Frequently asked questions:
Q: On the first section (1) of the first exam, I noticed that I got one point off
for every mistake I made, except for one question where I got three points
off for one mistake. How was this section graded?
A: The questions in that section were each worth 3 points (one sentence had two selections in it, each worth 3 points). Partial credit was given, however, so that not all errors resulted in the loss of the full 3 points.
Q: I have a quick question about problem 9(a) in chapter 2. I see
that you used q = Pex(V2-V1) to calculate q. I am wondering how you know
to use this (for an irreversible process) as opposed to qT = nRT*ln(P1/P2)
(for a reversible process). In other words, how do you know that the
process is irreversible?
A: The key element in this question is "against a constant external pressure." In a reversible process, the pressure is always following the volume (in equilibrium at all times), so it is not constant.
Q: In Problem 8b., you say the change in E = nCv(T2-T1)
I thought this was applicable only when the volume was constant. Can this
formula be used for any change in P,V,orT of an ideal gas?
A: Yes. Note that n, E and T are state variables, so it doesn't matter whether you get to the same final state reversibly or irreversibly.