 In this video we are going to talk about how material objects can change, which is probably the most general aspect of what chemistry is about. The first type, there are basically two types of, two general types of ways that matter can change. The first type is called physical change, the other type is called chemical change, and we will talk about chemical change in a little bit, but right now we are going to talk about the first general type called physical change. Physical change is when an object or a material changes its shape, but it is still made of the same substance, in other words it is still made of the same molecule or the same molecules or the same atoms. So the classic example of this of a material changing shape is liquid water in a container. So if you have liquid water in a bottle, like we have over here in this picture, the water takes on the shape of the bottle. If you pour your liquid water into a glass, then the water will change its shape into, it will roughly mimic the shape of the glass. So the water going from one container to the other undergoes a physical change, and because it changed its shape, but if you could look carefully enough, the stuff that you just poured into the container is still made of water molecules. They were water molecules in the bottle, and they are still water molecules in the glass. So that is a very general example of what a physical change is, the material changes its shape, but the stuff that it is made of does not actually change. There is a special kind of physical change, so there is something called a change of state, which is a special type of physical change, and what I mean by change of state is sort of illustrated with water again, but it does not have to be water. So an example here, these are supposed to be cubes of ice. This is definitely water, but it is frozen water, and so it is solid, and we can say that this water is in a solid state. If you could zoom in and look at the atoms or molecules in your solid ice, the atoms or molecules are relatively fixed, they are not moving very much, you can think of them as kind of lined up in rows, that may or may not be true, but they are more or less stuck in place. And so this is going to be my cartoon version of a bunch of water molecules, if you could zoom in and look at the water molecules in ice, maybe they would be lined up relatively speaking in somewhat nicely rows, and this is when your water is in a solid state. If you heat up your solid water, it will turn into liquid water, and so you could say that you changed the state of your water from a solid state to a liquid state. This is what I mean when I say that you can change the state of your material. If your material goes from a solid state to a liquid state, that's a change of state, and it's a type of physical change, because this ice over here made of water molecules, so is this liquid water over here also made of water molecules. But the slight difference is that the atoms and molecules, atoms or molecules in your liquid are moving around more compared to how they were moving around when they were solid. So here I have my water molecules, but let's imagine that they're tumbling around, rolling around on top of each other. Then if you heated the liquid water enough, you could turn it into steam, which is a gas, and so you could say that that water isn't a gas state, so you can go from a liquid state to a gas state as well, and that's also a change of state, because this is still made of water molecules, it's just steam now. And so the all two changes, going from a solid state to a liquid state, or a liquid state to a gas state, are examples of changes of state. Here if you wanted to sort of picture the water molecules in steam, they're kind of like the water molecules in liquid water except they're further apart and they're moving around faster and sort of tumbling around faster. So here I have them kind of separated from each other more. I want to also point out, everything that I've shown you at this point has been showing you a change of state, which is a type of physical change. But we've always been going in this direction, solid to liquid, liquid to gas. You can go in the reverse direction. You can take a gas, you can take steam and cool it down, and it will condense into a liquid. You can take a liquid, cool it down, and it will freeze into a solid. So if you go backwards, that's also a change of state as well. You're just changing the physical state, you're changing sort of the shape of the material, but you're not changing what it's made of. It's not just water that does this, pretty much most pure materials that I can think of can do this under the right circumstances. This is supposed to be bricks of gold. This is solid. But even gold, if you heat it up enough, you can turn it into a liquid state. So that's supposed to be liquid gold. And so this is just another example. Going from a solid to a liquid, even in the case of gold, is called a change of state. And you could heat the gold up, the liquid gold up even more. And even that will turn into a gas. So you can change the state of gold or other pure materials as well, in a way that's similar to the way that we can change the state of water. I want to go over some terms. Usually, under the conditions that we are accustomed to, materials go from a solid state to a liquid state if we heat them up. And then if we heat them up even more, they turn into a gas. And these are all examples of changes of state again. You can go backwards. Like I said, you can go from a gas to a liquid. You can go from a liquid back to a solid if you cool things down. Each of these changes has its own special name. If you go from a solid to a liquid, that's called melting. If you go from a liquid back to a solid, guess what that's called? Freezing. If you go from a liquid to a gas, that's called evaporation. And if you go from a gas back to a liquid, it's called condensation. So those, I would like you to know those terms and sort of what's going on under each circumstance. There are some weird things that can happen. Sometimes you can go from a solid directly into a gas. This is also a change of state. But you're skipping over the liquid state. Sometimes this can happen under special circumstances and with special materials. Carbon dioxide gas, the formula for carbon dioxide is CO2. You can actually get frozen carbon dioxide, solid carbon dioxide. If you leave it out, let's say on your kitchen table, it looks more or less like a little cube of ice. But as you warm it up, it doesn't turn into a liquid. It turns directly into a gas. So this is just an example of a material that can go from a solid directly into a gas without turning into a liquid. Going from a solid directly into a gas is its own special fancy name. It's called sublimation. I suppose you need to know that. Honestly, I don't really think you need to know that. But there you have it. Just in case you want to impress people at cocktail parties. If you go from a gas and cool down directly back into a solid, that has its own special name as well. That's called deposition. So there you have it. Now you're much the wiser, I guess. So those are all examples of changes of state. You're basically change of state roughly equals changing the shape of your material without actually changing what the material is made of. The other major type of change other than physical change is something called a chemical change. In a chemical change, there are basically two types of chemical change. The one that we're going to spend a lot of time talking about is when the atoms in the molecule actually rearrange who they are attached to. There's a slightly different type of chemical change when one type of atom turns into a different type of atom. But we're not going to talk about this until much later in the course when we talk about nuclear radiation. So this is a type of chemical change. But we're not going to talk about it at the moment. Mostly we're going to focus on when the atoms in a molecule rearrange who they're attached to. That's a type of chemical change. This chemical change is illustrated in this cartoon here. I have two molecules on the left side of my arrow. See my arrow here. And my two molecules on the left side, they basically each consist of three atoms. A big blue one always attached to two little red ones. Another big blue one always attached to two little red ones. If I do some magic or put these two molecules under certain conditions, I can basically rip the red atoms off of the blue ones and attach them to each other. In other words, I can rip the red ones off of the blue ones and turn them into that over there on the right. I can rip the blue ones off of the red ones and attach them to each other and make this molecule over here on the right. If I do that, if I rearrange the attachments, if I start ripping atoms off of each other and reattaching them, that's called a chemical change. So this is kind of my cartoon example of a chemical change at the moment. There are many other types of chemical changes. This is just one specific example.