Physical and Chemical Changes

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0:05\f0\fs28 \cf0 Hi. It's Mr. Andersen and today I'm going to be talking about changes. These

0:10changes are physical and chemical changes. And students sometimes struggle telling the

0:16difference between chemical and physical changes. And teachers love to kind of ask you hard

0:20questions like, let's see. If water is boiling is that a physical or chemical change? Or

0:26if a moth ball vaporizes over years, is that a physical or a chemical change? Or if you

0:32mix vinegar and baking soda, is that a physical or chemical change? So hopefully by the end

0:36I'll give you a few clues that will allow you to answer that. This picture, I decided

0:40to start with this picture right here. I live in Montana and so in Montana the burgers that

0:45we have our pretty good. The steak that we have is really good in Montana. But we don't

0:49have In and Out Burger. And whenever I go to California I love to get a nice In and

0:54Out Burger. Because the fries are perfect. Get a shake. Oh my goodness. I'm already getting

0:59hungry. But when I eat that burger, that burger is going to go through two changes. The first

1:04changes it's going to go through are physical. In other words, I'm going to start chewing

1:08up that burger and making it into smaller little bits. And then it's going to go through

1:14my digestive system and I'm going to start to chemically breakdown that burger. Now the

1:18cool thing about a burger is that that burger will eventually will become you. In other

1:27words the amino acids that are in a burger are going to be broken down. And then we're

1:32going to use them up inside our body to actually build up the proteins inside our body. And

1:36so it's important that you understand chemical and physical changes and the difference between

1:40them because you need to understand how you are made from a burger. Okay. So let's get

1:45started. Let's start with physical changes. My definition for physical changes occur when

1:50the appearance changes the the substance does not. And so if we were to look at this pen

1:54for example, is it undergoing change? You'd say no. It's not changing at all. But let's

2:01say that this pen were to change it's appearance but it were still to be the parts of a pen.

2:06That would be a physical change. And so how could that happen? Well if we were to heat

2:10this pan up and so it were to melt slightly, it still would be a pen. If we were to break

2:17it in half or bend it, it would still be a pen. In other words, as long as it doesn't

2:21combine with another chemical, as long as that substance stays the same, it's a physical

2:27change. In other words if you start with something like water and we go from water that is say

2:33a solid, like in this down here. And then we end up with water that is a, let's say

2:39a liquid. In other words it starts to melt. Or even if it's H2O that forms a gas, a lot

2:45of this H2O inside this ice is actually going to sublimate. So it's going to vaporize and

2:49turn into a gas. Well it's still H2O. And so it's going to be a physical change at each

2:54of those points. And so here are some things on the side that I said you could check off

2:58if it's a physical change. If it's just melting. If it's boiling. I think I have a picture

3:03of that. So if we're boiling water, this always blew me away as a teacher. A lot of people

3:09don't know why water boils. In other words they say okay you heat it up and it's going

3:15to boil. But they don't know what's inside the bubbles inside boiling water. And so what

3:21is inside the bubbles inside boiling water? Well it's not hydrogen and oxygen gas. That

3:27would be bad. Because if it was hydrogen and oxygen gas, hydrogen and oxygen gas once they

3:32come out would quickly combust. Hydrogen's going to combust and explode. And we know

3:37that doesn't happen. And so what's actually in the bubbles in boiling water? It's simply

3:41water vapor. In other words it's water that is in the state of a gas. And so we would

3:46say not a chemical change. That's a physical change. Or if we were to for example break

3:53these bricks in half or keep breaking these bricks in half and half and half and half

3:57and half and they're still bricks. Then we call that physical. Or let's say we were to

4:03cut things in half. So if we were to use this torch and cut this metal in half, the metal

4:08here and the metal here would still be the same. And so we'd call that a physical change

4:14to this pipe. Now right along the point at which you're cutting, if we combine that with

4:19oxygen, right along that edge, then it's going to be oxidized. So we call that a chemical

4:23change. And then another tricky one that science teachers like to trick you up with is dissolving.

4:29In other words if I were to take a little bit of sugar and add it to this tea as that

4:36sugar dissolves in other words, as it goes from this solid to a more surrounded by water

4:42kind of a state, we wouldn't call that a chemical change. We'd call that a physical change.

4:46And so it's not a chemical change. And if it's physical change then we don't have any

4:50kind of a chemical reaction taking place. And we don't have a formula. We simply have

4:54a change in its state. Or a change in its appearance. And so there's a lot of stuff

4:58that's not really a chemical change. So let's get to what a chemical change actually is.

5:03Chemical change is when you have a substance that changes. And so for example if we go

5:07back to water again. If I were to breakdown water into its gases, H2 and O2, then you'd

5:16know that I don't have a water anymore. I have a hydrogen gas and I have oxygen gas.

5:21And so we'd know that a chemical change has occurred. In other words the substance on

5:25one side yields, that's what this sign means, yields two new substances on the right. And

5:31these would be the products over here. And so we'd say a chemical change has occurred.

5:35Now what are some clues that tell us a chemical change has occurred? Maybe it produces bubbles.

