 What we have here are two balloons. They're the same size and shape balloons. This one just has more air than this one. They're connected by a rubber hose, and I have a pinch clamp separating them, pinching off the air. What I want you to do is to predict what will happen when I open this pinch clamp. Now that you've made your prediction, I'm going to open this and I want you to watch the two balloons. Okay? Equilibrium doesn't necessarily mean equal volumes. I know you've all done this. Remember when you take a balloon right out of a package and you try to blow it up? It's hard, and so you stretch and you stretch. What you're doing is trying to stretch this and make it easier to blow up. What was going on in these balloons is the one that was only slightly inflated. The pressure inside exerted by the balloon itself was great so that when we took away the pinch clamp, the pressure is what was getting equal, not the volume.