[Ciubba]

The formula I have for collision frequency is [tex]\frac{v_{rms}}{l}[/tex] , where l is the mean free path. This would simplify to [tex]\frac{\sqrt{\frac{3 R T}{M_{kg}}}}{\frac{R T}{\pi  \sqrt{2} d^2 N_a}} \; \rightarrow \; \frac{\sqrt{6} \pi  d^2 N_a}{\sqrt{M_{kg} R T}}[/tex]

which seems to imply that collision frequency decreases with temperature. How is that possible?

[mjc123]

Your expression for l is wrong. RT should be (RT/P), which equals 1/ρ, where ρ is the molar density. Dimensional analysis should tell you that. At constant density, CF increases as sqrt(T). At constant pressure, CF decreases with temperature as the gas expands and the molecules are further apart.

[Ciubba]

Your expression for l is wrong. RT should be (RT/P), which equals 1/ρ, where ρ is the molar density. Dimensional analysis should tell you that. At constant density, CF increases as sqrt(T). At constant pressure, CF decreases with temperature as the gas expands and the molecules are further apart.

That makes sense, thanks!