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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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