5:39And so this right here is mixing acetic acid with sodium bicarbonate. Otherwise known as

5:45mixing baking soda with vinegar. And what we're getting is bubbles forming. And those

5:49bubbles are going to be a new gas. Now you might be confused thinking, yeah but you just

5:54talked about boiling water and how once that turns into bubbles then it's a physical change.

5:58Well think about it. Did we have bubbles inside the vinegar? Did we have bubbles inside the

6:03sodium bicarbonate? No. And so we've created something new. We've created a gas and that's

6:08what's actually forming the bubbles. And that's what makes the volcano explode when you did

6:11this in elementary. Let's say we mix two chemical together. So you've got chemical A and chemical

6:17B. And we mix one chemical in the other one which normally was clear. And it starts to

6:22get kind of cloudy. So we'd say a chemical change is probably occurring. If we ever have

6:27clouds showing up, either cloudy liquid or clouds in the air that usually just means

6:32a new particle is being formed. And so you know a chemical is being formed. Okay let's

6:36say we get a temperature change. A temperature change is going to indicate a chemical reaction

6:41is taking place. And so the simplest one would be like in methane. Methane is natural gas.

6:46It's in a bunsen burner. And so when we combine that with oxygen, O2 gas, we get some carbon

6:53dioxide. We get some H2O. And we get a lot of energy. And so we're creating energy or

7:00giving off energy that was stored in the chemical bonds of the methane. And so we would call

7:04that a chemical change. In other words we've increased the temperature. So this right here

7:10is pretty cool. We've got two different salts that are probably burning in alcohol. And

7:15they're giving off colors depending on what kind of atoms they are. And we would call

7:19that a temperature change. The salts by themselves are white. And then as we add enough energy

7:25you get combustion with the oxygen. And so this is how fireworks are formed. We have

7:29salts that are mixed up and then we give them combustion or enough of an oxidizer and we

7:35can get all of these different colors. So color change would indicate that we've got

7:38a chemical change going on. And then the last one that would indicate that we have a chemical

7:43change is if we've got. Oh, here's a cool one. This is bioluminescence. This is adding

7:49a couple of chemicals that actually glow. And so we see this in life a lot. For example

7:54we've got jelly fish that can produce this glowing protein. So that's chemical reaction.

7:58We're mixing chemicals and giving off light. And the last one that I was trying to get

8:03to is bread. If you've ever smelled baking bread, there is a chemical change that is

8:09going on inside the bread. So all the products by themselves didn't smell that way, but we

8:13mix them together. We get chemical reactions going on. And so we've got a smell or a change

8:18in state. Now tasting bread is totally safe. But tasting chemicals in the lab is not so

8:23safe. And so I would stay clear of that. This would be a sparkler. And so what do you think?

8:29Chemical change? Physical change? Yeah. That would be chemical. Or going back to a couple

8:34of those answers at the beginning that I posed. What about boiling water? Chemical or physical?

8:39Right answer would be physical. Or what about taking moth balls that you put in your drawer

8:44to keep the moths off from eating your sweaters? If that vaporizes over time, what's that going

8:50to be? It's going to be a physical change. Okay. And so the last thing I want to leave

8:55you with is if we ever have a chemical change then we have a chemical reaction. And so in

9:02a chemical reaction you're taking these things which are the reactants. This would be the

9:06first reactant. The second reactant. And then we're making products from that. So if we

9:10mix hydrogen gas and oxygen gas and create water, then we've had a chemical change. And

9:16we usually have to add a little bit of energy to that. Now you should know this. The reactants

9:20are on the left side. The products are on the right side. And this arrow stands for

9:23the word yields. And so if I were to sketch this out for a second. Let's do the hydrogen.

9:29Hydrogen is going to look like this. Hydrogen is two hydrogen molecules attached together.

9:36And so this 2 right here, this is called the subscript, that tells me there are 2 atoms

9:39of hydrogen in a molecule of hydrogen. This 2 in the front means that we have two molecules

9:47of that. And so on the left side we've got two molecules of hydrogen gas on the side

9:54but each of those molecules are made up of 2 atoms of hydrogen. If we look over here

9:58at the oxygen. Oxygen, I'll draw that a little bit bigger, oxygen attached to itself, there's

10:04two oxygen atoms but there's only one molecule of that. And so now let's look at the product.

10:09Well if we look at the product over here on the right side, we're going to have one water.

10:14So water looks like this. It's got a hydrogen and a hydrogen. It's got another water here.

10:20Hydrogen, hydrogen. And so if we count them up we should have the same if it's a balanced

10:26equation. So how many hydrogens do I have on the left side? 1, 2, 3, 4. How many hydrogens

10:32do I have on the right side? 1, 2, 3, 4. So that's balanced. If we look at the oxygens

10:38on the left side we've got 1, 2. Oxygens on the right side we've got 1, 2. And so that's

10:43a balanced equation. And so I've got a podcast on balancing equations. So you can take a

10:48look at it if you don't know how to do that. The key thing is that you can always change

10:51the coefficients. This would be a 1 right here. You can always change what comes before

10:56the formula, but you can never change the subscripts. Because if you're changing the

10:59subscripts, it would be like breaking that oxygen in half. And we know that that doesn't

11:03occur. So I hope that's helpful. Those are chemical and physical changes.}