This chapter is basically focused on entropy and its relations with other thermodynamic parameters.

1. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
ENTROPY
Prof. Aniket Suryawanshi
Asst. Prof. Automobile Engg. Dept.
R. I. T. Rajaramnagar

2. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
OUTLINE OF CHAPTER
Clausius’ Inequality.
Entropy: A property of system.
Entropy of pure substances.
Increase of entropy principle.
Entropy changes in flow processes or open systems.
Entropy changes in non flow process or closed systems.
Entropy generation.

3. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
Entropy (S) = a measure of randomness or disorder
MATTER IS ENERGY.
ENERGY IS INFORMATION.
EVERYTHING IS INFORMATION.
PHYSICS SAYS THAT
STRUCTURES... BUILDINGS,
SOCIETIES, IDEOLOGIES...
WILL SEEK THEIR POINT OF
LEAST ENERGY.
THIS MEANS THAT
THINGS FALL.
THEY FALL FROM HEIGHTS
OF ENERGY AND STRUCTURED
INFORMATION INTO
MEANINGLESS, POWERLESS
DISORDER.
THIS IS CALLED
ENTROPY.
ENTROPY AND DISORDER

4. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
In any spontaneous process, the entropy of the
universe increases.
ΔSuniverse > 0
Another version of the 2nd Law:
Energy spontaneously spreads out if it has no outside
resistance
Entropy measures the spontaneous dispersal of energy as a
function of temperature
How much energy is spread out
How widely spread out it becomes
Entropy change = “energy dispersed”/T
SECOND LAW OF THERMODYNAMICS
occurs without outside intervention


5. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
One property common to
spontaneous processes is that
the final state is more
DISORDERED or RANDOM
than the original.
Spontaneity is related to an
increase in randomness.
The thermodynamic property
related to randomness is
ENTROPY, S. Reaction of K
with water
ENTROPY

6. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
How probable is it that reactant
molecules will react?
PROBABILITY suggests that a
spontaneous reaction will result in
the dispersal
* of energy
* or of matter
* or of energy & matter.
Directionality of Reactions

7. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
Entropy of the Universe
ΔSuniverse = ΔSsystem + ΔSsurroundings
Positional disorder Energetic disorder
ΔSuniverse > 0  spontaneous process
Both ΔSsys and ΔSsurr positive
Both ΔSsys and ΔSsurr negative
ΔSsys negative, ΔSsurr positive
ΔSsys positive, ΔSsurr negative
spontaneous process.
nonspontaneous process.
depends
depends
ENTROPY OF THE UNIVERSE

8. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
ENTROPY OF THE SURROUNDINGS
System
Heat Entropy
Surroundings
System
Heat Entropy
Surroundings
T
ΔH
ΔS
sys
surr 
Low T  large entropy change (surroundings)
High T  small entropy change (surroundings)
ΔHsys < 0
ΔHsys > 0
ΔSsurr > 0
ΔSsurr < 0
(Energetic Disorder)

9. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
POSITIONAL DISORDER AND PROBABILITY
Probability of 1 particle in left bulb = ½
" 2 particles both in left bulb = (½)(½) = ¼
" 3 particles all in left bulb = (½)(½)(½) = 1/8
" 4 " all " = (½)(½)(½)(½) = 1/16
" 10 " all " = (½)10 = 1/1024
" 20 " all " = (½)20 = 1/1048576
" a mole of" all " = (½)6.021023
The arrangement with the greatest entropy is the one with the
highest probability (most “spread out”).

10. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
Ssolid < Sliquid << Sgas
ENTROPY OF THE SYSTEM: POSITIONAL DISORDER
Ludwig Boltzmann
Ordered
states
Disordered
states
Low probability
(few ways)
High probability
(many ways)
Low S
High S
Ssystem  Positional disorder
S increases with increasing # of possible positions

11. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
Entropy usually increases when a pure
liquid or solid dissolves in a solvent.

12. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
ENTROPY CURVE
Solid GasLiquid
S
(qrev/T)
(J/K)
Temperature (K)
0
0
 fusion
 vaporization
S° (absolute entropy) can be calculated for any substance

13. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
S increases slightly
with T
S increases a large
amount with phase
changes
ENTROPY CURVE

14. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
Entropy Increases with...
• Melting (fusion) Sliquid > Ssolid
ΔHfusion/Tfusion = ΔSfusion
• Vaporization Sgas > Sliquid
ΔHvaporization/Tvaporization = ΔSvaporization
• Increasing ngas in a reaction
• Heating ST2 > ST1 if T2 > T1
• Dissolving (usually) Ssolution > (Ssolvent + Ssolute)
• Molecular complexity more bonds, more entropy
• Atomic complexity more e-, protons, neutrons

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RECAP: CHARACTERISTICS OF ENTROPY
• S is a state function
• S is extensive (more stuff, more entropy)
• At 0 K, S = 0 (we can know absolute entropy)
• S > 0 for elements and compounds in their standard states
• ΔS°rxn = nS°products - nS°reactants
• Raise T  increase S
• Increase ngas  increase S
• More complex systems  larger S

16. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
Volume
Pressure
•
•
a
b
•
d
T1
Q1
Q2
V
nRT
P 1
=

V
const
P
.
=
T2
•
c
Q=
0
Q=
0
V
nRT
P 2
=
CLAUSIUS THEOREM
Clausius Theorem:
It states that “ a reversible line can be replaced by
two reversible adiabatic line and a reversible isothermal line.”

17. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
This Proves that;
Violation of Kelvin – Planck Statement results in violation of Clausius Statement.
Converse is also True.
SECOND LAW OF THERMODYNAMICS
TH
Wrev.
QH
QL1
Reversible
Heat
Engine
Irreversible
Heat Engine
TL
QL2
W irrev.

18. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
AVAILABILITY
ENERGY:

19. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
AVAILABILITY
HIGH GRADE ENERGY:
Energy that can be completely transformed into work without any loss.
i.e. fully utilizable.
Examples of High Grade Energy:
1. Mechanical work
2. Electrical work
3. Water power
4. Wind power
5. Tidal power

20. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
AVAILABILITY
LOW GRADE ENERGY:
Energy of which only a certain portion can be converted into mechanical
work is called low grade energy.
Examples of Low Grade Energy:
1. Heat and Thermal Energy
2. Heat derived from combustion of fossil fuels
3. Heat derived from nuclear fission or fusion.

21. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
LOW GRADE ENERGY
AVAILABILITY
AVAILABLE ENERGY (EXERGY):
It is that portion of the amount of heat energy supplied to a reversible
engine which could be converted into useful work.
UNAVAILABLE ENERGY (ANERGY): :
It is that portion energy which cannot be converted into useful work by
any means.

22. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
AVAILABLE ENERGY

23. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
AVAILABLE ENERGY AND UNAVAILABLE ENERGY

24. AE 2031 APPLIED THERMODYNAMICS S. Y. B. Tech.
Thank You !