Answer to Question #173426 in Molecular Physics | Thermodynamics for Fabio Corrieri

Question

when water solidifies it increases its size....... does it behaves like this in vacuum as well???

Answer 1

If you brought liquid water into outer space, would it freeze or would it boil? The vacuum of space is awfully different from what we’re used to here on Earth. Where you stand now, surrounded by our atmosphere and relatively close to the Sun, the conditions are just right for liquid water to stably exist almost everywhere on our planet’s surface, whether it’s day or night.

But space is different in two extremely important ways: it’s cold (especially if you’re not in direct sunlight, or farther away from our star), and it’s the best pressureless vacuum we know of.

So, if you take water into space, it should freeze, right? Not so fast! Because if you take liquid water and you drop the pressure in the environment around it, it boils. You might be familiar with the fact that water boils at a lower temperature at high altitudes; this is because there’s less atmosphere above you, and hence the pressure is lower. We can find an even more severe example of this effect, however, if we put liquid water in a vacuum chamber, and then rapidly evacuate the air. What happens to the water?

It boils, and it boils quite violently at that! The reason for this is that water, in its liquid phase, requires both a certain range of pressure and a certain range of temperatures. If you start with liquid water at a given fixed temperature, a low enough pressure will cause the water to immediately boil.