CHAPTER 13 THE PHASE RULE AND PHASE DIAGRAMS
13.2 PHASEDIAGRAMS: BINARYSYSTEMS 437
xATgl(^0) zA 1
(a)
xA
T
g
l
(^0) zA 1
(b)
xA
T
g
l
(^0) zA 1
(c)
Figure 13.10 Temperature–composition phase diagrams of binary systems exhibit-
ing (a) no azeotropy, (b) a minimum-boiling azeotrope, and (c) a maximum-boiling
azeotrope. Only the one-phase areas are labeled; two-phase areas are hatched in the
direction of the tie lines.
xA
T
g
l
l
β
α
(^0) zA 1
(a)
xA
T
g
l
l
β
α
(^0) zA 1
(b)
xA
T
g
lβ lα
(^0) zA 1
(c)
Figure 13.11 Temperature–composition phase diagrams of binary systems with
partially-miscible liquids exhibiting (a) the ability to be separated into pure compo-
nents by fractional distillation, (b) a minimum-boiling azeotrope, and (c) boiling at a
lower temperature than the boiling point of either pure component. Only the one-phase
areas are labeled; two-phase areas are hatched in the direction of the tie lines.
abbreviated A, AB, AB 3 , and AB 5. The following dissociation equilibria (dehydration
equilibria) are possible:
CuSO 4 H 2 O.s/ïCuSO 4 .s/CH 2 O.g/
1
2 CuSO^4 3H^2 O.s/ï
1
2 CuSO^4 H^2 O.s/CH^2 O.g/
1
2 CuSO^4 5H^2 O.s/ï
1
2 CuSO^4 3H^2 O.s/CH^2 O.g/
The equilibria are written above with coefficients that make the coefficient of H 2 O(g) unity.
When one of these equilibria is established in the system, there are two components and
three phases; the phase rule then tells us the system is univariant and the pressure has only
one possible value at a given temperature. This pressure is called thedissociation pressure
of the higher hydrate.