1. The problem statement, all variables and given/known data Consider all possible isothermal contractions of an ideal gas. The change in entropy of the gas: A) does not increase for any of them B) increases for all of them C) is zero for all of them D) decreases for all of them E) does not decrease for any of them 2. Relevant equations [tex]\Delta S\geq 0[/tex] [tex]\Delta S = Sf -Si[/tex] [tex]\Delta S = Q/T [/tex] (isothermal process) 3. The attempt at a solution I chose answer E since my physics book states that "in a closed system, the entropy of the system increases for irreversible processes and remains constant for reversible processes. It never decreases." However, the answer key has the correct answer as D. I think it might have something to do with the isothermal modifier, but I'm not exactly sure of the logic.