thermodynamics Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of the ...

, the bubble point is the

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

(at a given

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

) where the first bubble of

vapor In physics, a vapor (American English) or vapour (British English and Canadian English; American and British English spelling differences#-our, -or, see spelling differences) is a substance in the gas phase at a temperature lower than its critic ...

is formed when heating a

liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, a ...

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 The dew point is the temperature to which air must be cooled to become saturated with water vapor, assuming constant air pressure and water content. When cooled below the dew point, moisture capacity is reduced and airborne water vapor will cond ...

) 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 The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding envir ...

Calculating the bubble point

At the bubble point, the following relationship holds:
:

\sum_^ y_i = \sum_^ K_i x_i = 1

where
:

K_i \equiv \frac

. K is the ''distribution coefficient'' or ''K factor'', defined as the ratio of mole fraction in the vapor phase

\big(y_\big)

to the mole fraction in the liquid phase

\big(x_\big)

at equilibrium.
When Raoult's law and

Dalton's law Dalton's law (also called Dalton's law of partial pressures) states that in a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases. This empirical law was observed by Jo ...

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

K_i = \frac

Given either of

x_i

y_i

and either the temperature or pressure of a two-component system, calculations can be performed to determine the unknown information. {{Citation , last1 = Smith, first1 = J. M. , last2 = Van Ness, first2 = H. C. , last3 = Abbott, first3 = M. M. , title = Introduction to Chemical Engineering Thermodynamics , place = New York , publisher = McGraw-Hill , year = 2005 , location = , pages = 351 , volume = , edition = seventh , url = , doi = , id = , isbn = 0-07-310445-0

Calculating the bubble point

References

See also