Physical and Chemical Changes

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Mr. Andersen explains the difference between physical and chemical changes. A brief discussion of chemical reactions and equations is also included.
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Transcript Provided by YouTube:

00:05
hi it’s mr. Andersen and today I’m going
00:08
to be talking about changes these
00:10
changes are physical and chemical
00:13
changes and students sometimes struggle
00:15
telling the difference between chemical
00:17
and physical changes and teachers love
00:19
to kind of ask you hard questions like
00:21
let’s see if if water is boiling is that
00:24
a physical or a chemical change or if a
00:27
mothball vaporizes over years is that a
00:29
physical or a chemical change or if you
00:32
mix vinegar and baking soda is that a
00:34
physical or chemical change so hopefully
00:35
by the end I’ll give you a few clues
00:37
it’ll allow you to answer that on this
00:39
picture I decided to start with this
00:41
picture right here um I live in Montana
00:43
and so in Montana the burgers that we
00:46
have are pretty good the steak that we
00:48
have is really good in Montana but we
00:49
don’t have in-and-out burger whenever I
00:51
go to California I love to get a nice
00:53
in-and-out burger because the fries are
00:56
perfect get shake oh my goodness I’m
00:58
already getting hungry um but when I eat
01:00
that burger that burger is going to go
01:02
through two changes the first changes
01:04
it’s going to go through our physical in
01:06
other words I’m going to start chewing
01:08
up that burger and making it into
01:10
smaller little bits and then it’s going
01:13
to go through my digestive system and
01:15
I’m going to start to chemically break
01:17
down that burger now the cool thing
01:18
about about a burger is that that burger
01:23
will eventually become you in other
01:27
words the amino acids that are in a
01:29
burger are going to be broken down and
01:31
then they’re going to use them up inside
01:33
our body to actually build up the
01:34
proteins inside our body and so it’s
01:36
important that you understand chemical
01:38
and physical changes in the difference
01:39
between them because you need to
01:41
understand how you are made from a
01:43
burger okay so let’s get started let’s
01:45
start with physical changes my
01:47
definition for physical changes occur
01:49
when the appearance changes but the
01:51
substance does not and so if we were to
01:54
look at this pen for example is it
01:56
understand undergoing change we’d say no
01:58
it’s not changing at all but let’s say
02:01
that this pen were to change its
02:03
appearance but it we’re still to be the
02:04
parts of a pen that would be a physical
02:07
change and so how could that happen well
02:09
if we were to heat this pan up and so it
02:12
will
02:12
to melt slightly it still would be a pin
02:16
if we were to break it in half or bend
02:18
it it would still be a pen in other
02:20
words as long as it doesn’t combine with
02:22
another chemical as long as that
02:23
substance stays the same it’s a physical
02:27
change in other words if you start with
02:29
something like water and we go from
02:31
water that is a solid like in this down
02:35
here and then we end up with water that
02:37
it is a let’s say a liquid in other
02:40
words it starts to melt or even if it’s
02:42
h2o that forms a gas a lot of this h2o
02:45
inside this ice is actually going to
02:47
sublimate so it’s going to vaporize and
02:49
turn into a gas well it’s still h2o and
02:52
so it’s going to be a physical change at
02:54
each of those points and so here are
02:56
some things on the side that I said you
02:58
could check off if it’s a physical
02:59
change if it’s just melting if it’s
03:01
boiling and so I think I have a picture
03:03
of that so for boiling water
03:05
this always blew me away as a teacher um
03:08
a lot of people don’t know why water
03:11
boils in other words they say okay you
03:14
heat it up and it’s going to boil but
03:16
they don’t know what’s inside the
03:18
bubbles inside boiling water and so what
03:21
is inside the bubbles inside boiling
03:23
water well it’s not hydrogen and oxygen
03:26
gas that’d be bad because if it was
03:28
hydrogen and oxygen gas hydrogen and
03:31
oxygen gas once they come out but
03:33
quickly combust hydrogen is going to
03:35
combust and explode and we know that
03:37
doesn’t happen and so what’s actually in
03:39
