College Physics (4th Edition)

The rms speeds of different molecules are: (e) inversely proportional to $\sqrt{molecular~mass}$
In an ideal gas, the average kinetic energy of the molecules is $\overline{KE} = \frac{3}{2}kT$ Then: $\frac{1}{2}m\overline{v^2} = \frac{3}{2}kT$ $v_{rms} = \sqrt{\frac{3kT}{m}}$ The rms speeds of different molecules are: (e) inversely proportional to $\sqrt{molecular~mass}$