This document provides an overview of key concepts in thermodynamics taught by Professor Yash B. Parikh. It defines homogeneous and heterogeneous systems, pure substances, dimensions and units (including the SI system), various types of energy (internal, external, chemical, atomic, molecular), intensive and extensive properties, specific properties, states of a system, equilibrium, processes and cycles (including quasi-static processes and iso- processes where a property remains constant like isothermal, isobaric, isometric).

1. Unit No:01
Thermodynamics
Prof. Yash B. Parikh
M.Tech (Computer Integrated Manufacturing)
B.E.(Mechanical Engineering)
Assistant Professor
Department of Mechanical Engineering

2. Homogeneous & Heterogeneous Systems
2
Homogeneous system: - if a system consists of
homogeneous matter
throughout in chemical
composition & physical
structure.
e.g. ice, water, superheated steam, tea
Heterogeneous system: - if a system consists of matter
of different chemical
composition & physical
structure.
e.g. mixture of ice & water, mixture of two or more
non-miscible liquids (petrol & water)

3. Pure Substance
3
 It has a homogeneous & invariable chemical
composition even though there is a change of phase.
e.g. liquid water, mixture of water & steam.

4. Dimensions & Units
4
 Any physical quantity can be characterized by
dimensions.
 Dimension is defined as a measurable quantity.
 The magnitudes assigned to the dimensions are
called as units.
 Some basic dimensions such as mass m, length L,
time t , and temperature T are selected as Primary or
Fundamental dimensions.
 Whereas, velocity V, energy E, and volume v , are
selected as Secondary or Derived dimensions.

5. Units
5
 No of unit systems have been developed over the years.
1. English system : (United States Customary System)
It has no apparent systematic numerical base.
Various units are related to each other arbitrarily.
e.g. 12 in = 1 ft, 1 mile = 5280 ft , 4qt = 1 gal, etc.
In U.S. it’s still acceptable.
2. SI system : (International System) (Metric System)
It’s a simple & logical system based on a decimal
relationship between various units.
e.g. mm, cm, m, km, etc
It’s used in most of the nations for scientific &
engineering work.

6. Energy
6
 Energy is capacity to produce an effect, especially that
of change in motion of bodies.
Internal Energy :
Present in a system due to molecular motion,
arrangement of atomic structure, & it’s chemical
composition.
Various types of internal energies are :
a) Chemical Energy : released due to change in chemical
composition.
b) Atomic Energy : released due to change in atomic
structure of matter such as nuclear
fusion or fission.
c) Molecular Internal Energy : energy due to molecular
motion.

7. External Energy
7
a) Potential Energy : energy of position of mass w.r.t.
earth.
b) Kinetic Energy : energy arising due to motion of the
mass.
Total Energy = Internal Energy + External Energy

8. Properties of a System
8
 Any characteristic of a system is called a property.
 Pressure, volume, temperature, mass are few known
properties whereas viscosity, electrical resistivity are
less familiar.
 Properties are of two types,
1. Intensive : independent of the mass of the system.
e.g. temp, pressure, density.
2. Extensive : value depends on the size of the system.
e.g. length, volume, all forms of energies.
 An easy way to determine whether a property is
intensive or extensive is to divide the system into two
equal parts with a an imaginary partition.

9. Properties of a System
9
Each part will have same value
of intensive properties whereas
half value of extensive
properties.

10. Specific Properties
10
 Extensive properties per unit mass are called as
specific properties.
e.g. specific volume = volume/mass
specific total energy = total energy/mass

11. State of a System
11
 A set of properties that completely describes the
condition of the system is known as State.
 At a given state, all properties of a system have fixed
values.
 If the value of even one property changes, the state
will change to a different one.

12. Equilibrium
12
 Thermodynamics deals with the equilibrium states.
 Word equilibrium means state of balance.
 In an equilibrium state there are no unbalanced
potentials within the system.
 Types of equilibrium :
1. Thermal equilibrium – (if temp is same)
2. Mechanical equilibrium – (if press is same)
3. Chemical equilibrium – (if chemical compo is same )

13. Processes & Cycles
13
 Any change that system undergoes from one
equilibrium state to another is called a process.
 The series of states through which a system passes
during a process is called the path of the process.
 To describe a process completely, one requires,
- Initial & final states of the process
- Path it follows

14. Processes & Cycles
14
 When a process proceeds in a manner that the
system remains infinitesimally close to an equilibrium
state, it’s called as a quasi-static process.
 It’s a sufficiently slow process. (Allows the system to
adjust itself internally)
 Quasi-static process is an idealized process.
Note : -
We are interested in this process because,
1. Easy to analyze
2. Work – producing devices deliver most work when
they operate on it.

15. Processes & Cycles
15
 The prefix iso- is often used to designate a process
for which particular property remains constant.
 An isothermal process, is a process during which
temperature T remains constant.
 Similarly isobaric process (P const) & isometric
process (Specific V Const).