Atmospheric Pressure and Boiling

The boiling point of a liquid is directly affected by atmospheric pressure. This is the pressure exerted by the weight of the air molecules above the liquid.

Video: Boiling & Atmospheric Pressure

In an open system this is called atmospheric pressure. The greater the pressure, the more energy required for liquids to boil, and the higher the boiling point. In an open system this can be visualized as air molecules colliding with the surface of the liquid and creating pressure. This pressure is transmitted throughout the liquid and makes it more difficult for bubbles to form and for boiling to take place. When the pressure is reduced, the liquid requires less energy to change to a gaseous phase and boiling occurs at a lower temperature.

Atmospheric pressure is sometimes called barometric pressure. On Earth the atmospheric pressure (at sea level) is defined as 1 atmosphere (atm). Pure water boils at 100 degrees Celsius at Standard Pressure (1 atm).