PHYSICAL CHEMISTRY IN BRIEF

CHAP. 7: PHASE EQUILIBRIA [CONTENTS] 200

T

Tb, 2

Tb, 1

s

A

(g)

i



(g)+(l)

(l)

0 y 1 x 1 x′ 1 y 1 ′ 1

Obr.7.7:Isobaric diagram of a two-component system with an azeotropic point. The upper curve
shows the dependence of dew temperatures on the molar fraction of component 1 while the lower curve
represents the dependence of boiling temperatures.Tb, 1 andTb, 2 are the boiling temperatures of the
pure components.

Note:An azeotrope cannot occur in ideal solutions.

Example

In the binary system tetrachlormethane(1)—ethanol(2), an azeotropic point was measured at

65.08◦C and a total pressure of 101 kPa. Under these conditions the vapour phase behaves

as an ideal gas. What are the values of the activity coefficients at this point if at the given

temperature the saturated vapour pressures of the individual components areps 1 = 70. 78 kPa and

ps 2 = 59. 84 kPa?