Total Entropy Change

$\Delta S = \frac{q_{rev}}{T}$

Lisa Tang 1C
Posts: 62
Joined: Fri Sep 29, 2017 7:05 am
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Total Entropy Change

The equation for total entropy change is $\Delta$Stotal=$\Delta$Ssystem + $\Delta$Ssurr. My question is why doesn't the entropy change of the system always equal the entropy change of the surroundings? I know that only when the total entropy change is positive will the process be spontaneous, but how are the two entropies not equal to each other with their signs switched?

Curtis Tam 1J
Posts: 105
Joined: Thu Jul 13, 2017 3:00 am

Re: Total Entropy Change

I think if you were to have a free expansion for example, the entropy of the system increases because the volume increases, leading to more possible microstates. However, work is not done on the surroundings because the system is not pushing against any constant pressure. Therefore, the surroundings do not change in entropy.