thermodynamics

1. THERMODYNAMICS OF PHASE
TRANSITIONS

2. Plan of talk
1)Definitions of
Phase
Phase transition
Phase Diagram
2)Types of phase transition
• First order phase transition
• Second order phase transition
a) Sublimation line
b) Melting line
c) condensation line

3. Phase
• Phase is defined as a system which is
homogeneous and has a definite boundary ,
it may be chemically pure substance or may
contain more than one component as in the
case of air or a mixture of two miscible liquids.
Phase transition
• It is a process in which a thermodynamic
system undergoes changes from one state to
another with different physical properties.

4. Phase Diagram
For a given set of independent variables,the
phases that are realized in nature are those
with the lowest free energy. The Gibbs free
energy is a function of T,P& N. At constant
temperature and pressure, Gibbs free energy
is proportional to the number of particles, i.e.
G(T,P, N)=Ng(T,P)

5. Phase transitions of first and second
order
First order:
1) G(T, P) continuous;
2) and discontinuous;
3) Ǝ latent heat

6. Concept of phase
P-T diagram for water

7. Second order
1) G(T, P) continuous;
2) S(T, P) and V(T, P) continuous;
3) response functions (susceptibilities)
discontinuous:

8. Second order
• The first derivative of Gibb’s free energy are
continuous but its second derivative shows
discontinuous change as a substance passes
from one phase to another.
The three coexistence lines are:
1) Sublimation line
2) Melting line
3) condensation line

9. 1)Sublimation line
• Here the solid coexists with the gas.

10. 2) Melting line
Its also called fusion line.
Here the solid coexists
with the liquid.
Second order phase
transitions are usually
associated with the
abrupt changes in the
various properties
characterizing the
symmetry of a body.

11. 3) Condensation line
Its also called the
vapour pressure line.
Here the gas coexists
with the liquid. The
line begins at the
triple point and ends
at the critical point C.