In thermodynamics, the bubble point is the temperature (at a given pressure) where the first bubble of vapor is formed when heating a liquid consisting of two or more components. Given that vapor will probably have a different composition than the liquid, the bubble point (along with the dew point) at different compositions are useful data when designing distillation systems.
For a single component the bubble point and the dew point are the same and are referred to as the boiling point.
At the bubble point, the following relationship holds:<br>
<br> where<br>
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. <br> When Raoult's law and Dalton's law hold for the mixture, the K factor is defined as the ratio of the vapor pressure to the total pressure of the system:<br>
Given either of or and either the temperature or pressure of a two-component system, calculations can be performed to determine the unknown information.