Third law of thermodynamics and mixtures

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Discussion Overview

The discussion revolves around the implications of the third law of thermodynamics, particularly in relation to the entropy of mixtures of ideal quantum gases at absolute zero temperature. Participants explore whether the entropy of mixing is zero under these conditions and the assumptions involved in the formulation of the law.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant asserts that the entropy of a mixture of two different ideal quantum gases at 0K is zero, suggesting that both pure gases would also have zero entropy.
  • Another participant questions this assertion, pointing out that there are many ways to arrange the mixture of particles A and B, which could imply a non-zero entropy of mixing.
  • A third participant speculates that the third law may only apply to one-component systems and expresses uncertainty about whether this assumption is typically made in the law's formulation.
  • Another participant notes that the third law was originally intended to apply to perfect crystals and raises concerns about isotopic variations in pure substances, suggesting that the statement regarding the entropy of a perfect crystal at absolute zero is not absolute and depends on certain assumptions.

Areas of Agreement / Disagreement

Participants express differing views on whether the entropy of mixing is zero at absolute zero, and there is no consensus on the assumptions underlying the third law of thermodynamics as it pertains to mixtures.

Contextual Notes

The discussion highlights potential limitations in the assumptions made about the third law, particularly regarding multi-component systems and the nature of perfect crystals. There are unresolved questions about the implications of isotopic variations and the mathematical formulation of entropy.

paweld
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Is it true that entropy of mixture of twodifferent ideal quantum gases
at 0K temperature is equal 0 that is the entropy of mixing is 0 at 0K
(two pure gases would have also 0 entropy).
 
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Why would the entropy of mixing be zero when there are many ways to arrange the mixture of particles A and B?
 
I suppose then that the third law works only for one component system.
But I don't know if these assumption is made usually in formulation of this law.
If not entropy of mixing should be 0. But I have no idea why?
 
The third law is (was) meant to apply only to perfect crystals.

Even this has its issues because even pure substances have isotopic variation in composition.

Even the statement "The entropy of a perfect crystal at absolute zero is zero" is not absolute. It relies on setting to zero the constant of integration inherent in

S = kln(Z) + U/T + Constant
 

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