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## Main Question or Discussion Point

**Are the RMS-speed of gas particles related to degrees of freedom?**

I give up! I must consult help no matter how embarrassing it is!

Any help is greeted with a big smile!

Does the formula for root mean square speed of particles in a gas (below) apply for all particles?

[tex]v_{rms}=sqrt{frac{3k_{b}T}{m}}[/tex]

I understand that it's derived from the kinetic energy of monatomic gases:

1) [tex]E_{k}=\frac{3}{2}k_{b}T[/tex]

2) [tex]\frac{1}{2}mv_{rms}^2=\frac{3}{2}k_{b}T[/tex]

3) [tex]v_{rms}=\sqrt{\frac{3k_{b}T}{m}}[/tex]

However, the formula of the kinetic energy of diatomic gases is (from Cappelen's "Rom Stoff Tid: Fysikk 1"):

[tex]E_{k}=\frac{5}{2}k_{b}T[/tex]

Thus the RMS speed must be:

[tex]v_{rms}=\sqrt{\frac{5k_{b}T}{m}}[/tex]

No?

Monatomic particles have three translational degrees of freedom, diatomic particles have three translational and two rotational (as they are linear and the rotation around the axis that pierces both particles are "freezed out"), oui?

Is this what is reflected in their formulas for kinetic energy?

The research and lack of sleep resulted in this conclusion:

[tex]v_{rms}=\sqrt{\frac{D_{f}k_{b}T}{m}}[/tex]

Where [tex]D_{f}[/tex] stand for degrees of freedom

So the RMS speed for carbon dioxide in 23[tex]\circ[/tex]C must be:

[tex]v_{rms}=\sqrt{\frac{5 \times\ 1.38\ \times\ 10^{-23} \ J \ K^{-1} \times\ 296K}{44 \times\ 1.66 \times\ 10^{-27} \ kg}}[/tex]

5 degrees of freedom comprising three translational, two rotational (linear molecule) and 0 vibrational as they are negliguble at room temperature.

[tex]v_{rms}=530\frac{m}{s}=1900\frac{km}{h}[/tex]

Now, I will be very happy for any feedback (link to a site or anything) on whether my reasoning or calculation is correct or wrong.

~~~~ Thymo

PS: This is not homework, I'm in first grade physics.

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