s vs. delta s


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Sophie Krylova 2J
Posts: 59
Joined: Fri Sep 29, 2017 7:06 am

s vs. delta s

Postby Sophie Krylova 2J » Thu Feb 15, 2018 1:17 pm

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

Minie 1G
Posts: 63
Joined: Fri Sep 29, 2017 7:04 am

Re: s vs. delta s

Postby Minie 1G » Thu Feb 15, 2018 3:01 pm

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

Postby Johann Park 2B » Thu Feb 15, 2018 4:52 pm

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

Postby David Minasyan 1C » Fri Feb 16, 2018 12:18 am

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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Joined: Sat Jul 22, 2017 3:00 am

Re: s vs. delta s

Postby Sirajbir Sodhi 2K » Fri Feb 16, 2018 4:25 pm

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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Joined: Fri Sep 29, 2017 7:05 am

Re: s vs. delta s

Postby andrewr2H » Fri Feb 16, 2018 4:48 pm

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

Postby Justin Folk 3I » Fri Feb 16, 2018 5:17 pm

I thought we can only measure change in entropy?

Ashley Macabasco 2K
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Joined: Fri Sep 29, 2017 7:05 am

Re: s vs. delta s

Postby Ashley Macabasco 2K » Sat Feb 17, 2018 2:20 pm

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.


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