When heating a liquid

Liquid

Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...

 consisting of two or more components, the bubble point is the point where first bubble of vapor

Vapor

A vapor or vapour is a substance in the gas phase at a temperature lower than its critical point....

 is formed. Given that vapor will probably have a different composition than the liquid, the bubble point (along with the dew point

Dew point

The dew point is the temperature to which a given parcel of humid air must be cooled, at constant barometric pressure, for water vapor to condense into liquid water. The condensed water is called dew when it forms on a solid surface. The dew point is a saturation temperature.The dew point is...

) at different compositions are useful data when designing distillation systems.

For single component mixtures the bubble point and the dew point are the same and are referred to as the boiling point

Boiling point

The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

.

Calculating the bubble point

At the bubble point, the following relationship holds:



where
.
K is the distribution coefficient or K factor, defined as the ratio of mole fraction in the vapor phase to the mole fraction in the liquid phase at equilibrium.


When Raoult's law and Dalton's law

Dalton's law

In chemistry and physics, Dalton's law states that the total pressure exerted by a gaseous mixture is equal to the sum of the partial pressures of each individual component in a gas mixture...

hold for the mixture, the K factor is defined as the ratio of the vapor pressure to the total pressure of the system: