1. Lon-Capa 4th HW assignment due tonight by 5 pm.
3rd Quiz due Sunday, 10/9 by 10 pm. It will open today at 5 pm.
5th HW assignment is also open!
Videos for Section 9.3.

2. Laws of Thermodynamics
First Law
The quantity of energy is conserved.
Energy of the universe is constant.
“You cannot win, you can only break even.”
Second Law
The quality of energy is not conserved. It’s usefulness decreases.
Entropy of the universe tends toward a maximum.
“You cannot break even.”

3. We will… …show how probability plays into all of this.
…show that thermal equilibrium is preferred when two bodies of different temperatures are put in contact with one another.
…see why entropy is related to the logarithm of the number of configurations or microstates.
…discuss what “reversible” means when we say the change is entropy equals qrev/T?

4. A Two-molecule System

5. Big Ideas
The probability of occurrence for a particular arrangement depends on the number of microstates in which that arrangement can be achieved.
Nature is governed by probability.

6. A four-molecule system.
The most likely state is two molecules in both bulbs.

7. Calculation of interest
We are interested in how the most probable arrangement dominates as we increase the number of molecules in our sample. That is:

8. The Four-molecule System

9. Microstate fraction vs. mole fraction

10. One mole of gas

11. “Pressure Equilibrium”
“Pressure equilibrium” is the most probable way of sharing a fixed number of particles in a fixed container.

12. Thermal Equilibrium
Hot  Cold so that temperatures are the same
Thermal equilibrium is the most probable way of sharing a fixed amount of energy among a fixed number of atoms.