freeze or boil

[claymore]

Saw this question in a science mag but never got the next edition to find the answer........If they emptied a bucket of water outside the space station would it boil because of the low pressure or freeze because of the low temperature?

[Clanad]

Boiling of water is somewhat a misnomer because most of us equate the roiling action with high temperatures... 212 degrees Fharenheit at sea level... But, here in the inter-mountain area of the western U.S. where I live, water will "boil" at much lower temperatures simply because of the altitude. It takes along time to hard-boil an egg, for example. The altitude, as you've already surmised, equates with lower air pressure, which is what caused the air in the water to remain in suspension in the first place. Therefore, liquid water suddenly exposed to zero air pressure will "boil" immediately before it has the chance to freeze. In fact, if one had the ability to throw a handfull of ice cubes into the same "space", they would evaporate in the same way, which is called sublimation... (Think nearly empty ice cube tray you placed in the freezer a month ago)...

[Teddio]

This is not an easy question to answer. Is the water at room temperature and impure? If so it would boil and its temperature would fall rapidly to zero Celsius. To change phase from liquid to gas, the water would need to extract 2.2 Megajoules of heat energy per kilogram from itself.
Ambient temperature has no meaning in the vacuum of space. For the water to freeze it must lose 0.33 Megajoules of heat energy per kilogram. The only mechanism for this is infrared radiation loss. However the Sun and Earth are emitters of IR radiation so the ice would reach an equilibrium temperature. Ice at zero Celsius has a vapour pressure greater than zero and so would sublime. Very cold ice has a lower vapour pressure. Icy bodies such as comets sublime when they come near to the Sun. Very cold icy bodies such as the Kuiper Belt objects show negligible rates of sublimation since their very thin atmospheres have a pressure greater than the vapour pressure of the icy surface.