This document provides an overview of phase equilibria and phase diagrams. It defines key terms like phase, phase equilibrium, degrees of freedom, and the phase rule. It describes one-component systems and how the number of phases changes with temperature. It also discusses liquid mixtures and whether they are miscible, partially miscible, or immiscible. Other topics covered include condensed phases, eutectic systems, solid solutions, simple three-component systems, and different types of distillation processes.

1. Phase Equilibria
Group 03
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2. Table of
CONTENTS
1. Introduction
2. One component system
3. Miscible, partially miscible & immiscible liquid
mixtures
4. Condensed phase
5. Eutectic systems and compounds formation
6. Solid solutions
7. Simple three component systems
8. Distillation of liquid mixtures
(Congruent and non-congruent)
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3. INTRODUCTION
What is Phase?
Any part of a system which is physically
separated from other part of the system by
a distinct boundary.
A phase can be a;
Solid, Liquid, Vapor (gas) or aqueous.
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4. What is Phase Equilibrium?
• Thermodynamic Definition
A system is at equilibrium if it’s free
energy is at a minimum.
• Characteristics of the system do not
change with time, the system is stable.
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5. Phase Equilibrium
Phase equilibrium is the study of the equilibrium
which exists between or within different states of
matter namely solid, liquid and gas. Equilibrium is
defined as a stage when chemical potential of any
component present in the system stays steady
With time.
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6. Phase Rule
This rule is very useful to understand the effect of intensive
variables, such as temperature, pressure as well as
between chemical constituents.
The phase rule is stated as;
F - Number of degrees of freedom
C - Number of components
P – Number of phases
F = C – P + 2
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7. Degrees of freedom (F)
Is the least number of intensive variables
that must be fixed/known to describe the
system completely.
Intensive variables are:
- Temperature, pressure, concentration.
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8. Number of Component is defined as
the smallest number of
independently variable constituents,
by means of which the composition
of each phase can be expressed in
the form of a chemical equation.
Number of Components (C)
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9. One component system is a system involving one pure
chemical.
Ex: At freezing point of water, three phases are in equilibrium.
Ice(s) Water (aq) Water vapor(g)
The chemical composition of all the phases is H2O ,
it is one component system.
One Components System
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10. One component system mean , C=1,
From phase rule,
F = C – P + 2
F = 1 – P +2
F = 3 – P
Degree of freedom is depend on the number of phases present
at equilibrium.
Three different cases are possible;
• P=1, F=2 ( Bivariant system)
• P=2, F=1 (Univariant System)
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11. Miscibility
Miscibility means how completely two or more liquids dissolve in
each other. It is a qualitative rather than quantitative observation,
• Miscible
• Partially miscible
• Immiscible
Miscibility depend on the force of the attraction between the
molecules of the different liquids. 11

