1. OUTLINE
PHASE RULE
WHAT IS MEANT BY PHASE
WHAT IS MEANT BY COMPONENTS
DEGREES OF FREEDOM
DERIVATION
ONE COMPONENT SYSTEM
PHASE DIAGRAM
2. PHASE RULE
THE PHASE RULE IS AN IMPORTANT
GENERALIZATION DEALING WITH THE
BEHAVIOR OF HETEROGENEOUS SYSTEM.
IN GENERAL IT MAY BE SAID THAT WITH THE
APPLICATION OF PHASE RULE IT IS POSSIBLE
TO PREDICT QUALITATIVELY BY MEANS OF
DIAGRAM. THE EFFECT OF CHANGING
PRESSURE , TEMPERATURE AND
CONCENTRATION ON A HETEROGENEOUS
SYSTEM IN EQUILIBRIUM.
3. HETEROGENEOUS EQUILIBRIUM IS
FIRST DISCOVERED BY AMERICAN
PHYSICIST “WILLARD GIBBS” IN 1874.
IT MAY BE MATHEMATICALLY STATED
AS:
F=C – P+2
F= DEGREE OF FREEDOM
C=COMPONENTS
P=NUMBER OF PHASES OF THE
SYSTEM
4. PHASE
IT MAY BE DEFINED AS:
“ANY HOMOGENOUS PART OF A SYSTEM HAVING
ALL PHYSICAL AND CHEMICAL PROPERTIES THE
SAME THROUGHOUT”.
A PHASE MAY BE OF THREE TYPES:
1. ONE PHASE SYSTEM
2. TWO PHASE SYSTEM
3.THREE PHASE SYSTEM
5. A SYSTEM CONSISTING OF ONE PHASE IS
CALLED HOMOGENOUS SYSTEM.
A SYSTEM CONSIST OF TWO OR MORE
SYSTEM IS CALLED HETEROGENOUS
SYSTEM.
GENERALY,LIQUID SLOID GASES ARE
THREE PHASES BUT IIN PHASE RULE “A
UNIFORM PART OF A SYSTEM IN
EQUILIBRIUM IS TERMED AS A PHASE.
6. EXAMPLES:
1.PURE SUBSTANCES, MAY BE LIQUID, SOLIS OR GAS
FORM 1 PHASE.
E.G, OXYGEN,BENZEN AND ICE ARE 1- PHASE.
2.MIXTURE OF GASES, IS ONE PHASE SYSTEM.E.G, ANY
MIXTURE OF GASES LIKE OXYGEN AND NITROGEN FORN
1-PHASE.
3.MISCIBLE LIQUIDS, TWO MISCIBLE LIQUIDS FORM ONE
PHASE.E.G, SOLUTION OF WATER AND ETHANOL IS ONE
PHASE SYSTEM.
4.NON-MISCIBLE LIQUIDS,SOLUTION OF TWO NON
MICIBLE LIQUIDS FORM TWO SEPRATE LAYER N IT WILL
2 PHASE SYSTEM.E.G, MIXTURE OF CHLOROFORM AND
WATER CONSTITUTE 2-PHASE SYSTEM.
7. 5.AQUEOUS SOLUTION,AN AQOUES SOLUTION
LIKE WATER+ SUGER FORM AQUEOUS SOLUTION
AND IT WILL ONE PHASE SYSTEM.
BUT SATURATED SYSTEM OF THAT SOLUTION
WILL FORM 2 PHASE SYSTEM.
AQOUES SOLUTION OF SODIUM CHLORIDE IS 1-
PHASE SYSTEM WHILE ITS SATURATED SYSTEM
FORM 2-PHASE SYSTEM
6.MIXTURE OF SOLIDS:
A. A PHASE HAVE SAME PHYSICAL AND CHEMICAL
PROPERTIES.
A MONOCLINIC AND RHOMBIC SULPHUR ARE TWO
ALLOTROPIC FORMS WHICH ARE CHEMICALLY
SAME BUT PHYSICALLY DIFFERENT AND FORMS 2-
PHASE SYSTEM.
8. B. A MIXTURE OF TWO OR MORE CHEMICAL
SUBSTANCES CONTAINS AS MANY PHASES.EACH
OF THEM HAVE DIFFERENT CHEMICAL AND
PHYSICALL PROPERTIES.
