbs enough energy to overcome the vapor pressure, it will escape and enter the surrounding air as a gas." That is not how it works. Firstly, vapour pressure is neither a force nor an energy. Temperature in gases is (see kinetic gas theory) an indirect measure of the average velocity of the molecules and similar (but more complicated) arguments can be made for liquids. When you increase the temperature you increase the average velocity, shifting the entire velocity distribution to higher values. What this means is that when you increase the temperature, you increase the fraction of molecules that have a kinetic energy that is large enough to escape from the liquid and go into gas phase. This is the reason why the vapour pressure increases when the temperature increases. Note: this process keeps happening even when the partial pressure of the substance has increased such that it equals the vapour pressure. (The article calls this "saturated" and says that no evaporation happens then). What is true, at steady-state at least, is that there is no net evaporation. Evaporation and condensation are two processes that happen simultaneously. I'm unfortunately not an expert in physical chemistry, but I have read a few research articles on estimating volatility from physical characteristics and the actual process, on a molecular level, is (at least from my perspective) rather complicated. I would suggest the following change: To escape from the liquid to the gas phase, a molecule must have enough kinetic energy to escape the intermolecular forces within the liquid. In a liquid of a certain temperature, the individual molecules have different kinetic energy and, to simplify, the temperarture is a measure of the average kinetic energy. When the temperature increases, this distribution shifts towards higher kinetic energy and the fraction of molecules with high enough kinetic energy to escape the liquid increases. This is why the vapour pressure increases with increasing temperature. At steady-state the partial pressure of the substance in the gas phase above the liquid equals the vapour pressure and the net evaporation rate is zero (i.e. the evaporation rate equals the condensation rate) I would suggest that someone with a solid knowledge of physical chemistry look up proper references. (It might be noted that the partial pressure close to a liquid surface often can be assumed to equal the vapour pressure and that the rate of evaporation will be determined by the film thickness, i.e. how thick the film is where the concentration, n_A/V=P_A/RT changes, see e.g. Stefan diffusion… Saittam ( talk) 11:29, 17 December 2020 (UTC)
Has anyone ever fixed "evaporation is when liquid becomes gaseous without being heated to boiling point"? Apparently not. I'll fix it. Dan Hickman ( talk) 23:55, 11 December 2007 (UTC) what is the answer then? What is evaporation? "Evaporation is a spontaneous process in which liquid when kept open in atmosphere, gets converted into it's vapour at a temperature below it's boiling point".
As evaporation is an endothermic process, it brings about coolness. However, to understand endothermic nature of evaporation, we must understand, "the changes taking place at molecular level" during the process of evaporation.
Understanding concept of evaporation & it's consequences, taking example of water:
In liquid state, molecules of water are joined with each other through a weak chemical bond called, "Hydrogen bond". This weak force, resulted through hydrogen bonding, holds the molecule of water together and retards them escaping into the surrounding. Further, in liquid state, the molecules of water are always in random motion called, "Brownian motion", which imparts some kinetic energy to each molecule of water. However, due to continuous inter moleular collision taking place among the molecules of water, some of them are moving very fast while some very slow. Due to this reason each of them does not posses same amount of kinetic energy. It is due to this reason that a more realistic scientific term, "average kinetic energy" is used for this. At any temperature, there always exists a fraction of molecules of water possesing sufficiently high kinetic energy to escape into surrounding by breaking some of the hydrogen bonds. This fraction of molecules of water, which continuously escape into the surrounding, is called, "evaporation"! At lower temperature, fraction of such molecules of water possesing sufficiently high kinetic energy is small, causing slow evaporation; but at higher temperature, fraction of such molecules becomes large, causing speedy evaporation. Here, the important point is, "energy is needed to maintain the fraction water molecules undergoing evaporation". As this energy is continuously absorbed from the surrounding, the surrounding becomes cooler. — Preceding unsigned comment added by Chemiyog ( talk • contribs) 07:57, 8 October 2014 (UTC)
Water evaporation is a special case, but an important one. In still air, over still water, a saturated vapor layer would develop immediately above the water. But humid air is less dense than dry air, so this vapor layer would be buoyant and drive convection. An important detail to understand in the case would be, does diffusion or convection dominate in determining the long-term evaporation rate of the water? - 69.87.199.175 ( talk) 15:08, 28 February 2008 (UTC)
I suggest that the article has a section on the special case of water evaporation in air, linked to psychrometrics which doesn't seem to cover evaporation or condensation in detail. This would clarify that the rest of the article was about evaporation in general, so future edits can confine water evaporation to this section and general principles to the rest. Natty Stott ( talk) 20:38, 20 November 2013 (UTC)
"On average, the molecules do not have enough energy to escape from the liquid, or else the liquid would turn into vapor quickly." -- this is stupid Needs to be rephrased, as in various cases the liquid does turn into vapor more or less "quickly". -- Writtenonsand ( talk) 16:03, 24 July 2008 (UTC)
"On average, only a fraction of the molecules in a liquid have enough heat energy to escape from the liquid." isn't much better. What does "on average" mean? S C Cheese ( talk) 16:35, 15 May 2021 (UTC)
Re: "Three key parts to evaporation are heat, humidity and air movement." 1) Humidity is a key part of the (important) evaporation of water but not of evaporation in general? 2) Surface area is a key part to evaporation? Bill B —Preceding unsigned comment added by 216.69.46.3 ( talk) 20:33, 8 September 2008 (UTC)
