Compressed gases aren't ideal. Let's consider a gas that's non-ideal only because the volume available to each of the N molecules is reduced because each other molecule occupies volume v. Instead of PV=NKT, we get: P(V-NB)=NKT. Let b=1.2 x 10-28 m3.
Let's look at 3moles of this gas at T=300K starting in 0.001 m3 volume.
1) What's the initial value of the pressure? Pinitial= Pa
2) The gas expands isothermally to 0.002 m3.What's the final pressure? Pfinal= Pa
3) How much work did the gas do in this isothermal expansion? W= J