Chemistry 232

1
Chemistry 232

• Multicomponent Phase Equilibria

2
Raoults Law

• Variation in the total vapour pressure of a two
  component liquid mixture according to Raoults
  Law

PB
XA
3
The Variation in Terms of Gas Phase Mole
Fractions

• yA the vapour phase mole fraction of A.

PA
liquid
vapour
PB
yA
4
A Liquid-vapour Phase Diagram

• composition axis

liquid
PA
vapour
PB
ZA
5
A Blow-up of the Two-phase Region
6
Moving Down an Isopleth

• isopleth - constant total composition
• lever rule nl ln

450
liquid
a
350
P (torr)
b
c
l
n
300
n
l
d
250
vapour
e
200
0.25
1.00
0.75
0.50
0.0
ZA
7
Temperature-composition Phase Diagrams
TB
T / K

• TA

xA
yA
ZA
8
Simple Distillation of Liquid Mixtures

• Vapour at composition a2 is condensed, it
  becomes richer in the more volatile component.

TB
a2
T / K
a2
boil
condense
a1
TA
a3
ZA
9
Fractional Distillations

• Repeat the evaporation and condensation cycle!

10
Azeotropes

• A low boiling azeotrope.

11
Azeotropes

• A High Boiling Azeotrope

12
Liquid-Liquid Phase Diagrams

• TUC - the upper critical temperature.

Tuc
T / K
13
Liquid-Liquid Phase Diagrams

• TLC - the lower critical temperature.

T / K
F2
14
Liquid-Liquid Phase Diagrams

• A system exhibiting and upper and a lower
  critical solution temperature!

TUC
T / K
TLC
XA
15
The distillation of partially miscible liquids

• Complete miscibility occurs before boiling
  commences.

T / K
16
The distillation of partially miscible liquids

• Liquids remain immiscible even up to the boiling
  temperature.

T / K
ZA
17
Liquid-Solid Phase Diagrams

• Freezing points of solutions are dependent on the
  compositions of the solutions!
• We have already examined briefly the freezing
  point depression of dilute soutions.
• where ?fus,AH enthalpy of fusion of A
• TA and TA are the freezing points of the
  solution and pure A, respectively.

18
The Liquidus Curve for B in A

• For a solution of B in liquid A.

TA
T/K
liquid
solid
liquidus curve
XA
19
The Liquidus Curve for A in B

• For a solution of A in liquid B.

TB
liquidus curve
T/K
liquid
solid
XA
20
The S-L Phase Diagram

• Overlapping the curves leads to the liquid-solid
  phase diagram for A and B.

liquid
TA
eutectic
TB
solid A solution
solid B solution
solid A solid B
21
A Blow-up of the Two-phase Region

• Tie lines connect the liquid phase of specified
  composition in equilibrium with either solid A or
  B.

TA
liquid
TB
tie line
eutectic
solid A solution
solid B solution
solid A solid B