This document discusses thermodynamic equilibrium, states, and phases. It defines thermodynamic equilibrium as a state where a system achieves thermal, chemical, and mechanical balance, with nothing changing at the macroscale. Thermal equilibrium occurs when two objects have the same temperature, and chemical equilibrium is a state where reactants and products are present at constant concentrations. A system's state is defined by variables like temperature, pressure, and volume, and a phase is a physically distinct, chemically homogeneous portion of a system. The phase rule relates the number of degrees of freedom in a system to the number of components and phases present.

1. Thermodynamic Equilibrium,
State & Phase
GUIDED BY-: PROFESSOR RATHODE SIR
By-
1) Aditya Gohad (TCH57)
2) Dharmraj (TCH56)
3) Abhay (TCH..)

2. Content
1) Introduction
2) Thermal Equilibrium
3) Chemical Equilibrium
4) Mechanical equilibrium
5) State of System.
6) State with respect Mechanical equilibrium
7) Phase of System.
8) Application of Phase
9) Limitation of Phase

3.  THERMODYNAMIC EQUILIBRIUM:
Introduction
Thermodynamics is the branch of science which basically
deals with the transformation of energy i.e. conversion of energy
from one form to other.
The system is said to be in thermodynamic equilibrium when
the system achieves the chemical, thermal & mechanical
equilibrium .
Equilibrium implies balance of (generalized) forces.

4.  Under equilibrium conditions nothing changes at the
macroscopic scale, but this does not mean than
nothing is happening at the microscopic scale.
Thermal Equilibrium
Chemical Equilibrium
Mechanical Equilibrium

5. Thermal Equilibrium:
1)The zero th law of Thermodynamics explain basic thermal equilibrium.
2) It states that if body A is in thermal equilibrium with B and body B is in
thermal equilibrium with body C then A is in thermal equilibrium with C.
3)Thermodynamic equilibrium leads to the large scale definition
of temperature. When two objects are in thermal equilibrium they are
said to have the same temperature .

6. Chemical Equilibrium:
1)In a chemical reaction, chemical equilibrium is the state in
which both reactants and products are present in concentrations
which have no further tendency to change with time, so that there
is no observable change in the properties of the system.
2) Let’s consider,
α A + β B ⇌ σ S + η T
then according to chemical equilibrium,
K1(A)α (B)β = K2 (S)σ (T)η

7. Mechanical Equilibrium:
Let us start with a simple mechanical system (it is easier to
visualize mechanical systems)
1) A rectangular block (Figure in next slide) (under an uniform
gravitational potential).
2)The potential energy (PE) of the system depends on the
height of the centre of gravity (CG).
3)The system has higher PE when it rests on face-A, than when
it rests on face-B. The PE of the system increases when one
tilts it from C1 → C2 configuration. This increase in potential
energy is the ‘activation energy’ required.
4)In configurations such as C1,C2 & C3 the system will be in
equilibrium (i.e. will not change its configuration if there are
no tilt).

8. Mechanical Equilibrium of a Rectangular Block
Centre
Of
Gravity
otential
Energy
=
f(height
of
CG)
Metastable state
Unstable
Stable
Configuration 
Lowest CG of all possible
states
C1 C3
C2
 We start by considering the mechanical equilibrium of a block- this is to get a first feel- additional concepts will be
required when dealing with condensed matter systems.
C1
C2
C3
Activation
barrier

9. State:
1)For thermodynamics a thermodynamic state of a system is
its condition at a specific time, that is fully identified by
values of a suitable set of parameters known as state
variables, state parameters or thermodynamic variables.
2) Once such a set of values of thermodynamic variables has
been specified for a system, the values of all thermodynamic
properties of the system are uniquely determined.
3)The set of condition that specify all the properties or
describe the system is called the thermodynamic state of that
system.

10. For example the thermodynamic state
could include:
1) The temperature of system.
2) The pressure of system.
3) The volume of system.
4) The number of moles of
system.

11. State with respect to mechanical equilibrium:
If the system changes its state after small perturbations(tilt)
then the system
→ is in an unstable state
If the system returns to its original state after a small
perturbation (tilt) then the system
→ is in a stable or metastable state (lies in an energy
minimum)
If the system returns to its original position after small
perturbations but does not do so for large perturbations then
the system
→ is in a metastable state (not in the global energy
minimum)

12. Phase:
1)A phase can be defined as a physically distinct and
chemically homogeneous portion of a system that has a particular
chemical composition and structure.
2)According to phase rule:
The number of degrees of freedom, F (no. of independently
variable factors), number of components, C, and number of phases in
equilibrium, P, are related as
F = C – P + 2
3)Number of external factors = 2 (pressure and temperature).
For metallurgical system pressure has no appreciable effect on
phase equilibrium and hence,
F = C – P + 1

13. Applications of Phase Rule
1. The most imp applications of phase rule are for
metallurgists. Phase diagram predicts the temp
&composition at which metal can be separated from their ore
& give an idea about the purity of metal.
2. The phase diagram gives the existence of different phases
of metal along with specific temperature & composition of
alloying metal. This helps in designing an alloy that can be
used for specific application.
3. It has an imp application in environmental engineering,
with help of phase diagram for a particular gaseous
pollutant, one can predict at what temp & pressure condition
the pollutant will be solidify.

14. Limitations of Phase Rule.
1. It is difficult to apply the system which reach the
equilibrium slowly.
2. This rule does not consider the influence of other forces
such as gravitational, magnetic & electrical on the
equilibrium.
3. The quantities of phases are not taken into account.

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