## 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.

**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(U_{f}^{3/2}/U_{i}^{3/2})
= (3/2) N k ln 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.

**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.

**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.

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

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