How would you determine what gas has molecules with the greatest average molecular speed at certain temperature?

Dec 12, 2016

All gases have the same average molecular speed at a given temperature.

Explanation:

This is a fundamental postulate of the Kinetic Molecular Theory of gases:

The average kinetic energy of the molecules is directly proportional to the Kelvin temperature.

KE = 1/2mv^2 ∝ T

$\frac{1}{2} m {v}^{2} = k T$, where $k$ is a proportionality constant.

$v = \sqrt{\frac{2 k T}{m}}$

If the temperature $T$ is constant and the mass $m$ of a molecule is constant, the velocity $v$ must also be constant.

In the animation above, the gas molecules are all at the same temperature.

The massive blue molecules move much more slowly than the others, and the grey molecules move faster, but they all have the same average kinetic energy.