the bubbles in boiling water
03:41
it’s simply water vapor in other words
03:43
it’s water that it’s in the state of a
03:45
gas and so we would say not a chemical
03:49
change that’s a physical change or if we
03:52
were to for example break these bricks
03:54
in half or keep breaking these bricks in
03:56
half and a half and a half and
03:57
and a half and they’re still bricks and
03:59
we call that physical or let’s say we
04:02
were to cut things in half so if we were
04:05
to use this torch and to cut this metal
04:06
in half the metal here and the metal
04:10
here would still be the same and so we
04:12
call that a physical change to this pipe
04:14
now right along the point at which
04:16
you’re cutting if we combine that with
04:19
oxygen right along that edge then it’s
04:22
going to be oxidized and so we call that
04:23
a chemical change and then another
04:25
tricky one the science teachers like to
04:26
trick you up with is dissolving so in
04:29
other words if I were to take a little
04:32
bit of sugar and add it to this T as
04:35
that sugar dissolves in other words as
04:38
it goes from this solid to more
04:40
surrounded by water kind of a state we
04:43
wouldn’t call that a chemical change we
04:44
call that a physical change and so it’s
04:46
not a chemical change and if it’s
04:48
physical change then we don’t have any
04:50
kind of a chemical reaction taking place
04:52
and we don’t have a formula we simply
04:54
have a change in its state or changing
04:56
its appearance and so there’s a lot of
04:58
stuff that’s not really a chemical
05:00
change so let’s get to what a chemical
05:01
change actually is chemical change is
05:04
when you have a substance that changes
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and so for example if we go back to
05:07
water again if I were to break down
05:09
water into its gases h2 and o2 then
05:16
you’d know that I don’t have a water
05:18
anymore I have a hydrogen gas and I have
05:20
oxygen gas and so we know that a
05:22
chemical changes occurred in other words
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the substance on one side yields that’s
05:27
what the sign means yields two new
05:29
substances on the right and these would
05:31
be the products over here and so we’d
05:33
say a chemical change has occurred now
05:35
what are some clues that tell us a
05:36
chemical change has occurred maybe it
05:38
produces bubbles and so this right here
05:40
is mixing acetic acid with sodium
05:43
bicarbonate otherwise known as mixing
05:45
baking soda with vinegar and what we’re
05:47
getting is bubbles forming and those
05:49
bubbles are going to be a new gas now
05:52
you might be confused thinking yeah but
05:54
you just talked about boiling water at
05:55
once
05:56
turns into bubbles then it’s a physical
05:58
change well think about it did we have
06:01
bubbles inside the vinegar did we have
06:02
bubbles inside the sodium bicarbonate No
06:05
and so we’ve created something new we’ve
06:07
created a gas and that’s what’s actually
06:08
forming the bolts and that’s what makes
06:10
the volcano explode when you did this in
06:12
elementary let’s say we mix two
06:14
chemicals together so we’ve got chemical
06:16
a chemical B and we mix one chemical and
06:19
the other one which normally was cleared
06:21
starts to get kind of cloudy so we’d say
06:24
a chemical change is probably occurring
06:25
if we’re ever a clouds showing up either
06:28
cloudy liquid or clouds in the air that
06:31
usually just means a new particle is
06:33
being formed and so a new a chemical is
06:35
being formed okay let’s say we get a
06:37
temperature change a temperature change
06:39
is going to indicate a chemical reaction
06:41
is taking place and so the simplest
06:43
wouldn’t belike in methane methane is
06:45
natural gas it’s in a Bunsen burner and
06:47
so when we combine that with oxygen o2
06:50
gas we get some carbon dioxide we get
06:54
some h2o and we get a lot of energy and
06:57
so we’re creating energy or giving off
07:00
energy that was stored in the chemical
07:02
bonds of the methane and so we would
07:04
call that a chemical change in other
07:07
words we’ve increased the temperature so
07:10
this right here is pretty cool we’ve got
07:11
two different salts that are probably
07:13
burning and alcohol and they’re giving
07:15
off colors depending on what kind of
07:17
atoms they are and we would call that a
07:19
temperature change the salts by
07:21
themselves are white and then as we add
