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

In summary, the third law of thermodynamics has at least two different formulations: (1) it's impossible to cool a body to absolute zero by any finite process, and (2) as a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value. These formulations may seem equivalent, but they are not. In (1), cooling a body to absolute zero means reducing its entropy to the minimum possible value. In (2), the system already has reached its minimum entropy at absolute zero, so there is no further cooling possible. This is summarized by the saying, "You can't win, you can't even break even, you can't even leave the game." The third law of thermodynamics is
  • #1
paweld
255
0
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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  • #2
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.
 
  • #3
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
 
  • #4
They are not equivalent, see Landsberg, "Thermodynamics and statistical mechanics", Dover Publ.
 
  • #5
DrDu said:
They are not equivalent, see Landsberg, "Thermodynamics and statistical mechanics", Dover Publ.

which chapter?
 
  • #6
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 :rofl:

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".
 
  • #7
Jobrag, were you at Sussex? My lecturer there used those exact phrases. His name was John Barrow.

Mat
 
  • #8
I had a lecturer who said that to. I think it's fairly common.
 

What is the Third Law of Thermodynamics?

The Third Law of Thermodynamics states that the entropy of a perfect crystal at absolute zero temperature is zero.

What is the significance of the Third Law of Thermodynamics?

The Third Law of Thermodynamics provides a reference point for measuring the entropy of a system. It also helps in understanding the behavior of materials at low temperatures and in predicting the stability of different phases of matter.

How does the Third Law of Thermodynamics relate to the other laws of thermodynamics?

The Third Law of Thermodynamics is closely related to the other two laws of thermodynamics. It provides a logical starting point for the calculation of absolute entropies and relates the concept of entropy to the concept of absolute zero temperature.

What are some real-world applications of the Third Law of Thermodynamics?

The Third Law of Thermodynamics has various applications in fields such as materials science, chemistry, and physics. It is used to understand the behavior of materials at very low temperatures, in predicting phase transitions, and in studying the properties of superconductors and magnets.

Can the Third Law of Thermodynamics be violated?

No, the Third Law of Thermodynamics is a fundamental law of nature and cannot be violated. It is a consequence of the laws of quantum mechanics and is supported by numerous experimental observations.

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