## 2nd law -- conceptual

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

Lucia H 2L
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### 2nd law -- conceptual

I know that the 2nd law of thermodynamics states that in an isolated system, entropy is always increasing.

How does this change in a non-isolated system? In normal problems, is it legal for deltaS surroundings or deltaS total to have negative values?

Nina Gautam 1K
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Joined: Fri Sep 29, 2017 7:04 am

### Re: 2nd law -- conceptual

I believe that in a non-isolated system, delta S can be negative because work can be done on the system to decrease the entropy.

Masih Tazhibi 2I
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### Re: 2nd law -- conceptual

The idea behind this law is that the universe is always heading towards some increase in entropy. The entropy of the surroundings plus the entropy of the system is greater than zero because in a spontaneous process, the system has not reached thermal equilibrium. Since Entropy is Q/T, having the same but opposite heat flow to the system and surroundings, but different temperatures, leads to the change in entropy values not canceling out. In this way, you will see that the addition of the entropy of the system and the surroundings, more specifically the entropy of the universe, will be greater than zero until the model reaches thermal equilibrium, in which case it becomes zero.

Glendy Gonzalez 1A
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Joined: Fri Sep 29, 2017 7:07 am

### Re: 2nd law -- conceptual

Technically, you can have a negative entropy. It would just mean it is not favorable and would not occur frequently.