1. The problem statement, all variables and given/known data The books often always present pdV but never Vdp. Why is that? surely it is present in expressions like dE or dG where G is the grand potential. Is it because we don't treat p as a variable? If so why not? For each of these function we can only have 3 variables? So having V and p both as variables would be a bit redundant? If so why?