Chapter 18, Problem 64PCE

Predict/Explain (a) A gas is expanded reversibly and adiabatically. Does its entropy increase, decrease, or stay the same? (b) Choose the best explanation from among the following:

1. I.            The process is reversible, and no heat is added to the gas. Therefore, the entropy of the gas remains the same.
2. II.            Expanding the gas gives it more volume to occupy, and this increases its entropy.
3. III.            The gas is expanded with no heat added to it, and hence its temperature will decrease. This, in turn, will lower its entropy.