Phase Equilibrium
 A phase : a physically distinct portion of a system
that is separated from the other portion by a
boundary.
 A component : a chemically different constituents
that participates in the formation of phases.
Example:
Ice
cubes
water
Two Phases
One Component
Gibbs’ Phase Rule
• used
to determine the degree of freedom which is the least
number of independent variables, e.g.: temperature, pressure,
and concentration affecting various phases at equilibrium.
F=C –P+ 2
Where;
• F is the no. of degrees of freedom.
• C is the no. of components.
• P is the no. of phases exist in equilibrium.
 Solids are soluble in liquids , while liquids are
miscible in liquids.
 Types of miscibility:
miscible
Partially miscible
Ethyl alcohol /water
phenol / water
immiscible
mercury / water
Factors affecting miscibility of phenol in water:
1- Concentration
few drops
of phenol
Water rich
phase
few mls of
phenol
Phenol rich
phase
Water / phenol
One phase
water / phenol
Two phases
Factors affecting miscibility of phenol in water:
2- Temperature
Increase
temperature
Critical Soln.
Temperature
“upper consolute
temp.”
Determination of critical solution temperature
of phenol/ water system:
Tie the
Suspend
the
amp.
So with
thatIn
the
If
the difference
between
the
temp.the
Record
the
temperature
at
a
which
beaker
Heat
WB
gradually
ampoule Turn
with off the flame and record the
contents
of
the
ampoule
must
be
at
which
turbidity
disappears
and
turbidity
disappears
(T1)
put
using
water
continuous shaking
the ampa
a thread temperature
at whichofturbidity
completely
the
re-appears
isimmersed
> 2ºC, heatinto
again
and
thermometer
form
up
&
down
re-appears (T2)
water bath
record
the temp. at whichwater
turbidity
bath
disappears again.
Precautions :
1- Be very cautious with the ampoule (phenol injury is
3rd degree burn).
2- Suspended ampoule must not touch the wall or
bottom of the beaker.
3- when recording the temperature, the suspended
thermometer must not touch the wall or bottom of the
beaker.
4- If the difference between the temp. at which turbidity
disappears and re-appears is > 2ºC, heat again and
record the temp. at which turbidity disappears again.
Temperature (°C)
Ampoule
No.
% of
phenol
1
2
3
4
5
6
7
10
20
30
40
50
60
70
Turbidity
Turbidity
disappeared reappeared
( T1 )
(T2)
Average
Temp.
(T1+T2 ) / 2
Draw graph:
Critical solution temperature of phenol
misciblity temp. ◦C
80
70
60
50
40
30
20
10
0
0
10
20
30
40
50
conc. of phenol w/w
60
70
80
Exam
45
40
Temperature (ºC)
35
30
83%
25
20
15
10
5
16%
83%
0
0
20
40
60
% phenol (w/w)
80
100