# Using the Maxwell distribution laws to prove the collision flux equation

1. Sep 14, 2012

### Bipolarity

I have for a while been trying to understand the setup of this equation in calculating the collision flux of a gas through a given rectangular surface of area A:

Number of collisions in a time interval Δt is $(\frac{N}{V})AΔt\int^{∞}_{0}v_{x}f(v_{x})dv_{x}$ where $f(v_{x})$ is the fraction of molecules with speed in the range $(v_{x},v_{x}+dv_{x})$.

My book explains it by asking to choose a particular velocity and consider the volume inhabited by all the particles which can make the collision however I don't understand why the integral comes in after that.

My book is Physical Chemistry for the Chemical and Biological Sciences by Raymond Chang

Perhaps someone can help me by offering insight into why the integral is done or break the reasoning down into simplier steps?

Thanks!

BiP