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% salol
100% thymol
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. F=2-2+1=1

6. On cooling the system, the following sequence of the phase occurs:
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). z

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
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 = = 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
C 1 C2

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. 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 ??????