PHYSICAL CHEMISTRY IN BRIEF

CHAP. 7: PHASE EQUILIBRIA [CONTENTS] 224

a) b)

(g)

(s 2 ) + (g) (g) + (s^1 )

E

E

(s 2 ) + (s 1 )

(g)

(s 2 ) + (s 1 )

(s 2 ) + (g)

(g) + (s 1 )

0 x 1 1 0 x 1 1

Ts 2

T

Ts 1

p

pss 2

pss 1

Obr.7.16:Solid-gas phase equilibrium in two-component systems whose components are immiscible
in the solid phase: a) Dependence of the temperature of sublimation on composition (isobaric diagram);
b) dependence of the pressure of sublimation on composition (isothermal diagram).

of the gaseous phase, we may replace the sublimation volume with the volume of an ideal gas
∆subVi=. RT /p. Then for the molar fractions of the components in the gaseous phase it applies
that

yi(g)=

psi

p

. (7.71)

The pressure dependence of the vapour phase composition is shown in Figure7.16b.