The root-mean-square speed of ideal gas molecules of molar mass $M$ at temperature $T$ is:

The mean free path increases as the number density of gas molecules decreases.

The formula for the mean free path $\lambda$ in an ideal gas (number density $n$, molecular diameter $d$) is:

The mean free path of a gas molecule depends on:

The molar heat capacity at constant volume $C_V$ for a diatomic ideal gas (ordinary temperatures) is:

The total number of degrees of freedom of a diatomic ideal gas molecule at ordinary temperatures is: