## Positional/Residual Entropy

Boltzmann Equation for Entropy: $S = k_{B} \ln W$

Alison Trinh 1E
Posts: 104
Joined: Thu Jul 25, 2019 12:16 am

### Positional/Residual Entropy

What makes positional/residual entropy different from entropy in general?

Eugene Chung 3F
Posts: 142
Joined: Wed Nov 15, 2017 3:03 am

### Re: Positional/Residual Entropy

residual entropy is the left-over entropy at 0K. (perfect crystal). The entropy in this case would only depend on the ways in which molecule can position/orient themselves.

Venus_Hagan 2L
Posts: 104
Joined: Fri Aug 02, 2019 12:16 am

### Re: Positional/Residual Entropy

If a molecule consists of all the same atoms or the atoms can be in multiple places within the molecule (resonance) then it has no positional entropy and at 0 Kelvins, the molecule would have no entropy. Ex BF3. If the molecule has different molecules like COF2, then the oxygen can be in multiple places and thus has positional entropy. At 0 Kelvin, it would still have some entropy.

rohun2H
Posts: 100
Joined: Wed Sep 18, 2019 12:19 am

### Re: Positional/Residual Entropy

A molecule at 0 K will have 0 residual entropy, but only if it is perfectly ordered will the molecule have 0 entropy, if it is not perfectly ordered then some entropy will still be present.

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