2nd Law of Thermodynamics

Pause and ponder

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

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.

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

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

Intuitive understanding of entropy

•Entropy can be thought as a register or counter of the number ofways a system can store internal energy

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.

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

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.

What is entropy?1.) Entropy is directly connected to the number of macrostates a

system can have for a given microstate and2.) 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.

Pause and ponder

Is it possible for entropy to decrease? Why or why not?

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.

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.

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.

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

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.

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.

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.

Group and Class Project1.) 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'

References1.) 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.htm6.) Website: Google Images