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## Wednesday, 6 July 2011

### Collisions with container

One can calculate the number of atomic or molecular collisions with a wall of a container per unit area per unit time.
Assuming an ideal gas, a derivation[2] results in an equation for total number of collisions per unit time per area:
$A = \frac{1}{4}\frac{N}{V} v_{avg} = \frac{n}{4} \sqrt{\frac{8 k_{B} T}{\pi m}} . \,$

### Speed of molecules

From the kinetic energy formula it can be shown that
$v_{rms}^2 = \frac{3RT}{\mbox{molar mass}}$
with v in m/s, T in kelvins, and R is the gas constant. The molar mass is given as kg/mol. The most probable speed is 81.6% of the rms speed, and the mean speeds 92.1% (distribution of speeds).