The boiling point of a liquid is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. At this point, bubbles of vapor form inside the liquid, and then break out from the surface.

The boiling point depends on several factors:

The type of material from which the substance is made. The more tightly packed together molecules are, the harder it is for them to escape as gaseous molecules. This means that heavier elements like gold or lead have higher boiling points than lighter elements like helium or hydrogen.

The size of particles in a compound. Large particles have more surface area from which molecules can escape as gas than small ones do.

The pressure at which you heat it. The higher the pressure, the harder it is for molecules to escape as gas — so when cooking at high altitudes, water boils at lower temperatures than it does at sea level because there’s less atmospheric pressure above us than down here on Earth’s surface.

Last modified: October 9, 2022