Are the gas laws compeletely true?

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Discussion Overview

The discussion revolves around the validity and limitations of the gas laws, particularly the ideal gas law, in describing the behavior of gases under various conditions. Participants explore the implications of intermolecular forces, the applicability of the ideal gas law at different pressures, and the complexities involved in real gas behavior.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants express that the ideal gas law is a simplification that does not account for intermolecular forces, questioning whether these forces become negligible or simply weak.
  • Others mention that while the ideal gas law is useful, it is primarily accurate at low pressures, with more complex models available for higher pressures, such as the van der Waals model.
  • A participant notes that the ideal gas law can still provide reasonable approximations at pressures significantly above one atmosphere, such as in practical applications like measuring air in a bicycle tire.
  • Some contributions highlight the need for caution when applying gas laws to the Earth's atmosphere, which is rarely in equilibrium, suggesting that while the ideal gas law can describe certain behaviors, it may not capture all complexities.
  • Disagreement arises regarding the applicability of the ideal gas law to the atmosphere, with some asserting it describes atmospheric behavior accurately, while others caution against oversimplification.
  • Participants seek resources for further understanding of gas laws, intermolecular forces, and models that provide more accurate approximations of gas behavior.

Areas of Agreement / Disagreement

Participants generally acknowledge that the ideal gas law is a simplification and that it has limitations, particularly at higher pressures and in non-equilibrium conditions. However, there is disagreement regarding its applicability to the Earth's atmosphere, with some asserting it is accurate while others caution against its use in predicting atmospheric behavior.

Contextual Notes

Limitations include the dependence on equilibrium conditions for gas laws, the complexity of real gas behavior, and the influence of intermolecular forces, which are not fully addressed by the ideal gas law.

  • #61
russ_watters said:
No, your claims have gone far beyond that. There is a big difference between saying it is the only tool needed (which no one has claimed) and saying it can't be used at all (which is what you claimed).

I have checked all my posts in this thread and I do not believe I ever said it could not be used at all. I explicitly agreed that it could be used for gas residuals. But not for the whole system, and some other law is required to find out the amount of the gas residue.

It seems to me that whether one can say the ideal gas law applies or does not in this situation is a matter of opinion. I have expressed my opinion, others have expressed theirs. If I have offended anyone by any figure of speech, I apologize. I have to excuse myself from further participation in this debate.
 
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  • #62
voko said:
I have checked all my posts in this thread and I do not believe I ever said it could not be used at all. I explicitly agreed that it could be used for gas residuals. But not for the whole system, and some other law is required to find out the amount of the gas residue.
You said it could not be used at all when dealing with a phase transition. That's the scenario we are discussing:
"...the ideal gas law cannot describe a phase transition at all."

You repeated several iterations of that statement. What you are missing is that the ideal gas law doesn't have to describe the transition itself to provide an insight into what happened in the transition.
It seems to me that whether one can say the ideal gas law applies or does not in this situation is a matter of opinion.
No, it really isn't. Utilizing a particular equation to solve a problem will either give a right answer or a wrong answer (to a certain precision). I provided examples of problems that apply here and you ignored them.

There is very little in science that is a matter of opinion.
 
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  • #63
klimatos said:
Most gas laws require that conditions of equilibrium exist (if not throughout the process, then at least at the beginning and end of it). Since the Earth's atmosphere in never even close to a condition of equilibrium, one must be very, very cautious in trying to apply laboratory-valid gas laws to the free atmosphere.

I have been out of town for the last week, and never imagined the fuss that this simple caution would produce. I was referring to non-equilibrium conditions in the free atmosphere--not in the laboratory. The image I had in mind (but, unfortunately did not specify) was the violent and changeable winds accompanied by condensation that can be found in thousands of thunderstorms that are occurring even as you read this post.

If you have an equation of state that accurately relates ambient pressures (including wind pressures) to temperatures (both at the surface of the condensing droplet and in the air between) that is valid under these circumstances, I would dearly love to see it.

I am not unfamiliar with the ordinary gas laws (Boyle's Law, Charles Law, etc.), which is what I had in mind when I wrote the post. I have just reviewed them, and--sure enough--most of them require conditions of equilibrium to be valid.

What did I say that was so contentious?
 
  • #64
klimatos said:
I have been out of town for the last week, and never imagined the fuss that this simple caution would produce. I was referring to non-equilibrium conditions in the free atmosphere--not in the laboratory. The image I had in mind (but, unfortunately did not specify) was the violent and changeable winds accompanied by condensation that can be found in thousands of thunderstorms that are occurring even as you read this post.

If you have an equation of state that accurately relates ambient pressures (including wind pressures) to temperatures (both at the surface of the condensing droplet and in the air between) that is valid under these circumstances, I would dearly love to see it.

I am not unfamiliar with the ordinary gas laws (Boyle's Law, Charles Law, etc.), which is what I had in mind when I wrote the post. I have just reviewed them, and--sure enough--most of them require conditions of equilibrium to be valid.

What did I say that was so contentious?
See the following reference:
Microphysics of Clouds and Precipitation (Atmospheric and Oceanographic Sciences Library) Paperback
by H.R. Pruppacher (Author) , J.D. Klett (Author)
 

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