View Full Version : Why does everything freeze in space without pressure?
Speaker for the Dead
03-11-2001, 10:55 AM
From what I remember, the lower the pressure, the lower the boiling point. However, I also remember that the lower the temp, the higher chance that it's frozen (our imaginary substance). So why are a lot of things frozen in space instead of gas. I realize that things like hydrogen and helium are still gasses because of their incredibly low freezing point, but why not anything else?
03-11-2001, 11:09 AM
The relationships between state, pressure and temperature are more complicated than you suppose. To tell what state a substance will be in space, you really have to look at the phase diagram.
For instance, here's the one for water: http://www.sbu.ac.uk/water/phase.html
At a pressure of 0 Pa (a vacuum), the temperature still has to be above 200 K for water to be a gas. Below 200 K it will be ice. So in space it will be ice.
03-11-2001, 11:09 AM
When you lower atmospheric pressure, not only do you lower the boiling point, but you raise the freezing point.
In space water boils and freeze at the same time; there is no liquid phase to water in space and therefore goes directly from ice to vapor (Sublimation)
Dry ice (frozen carbon dioxide) does the same thing here on earth
03-11-2001, 11:10 AM
I am not a physics maven but as a WAG I think you may be apple and oranging by comparing outer space to general rules for freezing/boiling with terresterial atmospheric pressure involved. Outer space is very low pressure and extremely cold. I would imagine it is cold enough so that the relative lack of pressure is inconsequential with respect to freezing.
Forewarning to the physics mavens if I'm wrong I *said* it was a WAG.
03-11-2001, 12:43 PM
SmackFu has the correct answer.
03-11-2001, 04:11 PM
Anyone notice that that water site (a great site, by the way) has an explanation (http://www.sbu.ac.uk/water/explan.html#mpemba) of why hot water may freeze faster than cold water? It's the Mpemba Effect... :)
Ref: Cecil's wisdom (http://www.straightdope.com/classics/a2_098b) and The "Comments on Cecil's Column's" discussion (http://boards.straightdope.com/sdmb/showthread.php?threadid=49867)
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