Post on 15-Apr-2017
transcript
Khalid T MaaroofMSc. Pharmaceutical sciences
School of pharmacy – Pharmaceutics department
1Online access: bit.ly/physicalpharmacy
Phase equilibria
Physical Pharmacy
10/31/2015
What was equilibrium?
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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
What is intensive variable???
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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….
Systems Containing One Component
This is the phase diagram for a typical pure substance.
at higher pressure, the melting temperature would be higher because the line between the solid and liquid areas slopes slightly forward.
Increasing pressure at constant temperature changes liquid to solid and vice versa
The same explanation for liquid vapour boundary
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 three phases are in equilibrium together
Normal melting and boiling points
The phase diagram for water In the case of water, the
melting point gets lower at higher pressures. Why?
Imagine lowering the pressure on liquid water along the line in the diagram below.
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Systems Containing more than one Component
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
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).
Upper and lower consulate temperatures
Two-Component Systems Containing Solid and Liquid Phases: Eutectic Mixtures
two components are completely miscible in the liquid state and completely immiscible as solids,
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
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.
Temperature and pressure are considered to be constant.
Triangular Diagram
Ternary Systems with One Pair of Partially Miscible Liquids
e.g. Water and benzene + alchohol
• Alchohol provide solvation
• binodal curve
Alterations of the binodal curves with changes in temperature.
Ternary Systems with Two Pairs of Partially Miscible Liquids
Ternary Systems with Three Pairs of Partially Miscible Liquids
F=0 Why???
Questions !
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