just keep some basic in mind, its give u enough information about this topic.

1. PHASE RULE
Prof. H. K. Khaira
Professor in MSME Deptt.
MANIT, Bhopal

2. The Phase Diagram
• Phase diagram: shows the regions of
pressure and temperature at which its
various phases are thermodynamically
stable.
• Phase boundary: a boundary between
regions, shows the values of P and T at
which two phases coexist in equilibrium.

4. The Gibbs Phase Rule
• The phase rule is
f=c–p+2
Where
f = degrees of freedom
c = number of components
p = number of phases
at equilibrium for a system of any composition.

5. The Gibbs Phase Rule
• Degree of freedom (f): It is the number of external
variables that can be changed independently
without disturbing the number of phases in
equilibrium. These are pressure, temperature and
composition.
• Component: a chemically independent constituent
of a system
• number of components (c): the minimum number
of independent species necessary to define the
composition of all the phase present in the system
• Phase: a state of matter that is uniform throughout
in chemical composition and physical state.

6. The Phase Rule
• Number of phase (p):
– Gas or gaseous mixture – single phase
– Liquid – one, two and three phases
• two totally miscible liquids – single phase
• a slurry of ice and water – two phases
– Solid
• a crystal is a single phase
• an alloy of two metals – two phases (immiscible)
• one phase (miscible)

7. Chapter 7
The Phase Rule
(a)
(b)
The difference between (a) a single-phase solution, in which the
composition is uniform on a microscopic scale, and (b) a
dispersion containing two phases, in which regions of one
component are embedded in a matrix of a second component.
7

8. Examples of Two Phases

10. H2O phase diagram: P — T
D
218 atm
C
Y
P / 10 5 Pa
I
solid
liquid
Line
S
Point
1 atm
Region
R
0.00611
gas
A
O
0.0024 0.01
T3
Tf
99.974
Tb
374.2
t/℃
10

11. H2O phase diagram: P — T
Region (s, l, g):
D
P / 10 5 Pa
218 atm
C
f=2, one phase
Y
I
solid
Line (OA, AD, AC):
liquid
S
f=1, two phases in
equilibrium
1 atm
R
0.00611
gas
A
Point (A):
O
0.0024 0.01
T3
Tf
99.974
Tb
t/℃
374.2
Tc
f=0, three phases in
equilibrium
11

12. Simple Example

13. Chapter 7
Physical Chemistry
One-component phase equilibrium
Hence, for a one-component system (pure water)
f＝1－p＋2＝3－p，(C＝1）
f ≥0, p ≥1, 3≥p≥1
p＝1，f＝2
p＝2，f＝1
p＝3，f＝0
13

14. Phase Rule in Metallurgical Systems
• But in case of metallurgical systems, the
pressure is kept constant.
• Hence the Phase Rule gets modified to
F=C–P+1