Second Law of Thermodynamics Notes | EduRev

: Second Law of Thermodynamics Notes | EduRev

 Page 1


Chapter 6
Second Law of Thermodynamics
Page 2


Chapter 6
Second Law of Thermodynamics
It is now clear that we can’t construct a heat engine with just one 
+ve heat interaction.
Leads Up To Second Law Of 
Thermodynamics
The above engine is not possible.
Page 3


Chapter 6
Second Law of Thermodynamics
It is now clear that we can’t construct a heat engine with just one 
+ve heat interaction.
Leads Up To Second Law Of 
Thermodynamics
The above engine is not possible.
Second Law Of Thermodynamics
(contd…)
Is it possible to construct a heat engine with only one -ve 
heat interaction? 
Is the following engine possible?
The answer is yes, because 
This is what happens in a 
stirrer
Page 4


Chapter 6
Second Law of Thermodynamics
It is now clear that we can’t construct a heat engine with just one 
+ve heat interaction.
Leads Up To Second Law Of 
Thermodynamics
The above engine is not possible.
Second Law Of Thermodynamics
(contd…)
Is it possible to construct a heat engine with only one -ve 
heat interaction? 
Is the following engine possible?
The answer is yes, because 
This is what happens in a 
stirrer
Second Law Of Thermodynamics
(contd…)
Perpetual motion machine of the second kind is not possible.
Perpetual motion machine of 
the first kind violates I LAW 
(It produces work without 
receiving heat)
W
Page 5


Chapter 6
Second Law of Thermodynamics
It is now clear that we can’t construct a heat engine with just one 
+ve heat interaction.
Leads Up To Second Law Of 
Thermodynamics
The above engine is not possible.
Second Law Of Thermodynamics
(contd…)
Is it possible to construct a heat engine with only one -ve 
heat interaction? 
Is the following engine possible?
The answer is yes, because 
This is what happens in a 
stirrer
Second Law Of Thermodynamics
(contd…)
Perpetual motion machine of the second kind is not possible.
Perpetual motion machine of 
the first kind violates I LAW 
(It produces work without 
receiving heat)
W
Statement 1: It is impossible to construct a device which 
operating in a cycle operating in a cycle will produce no effect other than raising of 
a weight and and exchange of heat with a single single reservoir.
Note the two underlined words.
II Law applies only for a cycle - not for a process!! (We already 
know that during an isothermal process the system can exchange 
heat with a single reservoir and yet deliver work)
!!There is nothing like a 100% efficient heat engine!!
Enunciation of II Law of Thermodynamics
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