Why the statistics for a real gas are not quantum in nature?

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Discussion Overview

The discussion centers around the statistical behavior of molecular gases, specifically why they are described by classical statistics rather than quantum statistics. Participants explore the conditions under which classical statistics apply to gases like H2 and the implications of temperature on the relevant degrees of freedom in statistical mechanics.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants question why molecular gases, such as H2, follow classical distribution statistics despite being composed of indistinguishable particles that could be classified as bosons or fermions.
  • One participant suggests that at room temperature, diatomic gases behave classically, and this is supported by standard texts on statistical physics.
  • Another participant notes that quantum mechanics determines which degrees of freedom are relevant at a given temperature, indicating that at room temperature, vibrational modes of diatomic gases are not significant, leaving translational and rotational modes as the primary contributors.
  • It is mentioned that monatomic gases, like helium, also exhibit classical behavior at room temperature.

Areas of Agreement / Disagreement

There is some agreement that diatomic gases behave classically at room temperature, but the initial question regarding the nature of their statistical behavior remains contested, with differing views on the implications of quantum statistics.

Contextual Notes

The discussion does not resolve the underlying assumptions about the transition from quantum to classical statistics, nor does it clarify the specific conditions that lead to classical behavior in molecular gases.

MichPod
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TL;DR
If the gas molecules are either bosons or fermions, why the gas statistics is classical?
A gas of bosons or fermion particles follows a particular quantum statistics. Then why a molecular gas (say, H2) follows a classical distribution statistics? Is it not the case that the molecules should be indistinguishable one from another and be either bosons or fermions? What is exactly the condition which allows a classical statistics?
 
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MichPod said:
why a molecular gas (say, H2) follows a classical distribution statistics?

What makes you think it does?
 
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PeterDonis said:
What makes you think it does?

Lack of education, I guess. :-)
Case resolved, thank you for the hint.
 
True, and quantum mechanics tells you, which degrees of freedom are relevant at a given temperature. E.g., at room temperature the vibrational modes of a diatomic gas are irrelevant and only the translational and rotational ones play a role.
 
DrClaude said:
At room temperature, diatomic gases behave classically.

So do monatomic gases like He.
 
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