This document discusses entropy in engineering thermodynamics. It defines entropy as a function that shows the possibility of converting heat into work. Entropy increases at a lower rate when heat is added at high temperatures compared to low temperatures. Maximum entropy corresponds to minimum availability to convert heat into work, and minimum entropy corresponds to maximum availability. Entropy can be considered a measure of microscopic disorder in a system. Irreversible processes are associated with a transition from ordered to more disordered states of energy. Mixing gases increases entropy by creating a more random arrangement. Characteristics of entropy include: it is a property of the system, changes depend on temperature for reversible processes, and it is an extensive property expressed in units of energy per degree of temperature.

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• Now partition be withdrawn, allowing the two gases to mix.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.

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.