12. Miscible
The ability of liquid to completely dissolve in
another liquid solution . A distinct layer between
two liquid will not form I this type of solutions.
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13. Partially Miscible
• A liquid is partially miscible in another liquid if,
when mixed, the two liquids makes (liquid)
phases that contain some fraction of each liquid in
each phase.
• Partially miscible refers to those liquids which are
partially soluble in each other.
e.g. : Water and Triethylamine solution
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14. Immiscible Liquid Mixture
• Immiscible liquids are liquids which are completely
insoluble in each other.
• Immiscibility is the property where two substances are not
capable of combining to form a homogeneous mixture.
• Components of an immiscible mixture will separate from
each other.
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15. Condensed Phases
Condensed phase of matter are two ; Solid and
Liquids. These phases of matter are said to be
condensed phases .
Because the inter-molecular phases are fairly
strong as compared to those in gases.
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16. ● In two component system there
are four possible phases solid
Ag, solid Pb, solution of Ag, + Pb
and vapour.
● Since the pressure has no effect
on equilibrium so the system can
be represented by temperature
concentration diagram at
constant atmospheric pressure.
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17. Eutectic System
(Eutectic comes a Greek word EUTEKTOS)
A binary system in which two or more components are miscible in all
proportions in the liquid state, but do not react chemically and each
component has the property of lowering each others melting point is
known as eutectic (easy to melt) system.
A eutectic system only forms when there is a specific ratio between
the components.
Example:
• Sodium chloride and water; The system is used to make ice cream
and to melt ice and snow.
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18. Eutectic – Easy to melt. Consider a binary system
in which two components are miscible
in all proportions in the liquid (molten)
state. They do not react chemically and
each component has the property of
lowering each other’s freezing point. Such
a binary system is called Eutectic System.
A eutectic system is a homogeneous(A system consists of one
phase only) solid mixture.
● A eutectic system only forms when there is specific ratio
between the components.
● That has lower solidification point.
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19. Examples of Eutectic Systems
Several examples of eutectic systems or eutectoids
exist, both in metallurgy and involving nonmetallic
components:
•NaCl and H2O form a eutectoid when the mixture is
23.3% salts by mass with a eutectic point at 21.2 0C.
The system is used to make ice cream and melt ice
and snow.
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20. The minimum freezing point
attainable corresponding to the
eutectic mixture is known
as “Eutectic Point”
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21. Solid Solution
What is Solvent and Solute…
Solvent : the component of a solution that is present in
the greatest amount. It is the substance in which the
solute is dissolve.
Ex: the solvent for seawater is water
the solvent for air is nitrogen
Solute : the substance that is dissolved in a solution. For
solution of fluid the solvent is present greater then solute.
Ex: salt in water
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22. What is a solid Solution
 When in a solid, the atoms of solute are
present in the lattice of the solvent, it is
known as solid solution.
A solid solution is basically a crystalline phase that can
have variable composition.
often, it have certain properties of material
eg: conductivity, ferromagentism
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23. Type of Solid Solution
The solid solution can be of two types.
1. Substitution solid solution
i. Disordered
ii.Ordered
2. Interstitutional solid solution
Examples:
•Al2O3 – Cr2O3 (substitutional, complete)
•Si - Ge (substitutional, complete)
•Fe - C (interstitial, partial)
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24. Substitutional Solid Solution
One type of atoms for another so that
solute(Cu) enter the crystal to take positions
normally occupied by solvent atoms (Ni).
The great majority of the solid solution are substitutional
type.
Ex: Cu-Ni , Cd-Mg.
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25. Disordered Substitutional Solid Solution
Solute atoms do not occupy specific position
random in the lattice structure of the solvent, it
is known as disordered solid solution.
Most of the solid solutions are disordered solid
solution.
Ex: Alloy
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26. Ordered Substituional Solid Solution
If the atoms of the solute occupy certain
preferred sites in the lattice of the solvent, an
ordered solid solution is formed. It may ocure
only at certain fixed ratios of the solute atoms.
The alloy in the disordered condition, if in I cooled slowly,
under –goes a re-arrange meant of the atoms because of
the diffusion that takes place during cooling.
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27. Interstitial Solid Solution
When the atoms of the solute occupy the
interstitial space in the lattice of the solvent, it is
known as interstitial solid solution.
• This type of reaction occurs when the solute atom is
equal to or the slightly smaller than the solvent atom.
• More common for C,N,O and H as solutes.
• More easily dissolved in transition metal solvent .
• Solubility is limited.
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28. Ex: An example of interstitial solid
solution is C in iron
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29. Simple Three Component Systems
In systems containing three components but only one
phase, F = 3 - 1 + 2 = 4 for a noncondensed system.
• The 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.
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30. Use of The Three Component System
• Because we are dealing with a three-
component system, it is more convenient to
use triangular coordinate graphs,
• several areas of pharmaceutical processing
such as crystallization, salt form selection, and
chromatographic analyses rely on the use of
ternary systems for optimization.
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31. Distillation
● Distillation is a process in which the components of a
substance or liquid mixture are separated by heating it to a
certain temperature and condensing the resulting vapor.
● Distillation is based on the different boiling points or volatility
values of the components and it is a physical process.
● Types of distillation include simple distillation, fractional
distillation, vacuum distillation and so on.
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32. Simple Distillation
Simple distillation may be
used when the boiling points
of two liquids are
significantly different from
each other or to separate
liquids from solids or non-
volatile components.
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33. ● In simple distillation the only one chain of
vaporization and condensation takes place.
● Its only applicable if difference of boiling points
is very large like 25-35 0C.
● This is the sequence of events in distillation:
heating → evaporating → cooling → condensing
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34. Fractional Distillation
• This method of distillation is used to separate two (or more)
miscible liquids.
• A fractionating column is used to separate the components.
● This is a another common type of distillation.
● It is used to separate liquids having very close boiling points.
● It requires more evaporation/condensation cycles.
● For fractional distillation one fractionating column is introduced
between flask and condenser. Each gap works as one cycle.
● It is use to petro chemical industry.
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35. 35

36. Vacuum Distillation
• Vacuum distillation is used to separate components
that have high boiling points.
• This method of distillation is particularly useful when
the normal boiling point exceeds the decomposition
temperature of a compound.
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37. Use Of Distillation
• Purification of alcohol
• Crude oil refining
• Making liquefied gases from air
Ex: Nitrogen, Oxygen, and Argon are distilled from air.
• Distillation is used for many commercial processes, such as
the production of gasoline, paraffin, distilled water and
many other liquids.
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38. RESOURCES
• Atkins, Peter.Paula,julio de; keeler ,James(2018)
.Atkins’ Physical chemistry (11th edition) oxford
university press. Pp 123 – 125 , ISBN 9780198769866.
• https://www.wattco.com/casestudy/phase-equllibrium/
• https://www.springer.com/referenceworkentry/10.1007
%2F1-4020-4496-8_252/
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39. THANK
YOU
Any Questions ?
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40. T.D.Jayawickrama 16APP2648
K.A.H. Navodya 16APP2666
W.S.H.Fernando 16APP2679
M.P.P.Chethiya 16APP2642
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