When heating a liquid
consisting of two or more components, the bubble point
is the point where first bubble of vapor
is formed. Given that vapor will probably have a different composition to the liquid, the bubble point (along with the dew point
) 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.
Calculating the bubble point
At the bubble point, the following relationship holds:
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
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: