Thermodynamics
Thermodynamics Lecture notes
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Second Law of Thermodynamics
Introduction
First law is a statement of conservation of energy principle. Satisfaction of first law alone does not ensure
that the process will actually take place.
A cup of hot coffee left in a cooler room eventually cools off.
This process satisfies the first law.
The reverse of this process – coffee getting hotter as a result of
heat transfer from a cooler room does not take place.
Consider the heating of a room by the passage of electric current
through a resistor.
This process satisfies the first law.
The reverse of this process – transferring some heat to the wires
does not cause an equivalent amount of electric energy to be
generated in the wires.
• Processes proceed in a certain direction and not in the reverse direction
• The first law places no restriction on the direction of a process, but satisfying the first law does not
ensure that the process can actually occur.
• This inadequacy of the first law to identify whether a process can take place is remedied by introducing
another general principle, the second law of thermodynamics.
• The reverse processes discussed above violate the second law of thermodynamics. This violation is
easily detected with the help of a property, called entropy.
• A process will not occur unless it satisfies both the first and the second laws of thermodynamics
• The use of the second law of thermodynamics is not limited to identifying the direction of processes.
• The second law also asserts that energy has quality as well as quantity. However, the first law is
concerned with the quantity of energy and the transformations of energy from one form to another
with no regard to its quality.
• The second law of thermodynamics is also used in determining the theoretical limits for the
performance of engineering systems, such as heat engines and refrigerators, as well as predicting
the degree of completion of chemical reactions.
Download - Click Here Second Law of Thermodynamics
Introduction
First law is a statement of conservation of energy principle. Satisfaction of first law alone does not ensure
that the process will actually take place.
A cup of hot coffee left in a cooler room eventually cools off.
This process satisfies the first law.
The reverse of this process – coffee getting hotter as a result of
heat transfer from a cooler room does not take place.
Consider the heating of a room by the passage of electric current
through a resistor.
This process satisfies the first law.
The reverse of this process – transferring some heat to the wires
does not cause an equivalent amount of electric energy to be
generated in the wires.
• Processes proceed in a certain direction and not in the reverse direction
• The first law places no restriction on the direction of a process, but satisfying the first law does not
ensure that the process can actually occur.
• This inadequacy of the first law to identify whether a process can take place is remedied by introducing
another general principle, the second law of thermodynamics.
• The reverse processes discussed above violate the second law of thermodynamics. This violation is
easily detected with the help of a property, called entropy.
• A process will not occur unless it satisfies both the first and the second laws of thermodynamics
• The use of the second law of thermodynamics is not limited to identifying the direction of processes.
• The second law also asserts that energy has quality as well as quantity. However, the first law is
concerned with the quantity of energy and the transformations of energy from one form to another
with no regard to its quality.
• The second law of thermodynamics is also used in determining the theoretical limits for the
performance of engineering systems, such as heat engines and refrigerators, as well as predicting
the degree of completion of chemical reactions.
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