## Entropy change for reversible processes

Volume: $\Delta S = nR\ln \frac{V_{2}}{V_{1}}$
Temperature: $\Delta S = nC\ln \frac{T_{2}}{T_{1}}$

Glenda Marshall DIS 3M
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### Entropy change for reversible processes

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

Chem_Mod
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### Re: Entropy change for reversible processes

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

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.