[YAPA] entropy

[Michael Crescimanno]

Hi YAPA!! I miss you all (been away all year)!! Hey, Norma, excellent 
question. I believe that what that entropy refers to assumes the 
Nernst postulate; that the entropy of a material at zero temperature 
(absolute) is zero. 

Nernst had a student measuring entropy changes in 
various gasses and gas mixtures when during -as I understand it- 
the student's doctoral defense Nernst realized that all these 
entropy changes were only consistent with one another if the 
entropy at absolute zero was zero for each component. Viola! 

Ergo, Nernst's postulate. Really comes from experiment that predated 
the Boltzmann view of entropy, though it is (generally) consistent with it.  

For any gas, as  you give it heat dQ the temperature rises. Sum
up all the dQ/T from absolute zero and I think that you get that
quoted #. Thus note one non-trivial thing about Nernst's postualate is 
that the specific heat at low temps must go to zero. 

Peace, have fun at the Zitto BBQ; I can't wait to get back to Ytown and 
merrilly struggle with this all with you all again !! -mike 


====================================================================
Michael Crescimanno                              mcrescim at cc.ysu.edu
Assoc. Professor of Physics                      Tel: (330)-941-7109
Department of Physics and Astronomy
Youngstown State University                      Fax: (330)-941-3121
Youngstown, OH 44555-2001	     http://www.as.ysu.edu/~mcrescim
====================================================================

On Fri, 23 May 2008, norma.holowach wrote:

> Teachers,
> A student asked me a question in which I have not been able to find an answer. 
> How is the entropy level of a substance determined? How is the zero value 
> defined?  For example, a reference I have gives the entropy(S) of oxygen gas 
> at 25 degrees Celsius and 100.00 kPa a value of 205.138 J/(mol*K). How was 
> that value determined?
> 
> Thank you.
> 
> Norma Holowach, M.Ed
> National Board Certified Teacher
> Praxis III Assessor
> Lakeview High School
> 300 Hillman Drive
> Cortland, OH  44410
> (330)637-4921
> "Connecting with nature is an essential part of being alive."
> National Geographic.
> 
> 
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