Frequency of Molecular Collisions

The frequency of molecular collisions can be calculated from the mean free path and the average velocity.

For pressure =mmHg =inHg =kPa

and temperature T=K = C =F,

molecules of diameter x 10^-10 meters

and molecular mass M= amu = kg/mol

should have a mean free path of = x 10^m

which is times the molecular diameter

and times the average molecular separation of
x 10^m.

The corresponding average molecular speed is m/s, giving a mean time between collisions of x10 s and a collision frequency of x10 /s.

Note: Typical molecular diameters are .2 to .3 nm and the average mass for dry air molecules is 29 amu.

Molecular speeds

Mean free path