A MIXTURE OF CALCIUM CARBONATE AND
CALCIUM OXIDE FORM TWO PHASES.WHILE THE
DECOMPOSITION OF CALCIUM CARBONATE
FORMS 3 PHASE SYATEM
9. WHAT ARE COMPONENTS ?
Defination:
The least number of independent chemical
constituents in terms of which compostion of
every phase can be expressed by means of a
chemical equation
10. RULES FOR FINDING A COMPONENT:
Chemical formula representing the composition of a phase
is written on LHS.
Rest of chemical constituents that are represented in
chemical equation are written on RHS.
If quantities on RHS are made minus or zero then we get
compostion of phase on LHS.
11. NUMBER OF COMPONENTS IN A SYSTEM:
1-Component System:
Only 1 constituent forms the compostion.
Example :
Water
Suplhur
(ice) (water) (vapours)
12. 2-Component System:
When two components independently form a compostion then it is 2-
component System.
• Example:
(i) Mixture of two gasses like 02 and N2
Phase Component
Mixture of two = xO2 + yN2
Gases
(ii) Sodium Chloride Solution:
Phase Component
Aq. Sol of = xNaCl + yH2O
NaCl
13. (iii) Saturated Sol Of NaCl:
Phase Component
Aq.Sol of = xNaCl + yH20
NaCl
Solid NaCl = NaCl + 0H2O
(iv) Decomposition Of Calcium Carbonate:
Equation:
CaCO3 ⇌ CaO + CO2
(solid) (solid) (gas)
Phase Component
CaCO3 = CaO + CO2
CaO = 0CaCO3 + CaO
CO2 = CaCO3 – CaO
14. SATURATED SOLUTION OF NACL
Mixture of Aq. NaCl and Solid NaCl to form
saturated solution .That is a 2-Component System.
15. (v) Decomposition Of Ammonium Chloride:
Ammonium Chloride when heated in a closed vessel exisits in
equilibrium with the products of dissociation,ammonia and hydrogen
chloride gas.
Equation:
NH4Cl ⇌ NH3 + HCl
(solid) (gas) (gas)
Phase Components
Solid = NH4Cl
Gaseous = xNH3 + xHCl or NH4Cl
Thus dissociation of Ammonia is a 2-component system.
16. DEGREE OF FREEDOM :
The least number of variable factors
(concentration,temperature,pressure) which
must be specified so that the remaining
variables are fixed automatically and the
system is completely defined.
17. F=0 Non variant.
F=1 Univariant.
F=2 Bivariant.
A system is defined completely when it retain
the same same state of equilibrium with the
specified variables.
18. For a pure gas F=2 :
a system containing a pure gas has two
degree of freedom.
For a mixture of gases F=3:
a mixture of gases has 3 degree of
freedom (F=3)
For water ⇌ water vapours, F=1:
the system containing water has 1
degree of freedom.
19. For saturated NaCl Sol, F=1
NaCl ⇌ NaCl-Solution ⇌ water vapours
the system has 1 degree of Freedom .
For ice-water -vapour System:
ice ⇌ water ⇌ vapours.
It has no degree of freedom so F=0
20. DERIVATION OF THE PHASE RULE
The states of a system will depend upon a
temperature and pressure and these
variables are always there .
The concentration,however,depend upon the
number of phases.
The total number of variable of the system:
[P(C-1)+2]
21. Thermodynamic Equilibrium:
when a system is in equilibrium the partial
molal free energy of each constituentsof a
phase is equal to the partialmolal free
energy of the same constituents in every
phase.
F=No. of variables – No. of Equations
= [P(C-1)+2] – [C(P-1)]
= PC-P+2-PC+C
F= C-P+2
22. PHASE DIAGRAM
Plot showing the conditions of the pressure
and temperature under which two or more
physical states can exist together in a state
of dynamic equilbrium.
23. CHARACTERISTIC FEATURES:
1. Region or Areas:
Devided into solid liquid and gases.
2. Lines or Cures.
That separates two phases
3. Triple Point.
A triple point shows the conditions under which
all the three phases(solids liquid vapours) can
coexist in equilibrium.
