Entropy change for reversible processes


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Glenda Marshall DIS 3M
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Joined: Sat Sep 27, 2014 3:00 am

Entropy change for reversible processes

Postby Glenda Marshall DIS 3M » Fri Jan 23, 2015 4:29 pm

Why is total change in entropy zero for a reversibly expanding gas?

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Re: Entropy change for reversible processes

Postby Chem_Mod » Mon Jan 26, 2015 4:30 pm

See Example 8.12a for the mathematical explanation.

Conceptually, you can think of entropy as some property that governs the direction of change. If the total entropy of the universe increases with the transformation A-->B, then it proceeds forward. If negative, it proceeds backwards instead. A reversible process is neither proceeding forward nor backward at any time, since it is in equilibrium at every moment. So, the entropy is neither positive nor negative, meaning it is zero.

Justin Le 2I
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Re: Entropy change for reversible processes

Postby Justin Le 2I » Tue Jan 27, 2015 11:45 pm

I think the pictures on page 312 are also really helpful in understanding why the total change in S is zero for a reversible system and why deltaSsurr for irreversible systems is zero.

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