Thermodynamic equilibrium

  • Thread starter sachi
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Our question states :

"A system enclosed by an impermeable, adiabatic boundary is necessarily in thermodynamic equilbrium. True or false"

The textbooks only define thermodynamic equilibrium for two systems. I.e systems have to be in thermal equilbrium (same T), and there must be no unbalanced forces acting between them (mechanical eq.) and no chemical reactions occuring (chemical eq.). Also there must be no exchange in matter between systems.

Firstly, are no unbalanced forces or chemical reactions allowed to act between the systems, or within each system as well?

Also, I am not sure how these properties relate to one system on its own. If the system is isolated from surroundings by adiabatic impermeable walls, then it doesn't even have to be in thermal equilibrium with its surroundings (or anything else), and I thought that this was one of the fundamental things about thermodynamic eq. I can see that there may well be unbalanced forces and chemical reaction occuring within the system, so the answer is probably going to be false, but I'm not sure because my understanding of thermodynamic eq. is hazy. I'd also appreciate it if somebody could give me a good book reference or internet link.

Thanks

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Answers and Replies

  • #2
Physics Monkey
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You have your system effectively isolated from the rest of the world, thus you are correct that it doesn't have to be in equilibrium with the outside world. Here is a hint that may help you along: can you find two systems that do have to be in equilibrium?
 
  • #3
Tide
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For your problem you only have to come up with a single counterexample to disprove the claim. Enclose a pot of boiling water covered with ice cubes inside that special membrane. Is the system in thermodynamic equilirbrium? :)
 
  • #4
Physics Monkey
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I'll give you that one, Tide. I took the question to be asking something like: if we wait a while, will an isolated system be in equilbrium? I still think this may be what they are after, but the question is obviously very poorly worded if that's the case. I only suggest this because the problem is rather trivial otherwise, as you point out.
 
  • #5
Andrew Mason
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Tide said:
For your problem you only have to come up with a single counterexample to disprove the claim. Enclose a pot of boiling water covered with ice cubes inside that special membrane. Is the system in thermodynamic equilirbrium? :)
Also, it should be noted that the adiabatic walls simply mean that heat cannot flow into or out of the system. This does not mean that energy cannot flow into or out of the system.

So, you could have such a system in a dynamic state doing work on itself and the surroundings or the surroundings doing work on it. A dynamic system is by definition, not in equilibrium.

AM
 
  • #6
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Maybe its just me, but what the crap does thermodynamic equilibrium mean? What state function does "thermodynamic" actually represent?

My only guess is that the question actually means "a system enclosed by an adiabatic boundry is necessarily at thermal equilibrium T/F"

If this is what the question I would assume the answer is T because thermal equilibrium is established when dS/dU = dS/dU and adiabatic implies an isentropic processes.
 
  • #7
Andrew Mason
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elhinnaw said:
Maybe its just me, but what the crap does thermodynamic equilibrium mean? What state function does "thermodynamic" actually represent?
My only guess is that the question actually means "a system enclosed by an adiabatic boundry is necessarily at thermal equilibrium T/F"
If this is what the question I would assume the answer is T because thermal equilibrium is established when dS/dU = dS/dU and adiabatic implies an isentropic processes.
The problem is that unless the adiabatic process proceeds at an infinitesimally slow pace, there is no thermal equlibrium while the process is occurring, so there is no certain temperature and no way to define entropy.

AM
 

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