## PHYS 317 Reading Assignment #8

Read section 2.6 and answer the following questions by email, hardcopy, or web form before class Friday, September 19.

1. According to equation (2.51), doubling the volume of a monatomic ideal gas with fixed U, N gives an entropy change Delta S = N k ln(2). What is the analogous expression for Delta S if instead the energy is doubled at constant V, N?

Delta S = N k ln(Uf3/2/Ui3/2) = (3/2) N k ln 2

2. Is the work done in free expansion positive, negative, or zero?

Zero. There is no moving wall that the particles in the gas can push on. They push on the static wall -> no work done.

3. A chamber is divided in half by a partition, and both halves are filled with an equal number of A molecules. Does the entropy increase significantly if the partition is then removed? What if initially A molecules are on the left and an equal number of B molecules are on the right?

If an equal number of A particles on both sides: No it doesn't increase noticebly. If there are an equal number of A and B particles on either side, then you can see the increased entropy that's due to the entropy of mixing.

4. Can heat flow reversibly from a hotter object to a cooler object that is 10 K cooler?

No, heat flow between objects of differing tempertatures is irreversible. Always.

5. Was there anything you had particular difficulty with in this reading? Is so, describe briefly.