How Are the Two Formulations of the Third Law of Thermodynamics Equivalent?

AI Thread Summary
The discussion centers on the two formulations of the Third Law of Thermodynamics: the impossibility of cooling a body to absolute zero through any finite process and the cessation of all processes as a system approaches absolute zero, leading to minimum entropy. Participants debate the equivalence of these formulations, with some arguing that reaching absolute zero negates the concept of minimum entropy. The conversation references a thermodynamics lecturer's summary of the laws, emphasizing the futility of trying to reach absolute zero. There is also mention of a specific text by Landsberg that suggests the formulations are not equivalent. Overall, the thread explores the nuances of thermodynamic principles and their interpretations.
paweld
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The are at least two different formulation of third law of thermodynamics:
(1) it's impossible to cool a body to absolute zero by any finite process,
(2) as a system approaches absolute zero, all processes cease and the entropy
of the system approaches a minimum value.
I don't know why they are equivalnet. Can anyone explain it to me?
Thanks.
 
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Generically, cooling something means making it stand still. You're taking the kinetic energy away from it (your table, chair, and even the snow at -40 F in my backyard in the winter all have rapidly moving molecules in them and lots of energy compared to something near 0 K).

Another way to put it, you're ordering the system... reducing it's entropy. If the system reaches a state where it's at its minimum entropy... i.e. minimum disorder... i.e. maximum order, than you can't get it to "sit still" anymore than that. It's as ordered as it's going to get.
 
My old thermodynamics lecturer summed up the three laws of thermodynamics thus
You can't win
You can't even break even
You can't even leave the game
 
They are not equivalent, see Landsberg, "Thermodynamics and statistical mechanics", Dover Publ.
 
DrDu said:
They are not equivalent, see Landsberg, "Thermodynamics and statistical mechanics", Dover Publ.

which chapter?
 
Jobrag said:
My old thermodynamics lecturer summed up the three laws of thermodynamics thus
You can't win
You can't even break even
You can't even leave the game

I like it :smile:

paweld said:
The are at least two different formulation of third law of thermodynamics:
(1) it's impossible to cool a body to absolute zero by any finite process,
(2) as a system approaches absolute zero, all processes cease and the entropy
of the system approaches a minimum value.
I don't know why they are equivalnet. Can anyone explain it to me?
Thanks.
Notice the "minimum value" in (2). That's the same as "impossible to cool a body to absolute zero" in (1). If you could get something to absolute zero, then there is no "minimum value".
 
Jobrag, were you at Sussex? My lecturer there used those exact phrases. His name was John Barrow.

Mat
 
I had a lecturer who said that to. I think it's fairly common.
 

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