Change in Entropy in Surroundings [ENDORSED]

[Mary Becerra 2D]

Why is it that when involved in an isothermal reversible expansion, the change in S of surroundings is equal to the opposite sign of the change in S of the system but when involved in an isothermal nonreversible free expansion, the change in S of surroundings is equal to zero?

[Chem_Mod]

In a free expansion no work is done: w = 0
Isothermal: Delta U = 0

Therefore, q = 0

Since no heat exchanged with the surroundings there is no entropy change in the surroundings.

Ask me this question in my Monday review as other students probably have the same question.

[Yeyang Zu 2J]

First, you can think of that everything is constant in the universe
Then, since Stotal=q(total)/T
Qtotal=zero
Stotal=0