 What's the difference between a solid, a liquid, and a gas? Think of these balls as atoms or molecules. And here we have a nice orderly structure as in a solid. If we add energy, the molecules vibrate, but they stay in relative position. So there's kinetic energy, their motion. If we increase that kinetic energy and give them more motion, and now we have a liquid, we have even more energy. Let's suppose we have a liquid that is a mixture of two compounds. Let the white golf balls represent ethanol, and the blue represent water. And we want to separate them. At this point, you see there are 18 white ethanol molecules and only four water molecules. So we're going to heat this up, add energy to it. So as we add energy, some of it is going to evaporate and leave our container. All right, after adding a little energy, now we have 2, 4, 6, 8, 10, 12 white balls and four blue balls. So let's try again. Add more energy. All right, now you see there are 2, 4, 6 ethanol and three water molecules. You should note that even though what we're trying to do is remove all the ethanol, we also remove some of the water. So when you're trying to distill something, you're not going to get a 100% pure substance.