Boiling Point

When a liquid is heated in an open container, the vapor pressure increases until it becomes equal to the pressure above the liquid. At this point the average kinetic energy of the molecules is such that they are rapidly converted from the liquid to the vapor phase within the liquid as well as at the surface. The temperature at which this occurs is known as the boiling point. So boiling point is defined as the temperature at which the vapor pressure of a liquid equals the atmospheric pressure.