Boiling water at reduced pressure – Water boils at 75 oC

At sea level (where most of us are), the standard atmospheric pressure is about 101325 Pa. The boiling point of water is at 100 oC which we are familiar with.

But as you climbed up e.g. Mount Everest at 8,848 m, the pressure is low and the boiling point of the water is about 71oC. So that’s the hottest cofe you can have on top of the cold mountain!

Hence as the pressure decreases, the boiling point of the water decreases. As with lower pressure, the water molecules requires lesser energy to break the intermolecular forces to escape into the atmosphere, hence boiling point is lower.

This video shows the same effect. Using the syringe, the air is pumped out of the container to reduce the pressure. The water at 75 oC , (below the usual boiling point of 100 oC) will start to boil and you can observe the bubbles forming!