absolute zero and entropy

[thebillsfan]

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absolute zero is defined as minimum entropy. is it NOT possible to have absolute zero entropy, since entropy can only be measured in relative terms?

 

[kentavr]

absolute zero is defined as minimum entropy. is it NOT possible to have absolute zero entropy, since entropy can only be measured in relative terms?

Entropy can be calculated (measured) in absolute terms and it is. The way how it is done will be outside MCAT curriculum, but if you want to know, according to statistical physics the measure of disorder of substance is the average of probability of all micro states of the body. More precise S=-k*Sum(p*Ln(P)) Where P is probability of particular micro state. At absolute zero there is only one possible state (no movements) which gives Ln(1)=0 in the formula and therefore S=0 at 0K. However, This state contradicts Quantum mechanics postulates and question become even more complicated.

You will not make a huge mistake if you will think that at T=0K S=0. But keep in mind that T=0K is not achievable according to the third law of thermodynamics.

 

[RogueUnicorn]

there's a concept called residual entropy, the entropy of matter at absolute zero, and covered in advanced p-chem classes. like the poster above points out, (and i think i've made this point once before to you) entropy can be calculated, unlike enthalpy

 

[wanderer]

there's a concept called residual entropy, the entropy of matter at absolute zero, and covered in advanced p-chem classes. like the poster above points out, (and i think i've made this point once before to you) entropy can be calculated, unlike enthalpy

That's pretty interesting (and seemingly contradictory to what I learned in gen chem). Thanks!