I made a thread on this asking the general question in the other forum, but I don't know how to delete that thread. 1. The problem statement, all variables and given/known data An isothermal expansion from Vi = 10.0 L, Pi = 2.46 atm against a constant external pressure until the Pf = 0.246 atm. How much work is done by the gas in joules? 2. Relevant equations [itex]w=-\int P\,dV[/itex] PV = nRT 3. The attempt at a solution I tried using the work integral, but that P is the external pressure, and that would mean I'm finding the work of the external gas, right? I'm trying to find the work done by the expanding gas, which is positive, correct? So I just used W = nRT ln(Vf/Vi) That gives me a positive work of 5743 J. Is that correct? Thanks.