The document discusses different types of compound formations including compounds with congruent and incongruent melting points. It defines key terms like phase, component, degree of freedom, and explains concepts like the phase rule and how it relates the number of components, phases, and degrees of freedom in a system. Examples of systems forming compounds with congruent melting points like zinc-magnesium and systems forming compounds with incongruent melting points like picric acid-benzene are provided along with diagrams showing their phase diagrams.

2.  Introduction
 Formation of compound with congurent
melting point
 Formation of compound with incogurent
melting point

3.  Gibbs Phase Rule
 The Phase rule gives the relation between
the degree of freedom (F),the number of
components (C) and the number of phase
(P) present at equilibrium in a given system.
F= C-P+2
 Phase (P) : Any homogenous and physically
distinct part of a system which is a bounded
by a surface & is mechanically separable
from each other parts of a system.

4.  Component (C) : The smallest no, of
independently variable constituents by
means of which the composition of each
phase can express in terms of chemical
equation.
 Degree of freedom (F) : The minimum
number of variable factors such as
pressure,temprature and concentration
which must be specified in order to define
the system completely at equilibrium.

5. Solid- Gas system Solid-Liquid system
 Hydrate formation
 amino compound
formation
 Formation of
compound with
congurent melting
point
 Formation of
compound with
incogurent melting
point

6.  Defination :
 A compound melts completely into liquid
having the same composition as that of the
solid phase is said to possess a congurent
melting point.
 Let A and B are two components and AB a
solid component form by their combination.
 In this system there are three different solid
phases A,B and AB
 Freezing point curves AC,BE and CDE

7.  AC – Solid A is in equilibrium
with liquid phase
 BE- Solid B is in equilibrium
with liquid phase
 CDE- Solid component AB is in
equilibrium with liquid phase,
at different temperatures
 The curve AC is univariant as,
F=C-P+1 = 2-2+1 = 1
 The point C known as first
eutectic point of the system.
 The point C is thus non-
variant as
F=C-P+1 = 2-3+1 = 0

8.  Curve BE is univariant as, F=C-P+1=2-2+1=1
 The point E is known as the second eutectic point
of the system.
 The liquid consists of the curve AC,CDE & BE
whereas solidus consists of the curve FCG & HEJ,AF
& BJ.
 The maximum point D of the curve is the congurent
melting point accordingly to the phase rule, D is
non-variant.
 At certain temperature, the compound AB can have
two solubilities at same temperature i.e. X and X’
 The congurent melting point can be above,below or
in between the melting point of both the
components. The position of congurent melting
point gives the composition of the compound
formed.

9.  Curve BE represents depression in freezing point
of the compound AB on addition of B.
 Curve AC represents depression in freezing
point of the compound AB on addition of A.
 The congurent melting point can be
above,below or in between the melting point of
both the components. The position of congurent
melting point gives the composition of the
compound formed.
 Example :
 Zinc- magnessium system
 Aluminium-magnessium system
 Mercury – Thallium system
 Phenol- aniline system

10. Zinc- Magnessium
System
 Zinc – Magnessium
system of frmation of
compound with
congurent melting
point.

11.  In many system,the compound formed by
the combination formed of two
components,instead of melting
congurently,decompose when heated giving
a new solid phase and a solution of solid
with a composition different from that of
the solid phase.Such compound said to
have an incongurent melting point.
 Equation :
 S1 S2 + solution
Original solid New solid

12.  Let A & B be the two
component which
combine to form a
compound AB2
 Point A & B are
freezing points.
 Point C is eutectic
point of the system
which is non- variant
as solid A, solid AB2 &
liquid phase are
present in equilibrium.

13.  Curve AC : freezing point of A which indicates
lowering the freezing point of A when B is
added. It is fusion curve of A. it is univariant.
 Curve CD : fusion curve of compound AB2
system is univariant along CD
 Curve BD : fusion curve of B
system is univariant along BD

14.  If we cool a composition X, A is the first
solid to separate out at point X’
 On cooling composition Y, B is first solid to
separate out at point Y’
 At point D, transition reaction occurs
Solid AB + Solution Solid AB2
 The compound AB2 now stable. Curve CD
would have proceeded upto E.
 If the curve CD is prolonged further, we get
point D which would normally be the
congurent M.P. of the compound this point
is called a submerged maximum.

15.  Examples :
 Picric acid-benzene system
 Gold-antimony system
 Sodium sulphate- water system

16.  REFERENCES :
 Principles of Physical Chemistry – Puri.
Sharma.
 D.N. Bajpai, advanced physical
chemistry,s.chand 1st edition,1992
 Physical chemistry by Glasston page
no.175,176
 K.L. Kapoor,Elemental of physical
chemistry,page no.150,151.

17. Thank you…!