Phase Rule and Phase Equilibria

1
Phase Rule and Phase Equilibria
2
Two-component Systems Containing Solid and Liquid
Phases

• Solid- liquid mixtures in which 2 components are
  completely miscible in the liquid state and
  completely immiscible as solid.
• Examples of such systems are
• Salol thymol.
• Salol camphor.

3
100 thymol
100 salol
Increasing the of thymol in the mixture
till reaching 100 .
4
The phase diagram for the salol thymol system

• Single liquid phase,
• (ii) Region containing solid salol and a
  conjugate
• liquid phase,
• (iii) Region in which solid thymol is in
  equilibrium with
• a conjugate liquid phase.
• Region in which both components are present as
• pure solid phases.
• Those regions containing two phases (ii, iii,
  and iv) are comparable to the two-phase region of
  the phenol-water system.

5
F2-211
6

• System is represented by point X (60 by weight
  of thymol in salol) temperature
  (50 o C)
• On cooling the system, the following sequence of
  the phase occurs
• The system remains as a single liquid until
  29oC.
• At 29oC a minute amount of solid
  thymol
• At 25oC, (system X1) a liquid phase,
  a1 (53 thymol in salol) and b1 (pure solid
  thymol).
• At 20oC, (system X2) the liquid phase
  is a2 (45. by weight of thymol in salol), b2
  (pure solid thymol).
• At 15oC, (system X3) the liquid
  phase a3 is 37 thymol in salol and b1 (pure
  solid thymol).

7

• Below 13 o C the liquid phase disappears
  altogether and the system contains two solid
  phases of pure salol and pure thymol.
• At 10oC (point X4), the system contains an
  equilibrium of a4 b4 (pure solid thymol pure
  solid salol).
• The lowest temperature at which liquid phase
  coexists is known as eutectic point.
• In case of thymol / salol system the eutectic
  point is 13 o C ( 3 phases liquid, solid
  salol solid thymol)

8

• The eutectic point therefore denotes an invariant
  system for, in a condensed system
• F 2 - 3 1 0.
• Substances forming eutectic mixtures (e.g.,
  camphor, chloral hydrate, menthol, and
  betanaphthol).
• If such combinations is dispensed as dry
  powder, drying may be achieved by the addition
  of an absorbent powder such as kaolin or light
  magnesium oxide.

9
Phase Equilibria in Three-Component System

• In systems containing three components but only
  one phase,
• F 3 - 1 2 4
• For non-condensed system. The four degrees of
  freedom are temperature, pressure the
  concentration of 2 of the 3 components.
• For condensed the temperature is kept
• constant, then F 2 .

T
constant
4
P
condensed
C2
C 1
10
Ternary System with One Pair of Partially
Miscible Liquids

• Water and benzene are partially miscible system
• two-phase system.

benzene saturated with water
2 phase system
water saturated with benzene
Addition of alcohol (solvent effect)
1- phase system
11
Mixture 60 B, 20 A, 20 C.
12
Alcohol
water
benzene
A, B C represent water, alcohol benzene,
respectively. AC binary mixture of
A and C. a c are the limits of solubility of
C in A and A in C.
13

• System (g) after reaching equilibrium, will
  separate into two
• phases, (f ) and ( i).
• weight of phase f /weight of phase I gi /
  fg.
• Mixture h, mid point of the tie line, will
  contain equal weights of
• the two phases at equilibrium.

14

• The curve a f d e i c, a binodal
  curve (the extent
• of the two-phase region).
• The remainder of the triangle contains one
  liquid
• phase.
• The directions of the tie lines are related to
  the shape
• of binodal, (depends on the relative
  solubility of 3rd
• component (alcohol) in the other 2
  components).
• when the added component acts equally on the
  other
• two components to bring them into solution
• binodal be symmetric the tie
  lines are parallel
• to the base line.

15
Effect of Temperature

• Changes in temperature will cause the area of
  immiscibility, (the
• binodal curve) to change.
• Area of the binodal as the temperature is
  miscibility is
• A point is reached at which complete miscibility
  is obtained and the
• binodal vanishes.

16
Ternary Systems with Two or Three Pairs of
Partially Miscible Liquids
A C , B C show partial miscibility. A and B
are completely miscible at the temperature used.
Temperature gradually leads to a
reduction in the areas of the two binodal curves
their eventual disappearance. (c)
Temperature expands the binodal curves. At a
sufficiently low temperature, they meet and fuse
to form a single band of immiscibility as shown
in (a).
17
Systems containing three pairs of partially
miscible liquids

• 3 binodal curves meet, a central region
  appears in which 3
• conjugate liquid phases exist in equilibrium.
  
• In this region, D, which is triangular, F 0
  ( condensed system
• under isothermal conditions).
• All systems lying within this region consist of
  3 phases whose
• composition are always given by the points x,
  y z.
• The only quantity that varies is the relative
  amounts of these 3
• conjugate phases.

18
One phase
2 phases
3 phases
X
A, B, C
Y
Z
19
Arrangement of three phases It depends on the
composition of the phases

• At point D , F 0 ??????