# Van der waal gas in isothermal free expansion

## Homework Statement

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.

du=Tds-Pdv+mdn

## 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:

OlderDan
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## Homework Statement

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.

du=Tds-Pdv+mdn

## 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.

Take a look at this