# Second Virial Approximation for Infinite Number of Particle Types

1. Apr 2, 2012

### xentity1x

1. The problem statement, all variables and given/known data
Here's the setup. I have a gas of rod like molecules, where n*f(u)*dΩ is the number of rods having their direction in the solid angle dΩ pointing in the direction u. The problem says to consider rods pointing in different directions as separate species.

2. Relevant equations
I know the second virial approximation to the free energy is of the form $F=F_{ideal}+\int \int d\Omega d\Omega'B(u,u')f(u)f(u')$. I'm supposed to find Fideal

3. The attempt at a solution
I'm a little confused about how to start. I thought finding the partition function for one particle type by considering the volume excluded by all the other particle types. I'm not sure what the excluded volume would be. Would it depend on the angle between the particle types?