PHYSICAL CHEMISTRY IN BRIEF

CHAP. 7: PHASE EQUILIBRIA [CONTENTS] 201

0 x^11

0

1

y 1

6

x 1 =y 1

Obr.7.8:y−xdiagrams of two two-component systems. The bold line shows the dependence of the
vapour phase composition on the liquid phase composition for a system with a positive azeotrope; the
azeotropic point is indicated by the arrow. The thinner line shows the same dependence for a system
without an azeotropic point.

Solution

From relations (7.24) and (7.26) it follows that at the azeotropic point

γi=p/psi

and thusγ 1 = 1. 43 andγ 2 = 1. 69.

Note: In order to compare mutual volatility of two components in a mixture,relative

volatilityis defined as

αij=

yixj

xiyj

. (7.30)

From (7.26) we can see that at the azeotropic point, relative volatilities equal 1.

Azeotropic point in a two-component system