PHYSICAL CHEMISTRY IN BRIEF

CHAP. 7: PHASE EQUILIBRIA [CONTENTS] 197

p

p 1

p 2

ps 1

ps 2

p

0 x 1 1

Obr.7.5:Dependence of the total pressurepand partial pressuresp 1 andp 2 on the composition of
the liquid phase in a two-component system. The line segments represent the relations for an ideal
mixture.ps 1 andps 2 are the saturated vapour pressures of the individual components.

whereγi is the activity coefficient of componentiin a liquid mixture, which is defined by
relation (6.99).

Note:Equation (7.24) is a very good approximation for equilibria at not very high pres-

sures.

Example

Calculate the activity coefficients of water and ethanol in the system ethanol (1)—water (2) at

70 ◦C using the following data: x 1 = 0.252; y 1 = 0.552; p= 62. 39 kPa; ps 1 = 72. 3 kPa; ps 2 =

31. 09 kPa.