Why has somebody replaced humidity with atmospheric pressure here? Did they mean the vapour pressure of water in the air? In general is evaporation mainly influenced by the partial pressure of the gas evaporating or does the presence of other gas significantly slow it down? Natty Stott ( talk) 17:35, 16 November 2013 (UTC)
Link is gone! DGerman ( talk) 00:20, 31 July 2012 (UTC)
this article needs to explain why, after running a dishwasher, plastic or tupperware dishes are commonly still wet long after smooth glass or china dishes are dry. —Preceding unsigned comment added by 70.131.106.2 ( talk) 00:34, 30 June 2010 (UTC)
Remember - heat is the driving force for evaporation. The glass (silica is involved) can "absorb" alot more heat and then evaporate the moisture "quicker" than the other materials mentioned. Dok Uranium ( talk) 05:13, 27 March 2011 (UTC)
Isn't viscosity of the liquid a factor whereby there is less evaporation from more viscous liquids? - perhaps more so than density? Is there an expert who can advise on this? Eeno11 ( talk) 15:14, 6 September 2011 (UTC)
No it doesn't, at least in a simple picture. Do you have an example in mind? Density doesn't have any effect either. So, some work needed... AlanParkerFrance ( talk) 10:45, 13 November 2012 (UTC)
June 19, 2019 - I removed this from the Factors affecting rate section: ";Concentration of other substances in the air: If the air is already saturated with other substances, it can have a lower capacity for the substance evaporating. citation needed" Carax ( talk) 00:14, 20 June 2019 (UTC)
We need an engineer to work on this. I can supply some input from having worked with evaporators in the pulp and paper industry, but I don't really have time to do it now. Also I need someone to check my work. Thanks. Phmoreno ( talk) 20:50, 29 April 2013 (UTC)
Is the article's account of evaporative cooling complete? Certainly the statistical account, that the vapor molecules leaving the liquid are the faster ones, must be part of the explanation. But for it to be the whole explanation, the average translational energy of the departing molecules would have to equal that of the air into which they escape. (The vibrational and rotational energy need not be the same since water vapor is triatomic and bent while oxygen and nitrogen are only diatomic, but that only makes the cooling effect even greater.) This seems highly unlikely, even for air well below 0 °C.
More likely, surely, is that on entry to air the molecules are initially well below average in translational energy and are speeded up to average by collision with the other air molecules, and moreover additional rotational and vibrational energy is absorbed. This will reduce the temperature of the skin layer of air, and then it's a good question how that cooling effect on the skin layer is divided between the liquid below and the air above.
Is this in fact the case, and if so is there a source for it? If there is it should go in the article. If not it sounds like a nice little project for a physics student to investigate, especially the question of how the skin layer cooling is apportioned between liquid and air, presumably as a function of the temperatures of the respective phases. Vaughan Pratt ( talk) 18:43, 28 October 2013 (UTC)
Meanwhile I found some relevant discussion at Talk:Evaporative_cooler#Physical_principles_section_needs_work. Although agreeing with the above it doesn't offer any usable sources (the BEC link suggested there is not ideal since this is not about Bose-Einstein condensates). Vaughan Pratt ( talk) 20:16, 28 October 2013 (UTC)
It seems to me that this article could have been edited less arrogantly and destructively. Is it necessary to say, "This article is wrong", or, "this is stupid"?
Due to the way this Talk page was edited, I'm not sure who asked, "what is the answer then?", or whether the question was ever answered. However, the fact that the question was asked after two people said they would "fix it", suggests destructive editing.
Hopefully, obsolete explanations will not be included in the, "wrong", and, "stupid" categories; they are history, and should be included in the History section. Ideally, a History section about a chemistry subject would go back at least as far as Alchemy, and perhaps back to ancient applications of the subject. In the case of Evaporation that would probably include early stills and porous ice trays and jugs such as ancient Egyptians and others used to chill water, and Mesoamerican descendants continue to use. Downstrike ( talk) 13:33, 15 November 2013 (UTC)
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in "Factors influencing the rate of evaporation" the "Concentration of other substances in the air" should not have effect, the correct factor should be "Concentration of other substances in the liquid". 139.78.154.131 ( talk) 18:34, 24 February 2016 (UTC)
I take back the thing about "Concentration of other substances in the air" should be deleted. However, "Concentration of other substances in the liquid" should be added into the factors. The whole reference and explanation could be found in wiki page "Colligative properties" — Preceding unsigned comment added by 139.78.252.129 ( talk) 18:30, 25 February 2016 (UTC)
The final sentence of the lead seems to me to be a bit odd. "The tracking of evaporation from its source on the surface of the earth, through the atmosphere as vapor or clouds, and to its fate as precipitation closes the atmospheric water cycle, and embodies the concept of the precipitationshed."
First off, it's a bit of an awkward sentence to make sense of.
Second, and more important - why is precipicationshed there? It's a bit of a niche concept, and consensus on Talk:Precipitationshed seems to be that it's not really a word. Why is it even mentioned in the lead paragraph of the article on evaporation?
I think this sentence could be tidied up grammatically, and should drop the mention of the precipitationshed (while perhaps retaining reference to the water cycle). Girth Summit ( talk) 07:08, 31 October 2016 (UTC)
I've gone ahead and removed this sentence. I thought about rewording it to make it a bit more readable, while keeping the essence of its description of the rest of the water cycle; however, it occurs to me that this is an article about evaporation, and so probably does not need the rest of the water cycle to be described - there is a link to that water cycle at the start of the paragraph. Girth Summit ( talk) 03:12, 5 November 2016 (UTC)
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223.235.143.135 ( talk) 08:59, 12 June 2020 (UTC) vipul kumar shah
Oxidation state 102.143.9.200 ( talk) 04:01, 5 April 2022 (UTC)