## s vs. delta s

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

Sophie Krylova 2J
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Joined: Fri Sep 29, 2017 7:06 am

### s vs. delta s

In what context do we talk about Entropy vs change in entropy?

Minie 1G
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### Re: s vs. delta s

most of the times in calculations it's delta s, because we are measuring the entropy of some reaction and therefore take the entropy of the products minus reaction (thus a change in entropy).

Johann Park 2B
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### Re: s vs. delta s

When dealing with statistical/residual entropy and the make-up of molecules and crystals, we will use S = K + ln W to calculate is as a value. When dealing with reactions and changes, we have delta S = q/T and other derivations that reflect delta S as a state function.

David Minasyan 1C
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Joined: Thu Jul 13, 2017 3:00 am

### Re: s vs. delta s

Just to add on, the S in the residual entropy is like the minimum energy of the molecule - it's the entropy that the molecule has without anything being done to it. That's about the only time we use S instead of delta S.

Sirajbir Sodhi 2K
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### Re: s vs. delta s

S is the entropy of a substance while delta S is the change in entropy. We use S to calculate delta S of a reaction (entropy of products - entropy of reactants). Delta S is generally more useful than S as we can calculate changes in entropy for various processes.

andrewr2H
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### Re: s vs. delta s

S is generally used in reference to to the statistical/residual entropy of a perfectly ordered crystal at 0 K. It’s equation is s = kb * lnW

Justin Folk 3I
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### Re: s vs. delta s

I thought we can only measure change in entropy?

Ashley Macabasco 2K
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### Re: s vs. delta s

Justin Folk 3I wrote:I thought we can only measure change in entropy?

Positional entropy does not measure the change in entropy, but the entropy possible through the number of particles and the position of such particles in the formula S = klnW.