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Degrees of freedom
Intermediate
Independent ways a molecule stores energy.
The independent ways a molecule can store energy: 3 translational, up to 3 rotational, and vibrational modes. A monatomic gas has 3, diatomic 5 (room temperature).
Helium f = 3; oxygen f = 5.
Vibrations are 'frozen out' at low temperature.
In more detail
Degrees of freedom are the independent ways a molecule can store energy: translation, rotation and vibration. Monatomic gases have three, while diatomic gases have five at room temperature.
Real-world uses
- Predicting specific heats of gases from their molecular structure.
- Engineers choose working fluids based on degrees of freedom.
- A diatomic molecule can rotate and vibrate as well as move, so it stores more energy than a single atom at the same temperature.
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Frequently asked questions
Why do diatomic gases have five?
Three translational and two rotational degrees, with vibration usually frozen at room temperature.
Does vibration count at high temperature?
Yes, vibrational modes add energy at higher temperatures.
Why do monatomic gases have fewer degrees of freedom?
A single atom has only three translational degrees of freedom, since it has no internal structure to store rotational energy.
Related topics in Kinetic Theory & Statistical Physics
RMS speed · Mean free path · Collision frequency · Equipartition theorem · Specific heats of gases · Maxwell–Boltzmann distribution