Name: 物理和化學變化 (Physical and Chemical Changes)
Uploaded: 2021-01-14T06:48:32.000Z
Duration: 11 min 8 s
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\\f0\\fs28 \\cf0 Hi. It's Mr. Andersen and today I'm going to be talking about changes. These

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

these bricks in half or keep breaking these bricks in half and half and half and half

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

字幕列表影片播放

物理和化學變化 (Physical and Chemical Changes)

physical

substance

molecule

solid