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Subject: Engineering Thermodynamics
Topic: Entropy
Name: Nilrajsinh Vasandia
Branch: Mechanical
En No.:- 130990119060
Entropy
• Entropy is a function of quantity of heat which shows the
possibility of conversion of that heat into work.
• The increase in the entropy is lower when heat is added at a
high temperature and the increase in entropy is higher when
heat is added at a low temperature
• The maximum entropy means , there is minimum availability
for conversion into work and the minimum entropy means ,
there is maximum availability for conversion into work.
• Consider the heating of working substance by reversible
process.
• Let heat supplied to
the working substance
in process which will
increase the entropy by
dS.
• Heat supplied to
reversible process
Q
TdsQ 
Where, T = absolute temperature, dS = Increse in entropy
Total heat supplied or absorbed
Also, change in entropy
dsTQ  
2
1
2
1

T
Q
ds


 
2
1
2
1
T
Q
ds


2
1
12
T
Q
SS

Entropy & Disorder
• Entropy can be considered to be a measure of microscopic
disorder.
• Work interaction can be considered ordered molecular
energy. While heat interaction can be considered disordered
molecular energy.
• All irreversible processes are associated with a transition
from ordered molecular energy to disordered molecular
energy.
• Let us consider a box with a partition dividing it into two
sections contains only O2 molecules in one section and only
N2 molecules in the other section.
• Now partition be withdrawn, allowing the two gases to mix.
This process is irreversible ( since system can not be returned
to its original state without taking work from surroundings
).This process is accompanied by an increase in entropy.
• The mixing process has resulted in a more random
arrangement of the system, hence an increase in entropy can
be associated with a change from a more ordered to less
ordered, or more random state. The more a system
approaches equilibrium, the greater is the disorder and
irreversibility and when equilibrium is reached, it has the
maximum disorder.
• In other word, “entropy is a measure of the disorder of the
system.”
• A measure of molecular disorder can be found in a molecular
mean free path. Thus, whenever there is an increase in the
volume in the microscopic motion of the individual particles
of matter, the entropy increases.
Characteristics of entropy
• Entropy is property of system.
• For reversible process change in entropy is
• Entropy is point function, independent on path
of the process.
for reversible process
for irreversible process
T
Q
SS
rev


2
1
12
0  gsurroundinsystem SS
0  gsurroundinsystem SS
• Entropy is extensive property.
• It is expressed as energy units per unit degree temperature
KJ/K.

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Entropy

  • 1. Subject: Engineering Thermodynamics Topic: Entropy Name: Nilrajsinh Vasandia Branch: Mechanical En No.:- 130990119060
  • 2. Entropy • Entropy is a function of quantity of heat which shows the possibility of conversion of that heat into work. • The increase in the entropy is lower when heat is added at a high temperature and the increase in entropy is higher when heat is added at a low temperature • The maximum entropy means , there is minimum availability for conversion into work and the minimum entropy means , there is maximum availability for conversion into work.
  • 3. • Consider the heating of working substance by reversible process. • Let heat supplied to the working substance in process which will increase the entropy by dS. • Heat supplied to reversible process Q TdsQ  Where, T = absolute temperature, dS = Increse in entropy
  • 4. Total heat supplied or absorbed Also, change in entropy dsTQ   2 1 2 1  T Q ds     2 1 2 1 T Q ds   2 1 12 T Q SS 
  • 5. Entropy & Disorder • Entropy can be considered to be a measure of microscopic disorder. • Work interaction can be considered ordered molecular energy. While heat interaction can be considered disordered molecular energy. • All irreversible processes are associated with a transition from ordered molecular energy to disordered molecular energy.
  • 6. • Let us consider a box with a partition dividing it into two sections contains only O2 molecules in one section and only N2 molecules in the other section. • Now partition be withdrawn, allowing the two gases to mix. This process is irreversible ( since system can not be returned to its original state without taking work from surroundings ).This process is accompanied by an increase in entropy.
  • 7. • The mixing process has resulted in a more random arrangement of the system, hence an increase in entropy can be associated with a change from a more ordered to less ordered, or more random state. The more a system approaches equilibrium, the greater is the disorder and irreversibility and when equilibrium is reached, it has the maximum disorder. • In other word, “entropy is a measure of the disorder of the system.” • A measure of molecular disorder can be found in a molecular mean free path. Thus, whenever there is an increase in the volume in the microscopic motion of the individual particles of matter, the entropy increases.
  • 8.
  • 9. Characteristics of entropy • Entropy is property of system. • For reversible process change in entropy is • Entropy is point function, independent on path of the process. for reversible process for irreversible process T Q SS rev   2 1 12 0  gsurroundinsystem SS 0  gsurroundinsystem SS
  • 10. • Entropy is extensive property. • It is expressed as energy units per unit degree temperature KJ/K.