### Temperature in a vacuum

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I have questiong about the temperature in a vacuum. According to the answer given in my recitation, when a mole of liquid water goes to a mole of water vapor in a vacuum it is at 273K. However, if it is a vacuum then why is there a temperature? If it is a true vacuum, then the temperature should be 0K because otherwise there are molecules in the space since temperature is just the average kinetic energy of the molecules. Am I not understanding this concept correctly?

-- Anonymous, February 15, 2000

What about the water molecules in the vacuum?

-- Anonymous, February 16, 2000

I think you may be confused. 0 kelvin is absolute zero, it's theoritical and has yet to be reached in real life. The temperature of a vacuum is 0 degrees celsuis, which is freezing and also 273 Kelvin.

-- Anonymous, February 16, 2000

Interestingly enough, a study partner and myself were discussing issues involving vacuums, although from a different angle. Anyhow, if there are water molecules in the container, then by default it is not a vacuum, right? If a vacuum is defined as a system under which pressure = 0, then there cannot be any water molecules (or any for that matter) in that system because if there were then there would be things to bounce around the container thus producing the macroscopic phenomenon of pressure. Also, since temperature is dependent on there being particles having kinetic energy, if there are no particles, then the system should be 0 K (like you pointed out). What I'd like to know is if you have a true vacuum (i.e. there are no particles in the container whatsoever) then the temperature of the system should remain at 0 K even if it were placed in someplace very hot, like the center of the sun.

-- Anonymous, February 18, 2000

That is an interesting discussion. I beleive most of what you said is correct. Since, I assume you began this discussion in reference to the exam questions, all I can say is if you perform something in the vacuum, that only the materials involved in the process are what is present. Although this does negate the option of having a "true" vacuum, I think that you are supposed to assume that there is "no" pressure. As to dealing with the temperature issue, I am not sure I can help you. Maybe somebody else can...

-- Anonymous, February 18, 2000