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Evaporation through vacuum

by aochider
Tags: evaporation, vacuum
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aochider
#19
Mar23-14, 01:02 PM
P: 13
Quote Quote by dauto View Post
You don't need zero K to test it. The heat absorbed during evaporation can be measured.
i think there might be a misunderstanding. my question is regarding if it is possible to change a liquid into a gas even if there were 0 heat in the substance trying to be evaporated. it seems like it is not though, based on the responses in this thread.
nasu
#20
Mar23-14, 03:33 PM
P: 1,970
Quote Quote by aochider View Post
i think there might be a misunderstanding. my question is regarding if it is possible to change a liquid into a gas even if there were 0 heat in the substance trying to be evaporated. it seems like it is not though, based on the responses in this thread.
Yes, it may be. The part in bold does not make much sense.
The heat cannot be in a substance. By the definition of heat.
The substance may have thermal energy. And this thermal energy may be changed by transferring heat to or from the substance. Even at zero K the thermal energy does not have to be zero.

But is this relevant to your question about evaporation and vacuum?
The heat involved in evaporation can be measured at any temperature.
At very low temperature most (or almost all) of the substances are solid anyway. So your problem regarding evaporation of liquid is not in this range of temperatures.
Evaporation is a well known and studied phenomenon. What is the problem, after all?
aochider
#21
Mar23-14, 03:56 PM
P: 13
ah, thanks for the explanation. i had been using heat and thermal energy interchangeably. i also didnt realize something could have any thermal energy at absolute zero.

Quote Quote by nasu View Post
At very low temperature most (or almost all) of the substances are solid anyway. So your problem regarding evaporation of liquid is not in this range of temperatures.
Evaporation is a well known and studied phenomenon. What is the problem, after all?
usually evaporation is taught as having a pressure and temperature component. that is why im asking if something can evaporate *solely* based on the pressure component. so yes, most substances might be a solid at absolute zero, but that is not what im asking about. im asking if evaporation could be induced by only pressure, in the complete absence of thermal energy.

im not trying to challenge what we know about evaporation but trying to understand its limits better.
nasu
#22
Mar23-14, 04:40 PM
P: 1,970
Quote Quote by aochider View Post

usually evaporation is taught as having a pressure and temperature component. that is why im asking if something can evaporate *solely* based on the pressure component. so yes, most substances might be a solid at absolute zero, but that is not what im asking about. im asking if evaporation could be induced by only pressure, in the complete absence of thermal energy.

im not trying to challenge what we know about evaporation but trying to understand its limits better.
This (bold) is a vague and imprecise statement which is encountered often in business and politics statements. I don't think it helps understanding.
Evaporation is a phenomenon. It does not have temperature or pressure as "components".
We may say that both temperature and pressure (of the atmosphere above liquid) determine the rate of evaporation, for example. Or that vapor pressure depends on temperature.

Evaporation is not "induced" by parameters (temperature, pressure) but by thermal motion of the molecules in the liquid. By a phenomenon, not by a parameter.
Then it become obvious that without thermal motion there will be no evaporation. All molecules will be frozen, at rest. So no evaporation. Vacuum or not.

But this is a hypothetical situation.

Of course, the molecules may have some motion which is not the thermal motion but it induced by external fields. This may induce (or facilitate) the molecules breaking free from the liquid.
aochider
#23
Mar23-14, 04:48 PM
P: 13
Quote Quote by nasu View Post
This (bold) is a vague and imprecise statement which is encounter often in business and politics statements. I don't think it helps understanding.
Evaporation is a phenomenon. It does not have temperature or pressure as "components".
We may say that both temperature and pressure (of the atmosphere above liquid) determine the rate of evaporation, for example. Or that vapor pressure depends on temperature.

Evaporation is not "induced" by parameters (temperature, pressure) but by thermal motion of the molecules in the liquid. By a phenomenon, not by a parameter.
Then it become obvious that without thermal motion there will be no evaporation. All molecules will be frozen, at rest. So no evaporation. Vacuum or not.

But this is a hypothetical situation.

Of course, the molecules may have some motion which is not the thermal motion but it induced by external fields. This may induce (or facilitate) the molecules breaking free from the liquid.
that is exactly what i needed to know. thanks!!!


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