[Twickel]

Hi
This is in reference to slide 7-8 of the attached file. I understand that it is not convenient to write things in terms of Entropy of system + Entropy of surroundings all the time, so instead we need to derive the Free energy formulas.

I do not understand how we get there.
If  dS = dSsys+dSbath = 0 and heat flows into the system from the bath. Is the entropy of the system at constant N and V now ds=qin/T? Why does the surroundings part of the =0 equation become -dUsys/T and the dSsystem part of the equation stay as dSsys
yielding, dSsys - dUsys/T = 0

Thank you

Here is the powerpoint that has a diagram and the equation with explanation ( which I do not get) on slide 7 :https://rapidshare.com/files/2007495848/lecture_9_2012_GGW (1).ppt