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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
mix them together. We get chemical reactions going on. And so we've got a smell or a change
in state. Now tasting bread is totally safe. But tasting chemicals in the lab is not so
safe. And so I would stay clear of that. This would be a sparkler. And so what do you think?
Chemical change? Physical change? Yeah. That would be chemical. Or going back to a couple
of those answers at the beginning that I posed. What about boiling water? Chemical or physical?
Right answer would be physical. Or what about taking moth balls that you put in your drawer
to keep the moths off from eating your sweaters? If that vaporizes over time, what's that going
to be? It's going to be a physical change. Okay. And so the last thing I want to leave
you with is if we ever have a chemical change then we have a chemical reaction. And so in
a chemical reaction you're taking these things which are the reactants. This would be the
first reactant. The second reactant. And then we're making products from that. So if we
mix hydrogen gas and oxygen gas and create water, then we've had a chemical change. And
we usually have to add a little bit of energy to that. Now you should know this. The reactants
are on the left side. The products are on the right side. And this arrow stands for
the word yields. And so if I were to sketch this out for a second. Let's do the hydrogen.
Hydrogen is going to look like this. Hydrogen is two hydrogen molecules attached together.
And so this 2 right here, this is called the subscript, that tells me there are 2 atoms
of hydrogen in a molecule of hydrogen. This 2 in the front means that we have two molecules
of that. And so on the left side we've got two molecules of hydrogen gas on the side
but each of those molecules are made up of 2 atoms of hydrogen. If we look over here
at the oxygen. Oxygen, I'll draw that a little bit bigger, oxygen attached to itself, there's
two oxygen atoms but there's only one molecule of that. And so now let's look at the product.
Well if we look at the product over here on the right side, we're going to have one water.
So water looks like this. It's got a hydrogen and a hydrogen. It's got another water here.
Hydrogen, hydrogen. And so if we count them up we should have the same if it's a balanced
equation. So how many hydrogens do I have on the left side? 1, 2, 3, 4. How many hydrogens
do I have on the right side? 1, 2, 3, 4. So that's balanced. If we look at the oxygens
on the left side we've got 1, 2. Oxygens on the right side we've got 1, 2. And so that's
a balanced equation. And so I've got a podcast on balancing equations. So you can take a
look at it if you don't know how to do that. The key thing is that you can always change
the coefficients. This would be a 1 right here. You can always change what comes before
the formula, but you can never change the subscripts. Because if you're changing the
subscripts, it would be like breaking that oxygen in half. And we know that that doesn't
occur. So I hope that's helpful. Those are chemical and physical changes.}