How would you guys explain "qualitatively" the theorem of maximum work based on this diagram. (that is when a process is reversible and no entropy change in the universe) I don't really know what the graph means. Let's say it's an ideal gas, (S=LnU+...). The diagram divides the plane in two areas. I need to analyze points in both areas and somehow deduce this theorem of maximum work. I'd be grateful if anybody could help me!