PHASE RULE INTRODUCTION PHASE COMPONENTS DEGREE OF FREEDOM GIBBS PHASE RULE TWO COMPONENT SYSTEM SLIDESHARE

1. Phase rule
CECH - 509
UNIT - 4 (B)
BY – Ms MAYURI R SOMPURA
HJD INSTITUTE – KUTCH
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2. PHASE :-
• A phase - is derived as any homogeneous and physically distinct part
or a system which bounded by a surface and is mechanically seperable
from other part of the system.
Example :
1. A gas mixture constitutes a single phase since gases are completely
miscible.
2. Immiscible liquids constitute different phases.
Carbon tetrachloride and water – 2 phases
3. Completely miscible liquids form single phase.
Water and alcohol – 1 phase
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3. PHASE :-
• Decomposition of calcium carbonate – 3 phase system
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4. Components :-
• The number of component - of a system at equilibrium is derived as
the smallest no of independently variable constituents by means of
which the composition or phase can be expressed either directly or in
terms of chemical equation.
Example :-
1. Water exists in three phase but its composition is same – 1
component system
2. Aqueous sucrose solution – 2 component, 1 phase
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5. Components :-
For a chemically reactive system, the number of components is given
by :
C = N – E
Where,
N = no. of chemical species
E = no of independent equation relating the concentration of N
species
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6. Degree of freedom :-
Degree of freedom – no. of independent variables such as temperature,
pressure and concentration which must be specified in order to define
system completely.
Example :-
1. 1 component system having 2 phases
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7. Willard Gibbs in 1870.
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8. 1. Greater the number of components in a system, greater is number of
degree of freedom for a given number of gases.
2. Greater the no. of phases – smaller no. of degree of freedom
3. For a given no. of components, the no. of phases is maximum when
the no of degree of freedom is zero.
Thus,
 For 1 component system – Maximum phases is 3
For 2 component system – Maximum phases is 4
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9. For two component system:-
• For a two component system,the phase rule becomes :-
F = C – P + 2
F = 2 – P + 2
F = 4 – P
• Minimum no. of phase in any system is 1.
• Maximum no. of degree of freedom is 3.
• Thus, three variables are necessary to describe a system.
• Since it is difficult to graph three variables, lets say pressure isconstant
on a diagram of temperature v/s concentration.
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10. For two component system:-
• This reduces the degree of freedom of the system by 1.
• Therefore, phase rule equation will be :-
F = 3 – P
This is known as reduced phase rule equation.
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11. For two component system – solid-liquid
equilibrium:-
Case – 1 :-
• Two components are not miscible in solid state and form a eutectic
mixture.
Eutectic mixture - when two solids having maximum freezing point,
solidifies together, this solid mixture is known as
eutectic mixture.
Case-2 :-
• Two compounds form a stable compound with a congruent melting
point.
by - Ms MAYURI R SOMPURA 11