States of matter

0:00- [Instructor] You probably know that if you heat ice, eventually it turns into liquid water and if you continue heating it, it turns into steam. But the question is, what actually happens when ice turns into liquid water or when water turns into steam? Let's find out.

0:17Look around you. There's so much stuff like rocks and trees and lakes, and even invisible stuff like the air. In science, we call this stuff matter. What is matter? Matter is anything that has mass and occupies space. Think about rocks and trees, they have mass, they occupies space, therefore they are matter.

0:40And matter usually comes in three forms. We have solids like the rocks and the trees, and we have liquids like the water in the lake or the lemonade that you might be carrying with you. And we have gases like the water vapor or the gases in the air, the same gases that you breathe in and out.

0:59These are called the states of matter. Now, there are other states of matter as well, but we won't talk about them. These are the most common ones that you find in everyday life. Okay so if you go back to our example, ice is solid, water is liquid, and steam is gas.

1:15But again, coming back to the question, what really happens when you heat something and it changes from say, a solid state to a liquid one? Well, to answer that question, we need to zoom in. If you zoom in to any matter, you'll find that it's made of very tiny particles.

1:35Technically, these particles are atoms and molecules that make up matter, but let's not worry about those names right now. Let's simply think of them as tiny particles. And these particles are incredibly tiny. How tiny you ask. Well, even within a ordinary microscope, you wouldn't be able to see them.

1:52But what's important is that these particles are constantly moving, which means they have energy. This energy of motion is what we call kinetic energy. But when it comes to solids, look, even though the particles are moving and have kinetic energy, they are pretty much locked in place.

2:14They're mostly just jiggling in place, right? That's the defining feature of a solid, because these particles pretty much stay locked in place, solids have a fixed volume and they have a fixed shape. That's what makes a solid a solid. Okay, but what happens if we start heating it up?

2:35Well, when you heat something up, you're transferring energy into it. So the kinetic energy of the particles increases, which means the particles start moving faster. And although we actually can't see this happening with our eyes, we can feel it. It'll have a higher temperature.

2:53When something has higher temperature, it means the particles that make it up have more kinetic energy. That's pretty awesome, right? But anyways, this is still a solid because the particles are still mostly locked in place. But what happens if we continue heating it?

3:09Well, the kinetic energy keeps increasing. The particles move faster and faster, and eventually they move much farther apart. And look, they are no longer locked in place. This is very different from what we saw before. I mean, the particles are still fairly close together, so they still have a fixed volume, but now the particles can move around, meaning it can flow, meaning it no longer has a fixed shape.

3:43We now have a liquid, that's what a liquid is, in liquid, the particles that make it up can move around each other. And the process of turning a solid into liquid is what we call melting. Okay, what happens if we continue heating? Well, the kinetic energy continues to increase.

4:04The particles will move farther and farther apart, and eventually they become so far apart, they are pretty much moving freely. The substance no longer even has a fixed volume. This is now a gas. In gas, the particles are very far apart and move freely in all directions.

4:26Gases neither have a fixed volume nor a fixed shape. And the process of turning a liquid into gas is what we call boiling. So now we have the complete picture. In solids, the particles are pretty much locked in place and they have a fixed shape and volume. If you heat it and increase the kinetic energy, eventually the particles can move around each other, we call this a liquid.

4:55They still stay relatively close to each other, so they have a fixed volume, but it can flow now, so it no longer has a fixed shape. And if you continue heating it, the particles will eventually move so far apart that the substance neither has fixed shape nor volume.

5:13The particles would be moving freely in all directions, we call that a gas. But finally, what do you think would happen if we were to cool matter? What would happen if we cooled this gas? Well, think about it, cooling is basically the reverse of heating. You're now removing energy, so the kinetic energy decreases.

5:31The particles move more slowly, they start coming closer to each other, and if you remove enough kinetic energy, they come close enough together to form a liquid. This process is called condensation, and you've probably seen condensation before. The tiny droplets that form on the outset of a cooldrink, that's condensation.

5:52Water vapor in the air, which is a gas cools down and condenses into liquid water. And what if we cool it even further? Maybe we put the water into a freezer. Now we are removing even more kinetic energy. The particles move even more slowly, come even closer together, and eventually become locked into place.

6:15The liquid freezes into solid. So this process of turning a liquid into solid is called freezing. That's the opposite of melting. And so in general, whenever matter changes from one state to another, we call it a phase change. So melting, boiling, condensation, and freezing, they're all examples of phase changes.