<Dd> l = k B T 2 π d 2 p, (\ displaystyle \ ell = (\ frac (k_ (\ text (B)) T) ((\ sqrt (2)) \ pi d ^ (2) p)),) </Dd> <P> where k is the Boltzmann constant . </P> <P> In practice, the diameter of gas molecules is not well defined . In fact, the kinetic diameter of a molecule is defined in terms of the mean free path . Typically, gas molecules do not behave like hard spheres, but rather attract each other at larger distances and repel each other at shorter distances, as can be described with a Lennard - Jones potential . One way to deal with such "soft" molecules is to use the Lennard - Jones σ parameter as the diameter . Another way is to assume a hard - sphere gas that has the same viscosity as the actual gas being considered . This leads to a mean free path </P> <Dl> <Dd> l = μ p π k B T 2 m, (\ displaystyle \ ell = (\ frac (\ mu) (p)) (\ sqrt (\ frac (\ pi k_ (\ text (B)) T) (2m))),) </Dd> </Dl>

What is the mean free path of a gas molecule
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