Thank you for that nice example, however I believe that my question still persists but perhaps I put it unclearly in my first post.
So, what I basically do not understand is how I can get the entropy in arbitrary pressure and temperature? When I take my physical
chemistry book I can see...
I read this discussion but I am interested in how the entropy is obtained as a function of pressure. Namely, how can you determine a following integral for an ideal gas:
$$S(p) = -\int_{0}^{p} \frac{nR}{p}dp $$
when you need to start from 0 pressure?