1. The problem statement, all variables and given/known data This isn't an actual problem, it's just a question based on my reading. Reif says "If the external parameters of a thermally isolated system are changed quasi-statically by any amount, ΔS = 0." I don't understand why it has to be thermally isolated. Looking at the entropy relation [tex] dS = dq/T [/tex] There isn't any work in there, and the derivation didn't set work = 0. So if a system undergoes a reversible process and dQ is non-zero, it seems that work also has no effect on the entropy change?