07:24
enough energy you get combustion with
07:26
the oxygen and so this is how fireworks
07:28
are formed we have salts that are mixed
07:30
up and then they would give them
07:32
combustion or
07:33
enough of an oxidizer and we can get all
07:35
these different colors so color change
07:37
would indicate that we’ve got a chemical
07:39
change going on and then the last one
07:41
that would indicate that we’ve got a
07:42
change is if we’ve got oh here’s a cool
07:46
one this is bioluminesce
07:48
since this is adding a couple of
07:49
chemicals that actually glow and so we
07:52
see this in life a lot for example we
07:54
have jellyfish that can produce this
07:55
glowing protein so that’s chemical
07:58
reaction we’re mixing chemicals and
07:59
giving off light and the last one that I
08:01
was trying to get to is his bread
08:04
if you’ve ever smelled the baking bread
08:06
there is a chemical change that’s going
08:09
on inside the bread so all the products
08:11
by themselves didn’t smell that way but
08:13
we mix them together we get chemical
08:14
reactions going on and so we’ve got a
08:17
smell or a change in state now tasting
08:19
bread is totally safe but tasting
08:21
chemicals in the lab is not so safe and
08:23
so I would steer clear of that this
08:27
would be a sparkler and so what do you
08:28
think chemical change physical change
08:31
yeah that’d be chemical or going back to
08:34
a couple of those answers at the
08:35
beginning that I posed what about
08:36
boiling water chemical or physical right
08:39
answer would be physical or what about
08:42
taking mothballs that you put in in your
08:44
drawer to keep your sweaters the moths
08:46
off from eating your sweaters if that
08:48
vaporizes over time what that’s going to
08:50
be it’s going to be a physical change
08:52
okay and so the last thing I want to
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leave you with is if we ever have a
08:57
chemical change then we have a chemical
09:00
reaction and so in a chemical reaction
09:03
you’re taking these things which are the
09:05
reactants this would be the first
09:06
reactant the second reactant and then
09:08
we’re making products from that so if we
09:10
mix hydrogen gas with oxygen gas and
09:12
create water then we’ve had a chemical
09:15
change and we usually have to add a
09:17
little bit of energy to that now you
09:19
should know this the reactants are on
09:20
the left side the products are on the
09:21
right side and this arrow stands for the
09:23
word yields and so if I were to sketch
09:27
this out for a second let’s do the
09:29
hydrogen hydrogen is going to look like
09:31
this hydrogen is two hydrogen molecules
09:34
attached together and so this two right
09:37
here this is called the subscript that
09:38
tells me that there are two atoms of
09:40
hydrogen and a molecule of hydrogen this
09:43
two in the front means that we have two
09:46
molecules of that and so on the left
09:48
side we’ve got two molecules of hydrogen
09:51
gas on the side but each of those
09:54
molecules are made up
09:55
two atoms of hydrogen if we look over
09:58
here the oxygen oxygen I’ll draw that a
10:00
little bit bigger oxygen attached to
10:02
itself there’s two oxygen atoms but
10:05
there’s only one molecule of that and so
10:08
now let’s look at the product well if we
10:10
look at the product over here on the
10:11
right side we’re going to have one water
10:13
so water looks like this it’s got a
10:15
hydrogen and a hydrogen
10:17
it’s got another water here hydrogen
10:21
hydrogen and so if we count them up we
10:24
should have the same if it’s a balanced
10:26
equation so how many hydrogen’s do I
10:27
have on the left side 1 2 3 4 how many
10:31
hydrogen’s do I have on the right side 1
10:33
2 3 4 so that’s balanced if we look at
10:37
the oxygens on the left side we’ve got 1
10:39
2 on the oxygens on the right side we’ve
10:42
got 1 2 and so that’s a balanced
10:44
equation and so I’ve got a podcast on
10:46
balancing equation so you can take a
10:48
look lat if you don’t know how to do
10:49
that the key thing is that you can
10:51
always change the coefficients this
10:52
would be a 1 right here you can always
10:54
change what comes before the formula but
10:56
you can never change the subscripts
10:58
because if you’re changing the
10:59
subscripts you’d be like breaking that
11:01
oxygen in half and we know that that
11:02
doesn’t occur so I hope that’s helpful
11:05
those are chemical and physical changes