Timeline for Why is there any vapor above the water surface at atmospheric pressure and room temperature?
Current License: CC BY-SA 4.0
20 events
| when toggle format | what | by | license | comment | |
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| Jan 2, 2020 at 19:15 | comment | added | Borun Chowdhury | @theorist the phase diagram was accidentally deleted. I restored it. | |
| Jan 2, 2020 at 17:32 | comment | added | hobbs | @BorunChowdhury well then... in that model, there is no air or any gas besides water. The scenarios in your question can't arise, and there are no interesting answers to give. | |
| Jan 1, 2020 at 19:26 | comment | added | theorist | @slebetman The phase diagrams are reality -- they are based on experimental measurement. You're obfuscating this by throwing out cliched philosophical statements. | |
| Jan 1, 2020 at 19:20 | comment | added | theorist | @aditya_stack No, the points on the phase diagram are equilibrium points. The phase diagram he showed (since deleted) tells you the phase of the system, at equilibrium, for a given T and p. | |
| Jan 1, 2020 at 11:19 | comment | added | Borun Chowdhury | @slebetman A generic statement like "all models are wrong and some are more wrong" are always correct and hence meaningless. The first step is to understand what a model even means before judging how right (or how wrong) it is vis-a-vis reality. | |
| Jan 1, 2020 at 11:11 | comment | added | Borun Chowdhury | @slebetman I am not (at this point) concerned with reality. I am trying to understand the predictions of the model. I will worry about matching reality after I have understood the model. | |
| Jan 1, 2020 at 9:15 | comment | added | slebetman | @aditya_stack - Not necessarily. To be honest I didn't read your explanation. I was just commenting on the OP's obsession on wishing reality fit a theory. Instead it is worth reminding ourselves that when model meets reality reality always wins and we must consider a different model to describe reality. Science does not explain, science only describes. If a description satisfies our curiosity our minds will take that description as an explanation | |
| Jan 1, 2020 at 6:30 | comment | added | aditya_stack | @slebetman So does that mean my explanation is wrong?? | |
| S Jan 1, 2020 at 2:46 | history | suggested | CJ Dennis | CC BY-SA 4.0 |
Improve spelling and formatting
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| Jan 1, 2020 at 0:43 | comment | added | Euro Micelli | “... enter the air if the air is not saturated with water vapor...”: more precisely, the energetic water molecule will enter the air anyway, regardless of saturation. It’s just that at 100% saturation, about the same number of (slower than average for vapor molecules) molecules in the air will be captured by the liquid surface, so no net molecule transfer occurs in either direction. | |
| Dec 31, 2019 at 23:56 | review | Suggested edits | |||
| S Jan 1, 2020 at 2:46 | |||||
| Dec 31, 2019 at 21:27 | comment | added | slebetman | @BorunChowdhury - Remember, all models (and this includes phase diagrams) are wrong but some are useful. Models are just that - they are not reality nor explanations of reality but simulations (models) of real-world phenomena. Phase diagrams just happens to be a good model for the behavior of bulk quantities of material but what happens at the surfaces/boundaries are not explained by the phase diagram. We had to create another model/theory to explain that phenomena and that is vapor pressure (which is also as wrong as phase diagrams but also useful) | |
| Dec 31, 2019 at 20:13 | comment | added | aditya_stack | @BorunChowdhury Conversely if temperature is kept constant, and we have (P,T) corresponding to liquid region, liquid will evaporate until the vapor pressure is equal to the external/atmospheric pressure. | |
| Dec 31, 2019 at 20:05 | comment | added | aditya_stack | @BorunChowdhury I think I get it now!! The points on the phase diagram do not necessarily represent steady state/ equilibrium points. For example, and let us look at PT diagrams, if we have some liquid with (P,T) corresponding to "liquid-only" region, and lets say the pressure is constant, then the liquid will evaporate until its temperature decreases to bring it to the equilibrium line. Points on the phase diagram not on the equilibrium lines will migrate towards the equilibrium lines. | |
| Dec 31, 2019 at 19:29 | comment | added | Borun Chowdhury | @aditya_stack That can't be correct. If you look at at T-V phase diagram (I'll add one to my question), you will see that on the left of the two-phase mixture you have only liquid. If what you are saying is correct, there would be no separate 2-phase mixture and all of the left side would be a 2-phase mixture. Also note that what you are saying is that no matter how much the external pressure, you cannot push all the vapor into the liquid whereas if you put a piston on a liquid+vapor system you can definitely push it all the way down to the liquid hence ensuring there is no vapor left. | |
| Dec 31, 2019 at 19:11 | comment | added | aditya_stack | @BorunChowdhury There is always a liquid-vapor equilibrium present at temp. below the critical temperature of gas. Note the definition of boiling point, which is the temperature at which vapor pressure of liquid equals atmospheric pressure. Vapor is always present at temperatures even below the boiling point | |
| Dec 31, 2019 at 16:39 | comment | added | Bob D | @BorunChowdhury See my update to my answer. | |
| Dec 31, 2019 at 16:38 | history | edited | Bob D | CC BY-SA 4.0 |
additional information
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| Dec 31, 2019 at 14:59 | comment | added | Borun Chowdhury | What do you make of the phase diagram of water in T-P space then? For example one found here researchgate.net/figure/…? At 1 ATM, below 100 C the pure water system is in a liquid phase. That means there is no vapor. "Can still exist" is not science. I am giving an argument as to why there should be no vapor. As for your evaporation comment, I agree there is evaporation and I am asking exactly how it happens at 50 C and 1 ATM and hence what the flaw in my reasoning is. | |
| Dec 31, 2019 at 14:30 | history | answered | Bob D | CC BY-SA 4.0 |