And also, because they're moving at high speeds, they don't feel intermocular attractions, so there's nothing stopping them from exiting into the container, so they can completely expand the container. And that means, on a similar note, different gases will mix completely because there is no inter molecular interactions between any two gas molecules. Now, compare this to liquids and solids, right? If I take the same container of liquid and I spill it into the room, what will happen? Well, they won't escape. They will just create a small puddle and they will stay there, right?