Van der waal gas in isothermal free expansion

1. Dec 4, 2006

mewmew

1. The problem statement, all variables and given/known data
A gas obeys the Van Der Waal equation of state. The gas undergoes a free expansion from volume Vi to Vf at a constant temperature T. Find the change in entropy of the gas.

2. Relevant equations
du=Tds-Pdv+mdn

3. The attempt at a solution
I can solve the problem assuming du= 0 but this shouldn't be right. I can't seem to find out how to find out how much heat enters to keep the gas at a constant temperature. Everything shows that for a free expansion q=0, but here this is not the case.

Last edited: Dec 4, 2006
2. Dec 8, 2006

OlderDan

Take a look at this