# Third law of thermodynamics and mixtures

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).

Mapes
Homework Helper
Gold Member
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