Suppose I have a system under which I have constant temperature and pressure. Now, suppose I have a balloon at some volume one and some volume two. And suppose I have three molecules or three moles on my gas inside my balloon. What if I increase the number of moles to six moles? What will happen to my volume? Well, suppose I take a balloon and I put a liter of water into my balloon, it's going to fill up to a certain volume.