What will happen if you put some 20 ∘c water in a vacuum chamber and reduce the pressure to less than 18 mmhg?
The answer is the water will boil. The water boils because of a reduction in the air pressure due to the reduced weight of air column above. This also reduces the collision of water molecules with air molecules at the surface hence allowing the water molecules to easily escape into the atmosphere. This means that the boiling point of the water is easily reached under low air pressure.