What is the equation for calculating molecular flux for a gas?

[Erubus]

Homework Statement

What is the molecular flux of argon gas, molar mass 18 g/mol, with density 0.73 kg/m3 and temperature 300 K? Answer: 3.6×10^27 collisions/m^2s

Homework Equations

I actually have no idea

The Attempt at a Solution

I can't find any reference to molecular flux in my notes or 2 physics textbooks, an equation would be appreciated.

 

[ehild]

You can read about molecular flux here: http://www.lehman.edu/faculty/dgaranin/Statistical_Thermodynamics/Molecular_theory.pdf
(Number of molecules striking unit surface in unit time.)

ehild

 

[Erubus]

Thank you for the link. If I read it correctly, flux = .25*(N/V)*√(8kT/($\pi$m)

however, the density in the problem is given in kg/m^3 while the equation calls for the density based on the number of molecules, which is not given. It's probably an algebra problem now, but I'm also unsure with what to do with the given molar mass.

 

[ehild]

Thank you for the link. If I read it correctly, flux = .25*(N/V)*√(8kT/($\pi$m)

however, the density in the problem is given in kg/m^3 while the equation calls for the density based on the number of molecules, which is not given. It's probably an algebra problem now, but I'm also unsure with what to do with the given molar mass.

It is easy to get the number density of molecules from the mass density and molar mass.
Molar mass is 18 g/mol=0.018 kg/mol. 1 mol gas contains N_A (Avogadro Number) molecules, so the mass of a single molecule is 0.018/N_A kg.
The mass density is 0.73 kg/m³, so the mass of 1 m³ gas is 0.73 kg. How many molecule is it ?

ehild

 

[Erubus]

Thanks, I got it now.