1. PC-1(B): PHASE EQUILIBRIA
LECTURE NOTES & Synopsis

2. TERMS & Examples Solid Liquid (Melting)
Homogenous Chemical Equilibrium
N2(g) + 3H2(g) NH3(g)
Heterogonous Chemical Equilibrium
CaCO3(s) CaO(s) + CO2(g)
Heterogonous Physical Equilibrium
Solid Liquid (Melting)
Liquid Vapour (Vaporisation)
Solid Vapour (Sublimation)

3. TERMS & Examples (Contd….)
PHASE , P : Physically distinct & mechanically separable
COMPONENTS , C : Minimum number of chemical species by means of which the composition each phase can be described
C = Number of chemical compounds – No of chemical and or physical
( material or charge balance ) relations existing with them
(i) WATER SYTEM: ice water vapor
P = 1, 2 or 3 ; C = 1 ; F = ?
(ii) SYSTEM OF (PCl5 + PCl3 + Cl2 )
PCl PCl3 + Cl2 ; P= ; C = 3 – 1 = 2 ; F = ?

4. TERMS & Examples (Contd…..)
(iii) Pb & Ag System
C= 2 ; P = 1, 2 or 3 ; F = 2 , 1 , 0
NB : There are no (chem or phys) relation between
Pb & Ag
% Pb = % Ag is only a mathematical
relation
DEGREES OF FREEDOM , F (Variables) : Minimum
number of independent variables that must be fixed in order to understand the system fully.
The values of P & F depend on the condition

5. PHASE RULE - Derivation
F = C-P+2 (Gibbs Phase Rule)
Degrees of freedom (F)
= Total No of variables – Total No of
equations connecting them.
Total No of variables:
Conc.variables
C-1 for each phase
P(C-1) for all P phases + 2 ( For P & T)

6. PHASE RULE – Derivation (Contd…)
Total No of equations
P-1 (For each component) ;
C( P-1) For all the ‘ C ’ components
Hence , F = {P(C-1)+2} – C( P-1)
= C-P + 2

7. PHASE CHANGES Clapeyron equation dp/dT = ∆H/(T∆V)
dG=VdP-SdT = 0 (For equilibrium)
Clapeyron equation
dp/dT = ∆H/(T∆V)
Solid Liquid (Fusion or Melting)
Clausius-Clapeyron equations (Vapors)
d(lnp)/dT = ∆H/(RT 2)
Liquid Vapour (Vaporisation)
Solid Vapour (Sublimation)

8. SYSTEMS TO BE STUDIED PHASE DIAGRAM OF One Component Systems
Water system
Sulphur system
Two Component System
Simple eutectic system - Lead-Silver system
Compounds with congruent melting point.
Ferric chloride-water system
Compounds with incongruent melting point(SS).
Sodium sulphate-water system
Three component system.

9. Water system

10. Water System-Discussion
Curves-Sublimation, Vaporization, Fusion
Meta stable equilibrium curve
Ice Water curve has –ve slope
M.P of ice decreases with increase in p
Areas :F= 2 ; Lines :F= 1
Triple point:F = 0,0.0075ºC,4.58 mm Hg
Critical state 374ºC , 218 atm

11. SULPHUR SYSTEM

12. Simple eutectic system-General

13. Simple Eutectic(Lead-Silver System)

14. Compounds formation with congruent melting point.

15. Ferric chloride-Water system

16. Fe2Cl6 –Water System : Details
POSITIONS
PHASE (S) at Equilibrium C P
Temp F A
Ice(s) 1 2
0°C
Curve-AB
Ice(s)+ Solution of Fe2Cl6 B
Ice(s) + Solution of Fe2Cl6 + Fe2Cl6.12H2O(s) 3
-55°C
Curve-BC
Solution of Fe2Cl6 + Fe2Cl6.12H2O(s)
Fe2Cl6.12H2O(s) + Solution of Fe2Cl6
37°C
Curve-CD D
Fe2Cl6.12H2O(s) + Solution of Fe2Cl6 + Fe2Cl6.7H2O(s)
26°C
Curve-DE
Solution of Fe2Cl6 + Fe2Cl6.7H2O(s) E
Fe2Cl6.7H2O(s) + Solution of Fe2Cl6
32.5°C
Curve-EF

17. Fe2Cl6 –Water System : Details (Contd…..)
POSITIONS
PHASE (S) at Equilibrium C P
Temp F
Fe2Cl6.7H2O(s) + Solution of Fe2Cl6 + Fe2Cl6.5H2O(s) 2 3
30°C
Curve-FG
Solution of Fe2Cl6 + Fe2Cl6.5H2O(s) 1 G
Fe2Cl6.5H2O(s) + Solution of Fe2Cl6
56°C
Curve- GH H
Fe2Cl6.5H2O(s) + Solution of Fe2Cl6 + Fe2Cl6.4H2O(s)
55°C
Curve-HJ
Solution of Fe2Cl6 + Fe2Cl6.4H2O(s) J
Fe2Cl6.4H2O(s) + Solution of Fe2Cl6
73.5°C
Curve-JK K
Fe2Cl6.4H2O(s) + Solution of Fe2Cl6 + Fe2Cl6(s)
66°C
Curve- KL
Solution of Fe2Cl6 + Fe2Cl6(s)

18. Compound with incongruent melting point
Compound with incongruent melting point. Peritectic Reaction(Change)-General

19. Compound formation with incongruentmelting point-Examples
NaCl-Water (NaCl.2H2O)
CaCl2-Water (CaCl2.6H2O)
Na2SO4-Water
(Na2SO4.10H2O, Na2SO4.7H2O & Na2SO4.4H2O)

20. Sodium sulphate-Water Perttectic Change

21. Uses of Eutectic Systems (Freezing mixtures)
% Salt in the Eutectic
Eutectic Temperature ºC
NaCl.2H2O-Ice 23
-22
KI-Ice 52
-23
CaCl2.6H2O-Ice
15.2
-55.9
NaNO3-Ice
33.3
-18.1
NH4Cl-Ice
20.1
-16

22. Uses of Eutectic Systems (Low melting alloys)
Wood metal:50% Bi ; 25%Pb; 12.5%Sn & 12.5%Cd-mp=65ºC
Safety devices: Fuse wires ; Plugs

23. TRI ANGULAR COORDINATE SYSTEM (Three component system)

24. Examples of Three component Systems
One pair of partially miscible liquid pair
CH3COOH,CHCl3 & H2O
Two pairs of partially miscible liquid pair
Three pairs of partially miscible liquid pair

25. Three component system (Acetic acid, Choloroform &Water)
CHCl3-H2O-partially miscible pair

26. THREE COMPONENT SYSTEM Two simple salts & water