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Ideal theory

  1. Nov 9, 2005 #1
    How did the scientists like Boyle and Avagadro did experiments and still got results, which supported the ideal gas theory? It is actually wrong and still how did they get results that volume is inversely proportional to pressure while temperature directly to pressure. I think the only chance of disproving ideal theory is experimenting. There is no theoretical reason for such a behavior of real gases. Scientists who are considered to be great developed the ideal theory. So I doubt their Excellency if they made mistakes in observations. This is because I learn them to be great scientists. Moreover why is importance given to ideal theory when it is already disproved?
  2. jcsd
  3. Nov 9, 2005 #2
    it still holds for very low pressures and temperatures of gases (see z-factor chart)
    well its still important because it still IS part of the picture with real gases.. just with other added variables
  4. Nov 11, 2005 #3
    I don't when did the Ideal gas theory been disaproved.
    well the reason for such a behavior of real gases is two faulty assumtions made in the kinetic theory of gasses,
    1. Volume of gas molecules is negligibe as compared to the volume of empty space.
    2. No moleculer atraction or repulsion exists.
    both hold good only at low temp and pressure.
    moreover real gases show little deviation than the predicted behavior its not like they completely disobey these laws. i think u must have seen a hot air baloon, what do u think make it fly...its basically inverse propotionallity of temp and volume of a gas at constant pressure.
    well befor doubting their exellency u should doubt ur own inteligence and understanding
  5. Nov 11, 2005 #4


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    Vaisakh : Theoretical physicists now routinely use things known as models. A model is a simple construction that captures all the important physics of a real physical situation. The Ideal Gas model, is one such extremely successful model. By simply treating molecules as non-interacting, pointlike objects, an enormous wealth of knowlegde about the behavior of gases has been extracted. That's the hallmark of an excellent model, not a lousy one !
  6. Nov 12, 2005 #5
    Gokul, it's a serious issue if this question is considered as a violation of physicsforum rules. The alertness is due to certain links shown by you at the bottom of your post. I am anyway asking this sincerely that I want to make clear my misunderstandings about ideal theory and those experiments. I make it clear that I don't wish to violate any laws. I wish to improve my dealings with others. Please advice and a request to forgive if I have done something very much wrong. I don't want to become a violator of any laws in physicsforum.
    Anyway advice me on how to judge whether my post is out of rule or within the rule.

    Jimmy, I thank you for making it clear. Of course what I meant (or more appropriately want to mean) is that the scientists who developed ideal theory are indeed great but I have a misunderstanding about their observations due to my misunderstanding. It is not the other way that I feel what I understood is correct and hence I feel those scientists aren't great. I am not blaming you for you didn't understand what I wanted to mean or what my outlook is from the post, it is because I didn't put it up well enough. I am a person of a policy to respect each individual even if he is wrong if he has logic. Hence I have respect even for those scientists who failed or have given wrong models because they could atleast do so. Infact they were the people who made the first step towards the correct step. Such words like 'doubt their Excellency' were used by me to make clear the intensity of clarity needed for me on the topic and never that I am greater than those scientists nor am I someone to comment on their intelligence.
    A bit on topic-how was it proved that real gases do not behave ideally? What is the reason for the existence of both positive as well as negative values of z? I want to be clear on following aspects. I don't want to google on this simply. I think an expert's advice like yours will help.
  7. Nov 12, 2005 #6
    well i think it should have been the experiments, they must have found that the results were not the same as predicted by the theory.
    And i don't know yet wether negative z is possible, if z = pv/nRT is what you are talking about. But for real gasses z is either >1 or <1.
    If z>1, gas would be less compressible i.e hydrogen, i think. because the size of its atom (molecule, in some case) is small, and possibly lesses intermoleculer intraction. and otherwise for z<1.
    and 'm no expert, 'm just a random kid with opinion of everything who paid attention in high school.
  8. Nov 13, 2005 #7
    vaisahakh... I think your doubt was legitimate... What would be the world if should not be existed men like Bohr! He said something of completely incorrect about hydrogen atom! He won Nobel Prize, but his merit rests for the very good approximation to the truth! He was so close to the target... but nevertheless it was incorrect. Nature is really really complicate!
    If you look at number of Avogadro axcepted in history, you see it got a great range of variability. It depends on how nature is investigated. Indeed on a theoretical point of view, ideal theory is the milestone of many theories in statistical mechanics, i.e. Ising model, in which similarly the system is not interactint in anyone of its subsystem... So you can learn something by dealing with something else!
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