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Question 31086
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Kinetic Theory and Thermodynamics: Quantum Effects MCQ

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Quantum EffectsHardQuestion 31086

Question

At very low temperatures, Cv of diatomic gas approaches 3R/2 (monatomic value) because:
  1. A
    Molecules split into atoms
  2. B
    Rotational modes freeze out below rotation temperature
    Correct
  3. C
    Translational DOF decrease
  4. D
    Pressure increases

Correct answer

Rotational modes freeze out below rotation temperature

Explanation

Quantum mechanics: rotational energy is quantised. At low T, thermal energy kT << rotational quantum → rotational modes not activated. Cv → 3R/2 (only translation).

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