The 2nd Law of Thermodynamics states that entropy, a measure of the number of microscopic arrangements of a system, always increases over time. Entropy is often misunderstood but can be calculated and measured. It is directly related to the number of possible macrostates a system can have for a given microstate and represents the system's degrees of freedom. While reversibility is theoretically possible, natural processes are irreversible and always lead to an increase in entropy. Rudolf Clausius originated the concept of entropy and demonstrated that heat transfer between objects always results in an overall rise in entropy across systems.

1. 2nd Law of Thermodynamics

2. Pause and ponder
Imagine you are watching your favorite movie. How could you
tell it was being played in reverse?

3. Why entropy?
Entropy is a non-intuitive but absolutely essential parameter of the
2nd law of thermodynamics, along with the more common parameters
of volume, pressure, temperature and number of molecules.

4. There is a lot of misrepresentation
of entropy
•Concept of entropy gets misrepresented or misunderstood many
times, including scientists.
• Entropy sometimes is said to measure disorder,
randomness, smoothness, dispersion, homogeneity

5. Scientists
Josiah Gibbs John von Neumann
•Gibbs called entropy “ mixed upedness”
•Von Neumann said “ nobody knows what entropy is anyways”
• Contemporary scientists have a firm grasp of the meaning of
entropy
•Entropy can be measured and calculated

6. Intuitive understanding of entropy
•Entropy can be thought as a register or counter of the number of
ways a system can store internal energy

7. Example: What does temperature tell us?
•Water molecules have a certain number of degrees of freedom. Each
molecule can rotate, translate, vibrate and bond to other molecules.
•Imagine a glass of water. What does the temperature of the water
tell us? The temperature is the overall effect of the degrees of
freedom of the water molecules.

8. What is the microstate of a system?
A microstate is the complete description of all the microscopic
arrangements of a system.

9. What is the macrostate of a system?
A macrostate is a description of the conditions of the system from a
macroscopic point of view and makes use of macroscopic variables
such temperature, temperature and pressure.

10. What is entropy?
1.) Entropy is directly connected to the number of macrostates a
system can have for a given microstate and
2.) Is a measure of the number of degrees of freedom the system
posseses.
Warning: Do not confuse entropy with a system exhibiting
randomness or disordered.

11. Pause and ponder
Is it possible for entropy to decrease? Why or why not?

12. Class activity
Fill in two grids with 100 squares each such that one grid displays
greater entropy than the other grid. Explain the rules you used for
filling the squares.

13. What is a reversible process?
In a reversible process, the system undergoing the process can be
returned to its initial conditions along the same path shown in a
pV-diagram and every point along this path is an equilibrium state.
Note that reversibility is an extremely useful theoretical concept.

14. Definition of entropy
If a process is completely reversible then entropy can be defined
during a thermodynamic process as the change in heat flow over
the temperature. The standard units of entropy are joules(J) per
Kelvin (K). Important to remember that heat is path dependant.
The 2nd law of thermodynamics affirms that entropy is a state
function but heat is not a state function because it’s path
dependant.

15. Pause and ponder
Are there any naturally reversible processes occurring in nature? If
not, why is the concept of reversibility useful?

16. Rudolf Clausius (1822-1888)
Concept of entropy originated with Rudolf Clausius. He was
investigating the phenomena of why heat always flows from a high
temperature body to a low temperature body and why never the
reverse occurs naturally in nature.

17. Natural heat flow
•Rufolf Clausius was able to demonstrate when heat flows from the
high temperature object to the low temperature object the entropy
change of the low temperature object during the heat transfer is
larger than the entropy change of the hot object.
•Clausius then found that any heat transfer results in a total
increase of the sum of the entropy of the two objects.

18. 2nd Law of Thermodynamics
Clausius discovered that all real natural processes which occur in
nature always increase the entropy of the universe and that is the
2nd law of thermodynamics. The law now can explain why heat
always flows from a high temperature system to a low temperature
system.

19. Group and Class Project
1.) Applying the laws of thermodynamics, how is human activity
causing climate change?
2.) What alternative sources of energy is available to reduce the
impact of burning fossil fuels.
To view videos about climate change go to the links below.
Climate Change Impact: NASA's 21st Century Predictions
What is climate Change?
Teachers TV- Climate Change - The Causes
NASA | Feeling the Sting of Climate Change
Noam Chomsky: How Climate Change Became a 'Liberal Hoax'

20. References
1.) Ben-Naim, A. (2012). Entropy and the Second Law (1st ed.).
2.) Lerner, L. (1996). Physics for Scientists and Engineers (1st ed).
3.) Serway, R. (2000). Physics for Scientists and Engineers (5th ed).
4.) Wark, K. (1977). Thermodynamics (3rd ed.).
5.) WebSite: MIT OpenCourseWare, http://ocw.mit.edu/index.htm
6.) Website: Google Images