Here's why:
* Vapor Pressure: The pressure exerted by the vapor of a liquid when it's in equilibrium with its liquid phase.
* External Pressure: The pressure of the surrounding environment.
When the vapor pressure of a liquid equals the external pressure, the liquid has enough energy to overcome the external pressure and escape into the gas phase. This is what we observe as boiling.
Important Note: The boiling point is dependent on the external pressure. At higher altitudes, where the atmospheric pressure is lower, water boils at a lower temperature.
