chemistry guys
 

just wondering:
say you had a flask with some liquid in it, and you capped the flask but let a small opening. then if you heated the flask, allowed the liquid to boil and evaporate out of the flask, and then capped the flask and allowed it to cool, you almost create a vaccuum (assuming the glass was strong enough not to collapse in on itself) correct?
my question here is, would it be possible to create a complete vaccuum inside of the sealed flask, and if you did, what would the temperature be inside?

iirc:

from the heating, capping, and cooling, you do create lower air pressure. in addition, as long as your flask doesn't have any serious flaws, it can easily withstand a vacuum.

now - you could create a very close approximation to a vacuum by using a vacuum pump to remove nearly all of the air.

since temperature is really the measure of the state of excitement of atoms, since there aren't any atoms to measure i think the temperature would be considered absolute zero. however, it has been awhile since i took chemistry, so i may be wrong....

There are no perfect vacua. Your hole would allow air in as well as vapor out. You actually couldn't get it below atmospheric pressure this way. Putting in hot air at atmospheric pressure, and then capping and cooling would give you low pressure, but it isn't very good compared to a vacuum pump.

You can get enough of a vacuum to fill about 3/4 of a 2L flask by heating a small amount of water until it boils, then capping it with a stopper that has a hole in it, then inverting it and placing the stopper in a wide basin of water.

if you had a liquid in a flask, you could never approach a vacuum, because some of the liquids vapor would fill the emptiness in the air.

If you used a vacuum pump, however, and you were using some very robust vials, you could aproach a vacuum, and also have the temperature approach absolute zero, 0K, or -283C. You wouldnt be able to do this with your pyrex flask, it would definitely implode if the pressure got too low. The stopper probably wouldnt stay stopped either.

The same thing basically happens if you bring a drink on an airplane, to approximately the same degree as the boiling experiment.

Temperature is defined as the average kinetic energy of the atoms (or something like this) so if there were no matter there would be no temperature. Creating a perfect vacuum is practically impossible though.

A good example of a perfect vacuum on earth is in a barometer. The mercury is heavy enough that at the top of the glass cylinder a perfect vacuum forms.

As for the temperature, the vacuum has no temperature, (no molecules = no temp) however if you were to put an object in the vacuum (technically no longer a vacuum) say a thermometer, that thermometer would be heated by infra red radiation given off by all molecules that have heat. IR radiation can pass through a vacuum ( sun heats earth by IR) and strike an object, converting the IR radiation to the kinetic energy that moves molecules and is in turn: heat.

Your perfect vacuum is not perfect. There is a bit of mercury vapor for example that will always be there. Again, a perfect vacuum is not possible on macroscopic scales.

To say that the vacuum has no temperature depends on your definition of temperature. The usual one that people throw around is kinetic energy of molecules. This is however not precise. E=n/2kT for n degrees of freedom, but this depends on "degrees of freedom" meaning a very specific thing which doesn't always hold. In any case, that formula (and its inadequacies) come from a deeper definition. Its fairly involved, so I won't get into it. The basic idea, though, is that objects are said to be at the same temperature if they can be brought into contact with one another without heat (non-mechanical energy) flowing between them. So matt_mll's radiation would actually be said to be at a certain temperature even without matter being present. Its just semantics though.