Physicochemical Pharmaceutics

1. Physical Pharmacy
Phaseequilibria
Dr.L.T.M.Muungo,PhD
10/31/2015 1

2. What was equilibrium?
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3. 3

5. What is intensive variable???
Phase rule
Coexistence of phases can only occur over a limited
range.
phase rule is a relationship for determining the least
number of intensive variables that can be changed
without changing the equilibrium state of the system.
P is the number of phases present
F is termed the number of degrees of freedom
C in represents the number of components in the system
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6. The number of degrees of freedom: is the least
number of intensive variables that must be
fixed/known to describe the system completely.
Examples of intensive variables are: temperature,
pressure, concentration….
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7. Systems Containing One Component
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8. This is the phase diagram for a typical pure substance.
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9. at higher pressure, the melting temperature would be
higher because the line between the solid and liquid
areas slopes slightly forward.
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10. Increasing pressure at constant temperature
changes liquid to solid and vice versa

11. The same explanation for liquid vapour
boundary
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12. The point labelled as C in the phase diagrams is critical
temperature.
Note the process of
sublimation as shown on
the graph; below the point
T.
Point T is called triple
point.
Where all three lines meet,
you must have a unique
combination of temperature
and pressure where all
th1r
2ee phases are in

13. Normal melting and boiling points
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14. The phase diagram for water
In the case of water, the
ts lower at
s. Why?

15. 15

16. Imagine lowering the pressure on liquid
water along the line in the diagram below.
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17. Systems Containing more than one
Component
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18. CONDENSED SYSTEMS
a maximum of three degrees of freedom is possible in
a two-component system.
More components more degrees of freedom
In two component one phase system (maximum no of
variables) F = 2 – 1 + 2 = 3
E.g. temperature, pressure, and concentration
we frequently choose to disregard the vapor phase
and work under normal conditions of 1 atm pressure.
Now we can use planar figures instead of three
dimensional (this will be easier)
condensed systems: When we only consider solid
and liquid phases
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19. Two-Component Systems Containing Liquid
Phases
The maximum
temperature at which
the two-phase region
exists is termed the
critical solution or
(upper consolute
temperature).
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20. Upper and lower consulate temperatures
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21. Two-Component Systems Containing Solid
and Liquid Phases: Eutectic Mixtures
two components are completely miscible in the liquid
state and completely immiscible as solids,
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23. Eutectic composition
“contact melting”: lowest melting temperature over
a composition range.
eutectic composition is the composition of two or
more compounds that exhibits a melting temperature
lower than that of any other mixture of the
compounds
The primary criterion for eutectic formation is the
mutual solubility of the components in the liquid or
melt phase.
Lidocaine and prilocaine, two local anesthetic
agents, form a 1:1 mixture having a eutectic
temperature of 18◦C
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24. Phase Equilibria in Three-Component Systems
In systems containing three components but only one
phase.
four degrees of freedom are temperature, pressure,
and the concentrations of two of the three
components.
Only two concentration terms are required because the
sum of these subtracted from the total will give the
concentration of the third component.
T
2
e
4
mperature and pressure are considered to be

25. Triangular
Diagram
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26. Ternary Systems with One Pair of Partially Miscible
Liquids
e.g. Water and
benzene + alchohol
• Alchohol provide
solvation
• binodal curve
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27. Alterations of the binodal curves with
changes in temperature.
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28. Ternary Systems with Two Pairs of Partially
Miscible Liquids
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29. Ternary Systems with Three Pairs of Partially
Miscible Liquids
F=0 Why???
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30. Questions !
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