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Collision frequency

Physics calculation for collisions From Wikipedia, the free encyclopedia

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Collision frequency describes the rate of collisions between two atomic or molecular species in a given volume, per unit time. In an ideal gas, assuming that the species behave like hard spheres, the collision frequency between entities of species A and species B is[1][better source needed] where

is the number of A particles in the volume,
is the number of B particles in the volume,
is the collision cross section, the "effective area" seen by two colliding molecules (for hard spheres, , where is the radius of A, and is the radius of B),
is the Boltzmann constant,
is the thermodynamic temperature,
is the reduced mass of A and B particles.
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Collision in diluted solution

In the case of equal-size particles at a concentration in a solution of viscosity , an expression for collision frequency , where is the volume in question, and is the number of collisions per second, can be written as[2] where

is the Boltzmann constant,
is the absolute temperature,
is the viscosity of the solution,
is the number density.

Here the frequency is independent of particle size, a result noted as counter-intuitive. For particles of different size, more elaborate expressions can be derived for estimating .[2]

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References

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