Not many of us have had the opportunity to put water in a vacuum chamber and observe what happens to it. So we are going to take you along with our exploration and show you what happens to the water, as you expose it to the vacuum, or more generally, the outer space. (Which is not a perfect vacuum anyway!)
Water at sea level
When the water is at sea level, it is exposed to the standard atmospheric pressure and temperature (1 atm and 0 °C), where it vaporizes gradually (evaporates), just like the rest of the water in the world. But when you start adding heat to boil it, the water vaporizes faster (boils) as soon as it reaches the boiling point, and continues to vaporize at that rate until the temperature drops below the boiling point, i.e. you remove the heat source.
The water boils the moment when the vapor pressure that builds up above the water surface, becomes equal to the atmospheric pressure. The temperature at which this happens is the boiling point of the water, and at sea level, it is 100 °C. This boiling point can be decreased for any liquids by boiling them at lower atmospheric pressures. Now with this knowledge, we can explain what happens if we increase the altitude.
Water at the Everest
Before we launch ourselves straight into space, let’s try putting our water beaker on the Everest and explore the changes in it. The top point of the Everest is 8848 meters above the sea level, and at this height, the atmospheric pressure is 0.34 atm, which is lower than that of the sea level, which is 1 atm.
When you boil any liquid in such lower pressure, the temperature required to attain the equilibrium vapor pressure is much lower. This reduces the boiling point of the liquid.
In the case of water here, the boiling point would be lower too. As the atmospheric pressure is less at the Everest, the pressure exerted on the surface of the water would be less and the vapor pressure required for the equilibrium condition would be less too. The equilibrium vapor pressure is attained at 71 °C and the water starts boiling, as you heat it to the same temperature.
Water in vacuum or space
So now, we are in a spaceship with your beaker of water, waiting to be released into the dark and cold vacuum. The minimum temperature of the space is about 2.7 K or -270.45 °C (energy radiated by cosmic background radiation), which is a little above the absolute zero (0 K or -273.15 °C). The pressure will be negligible.
Now, we eject the beaker into the void. As it floats, the water inside the beaker boils instantly. The instantaneous boiling occurs, as the boiling point of the water is too low due to the negligible pressure in space. As the water vaporizes using the heat energy from the rest of the liquid water, the temperature of the water also reduces to the point where the rest of the water freezes. Besides this, the lower temperature of the vacuum also freezes (deposition) the water vapor, turning them into solid crystals. What left in the beaker will be solid ice. So when you expose water into space or vacuum, both boiling and freezing occurs.
Thought the space ride wasn’t that dramatic, I hope you learned something today. Send all your follow-up questions and discussion points to us either via the discussion box below or via our contact form. We would be happy to answer your questions and further explore with you.