>> host: The students
in our classroom have been
examining physical changes,
phase changes
and intermolecular forces.
Some great examples of
phase changes can be shown with
the use of liquid nitrogen.
And to help demonstrate,
I've got a special guest
from Atlanta's Fernbank
Science Center, Adrian Elliot.
Thank you so much
for joining me, Adrian.
>> Adrian: Thank you
for having me.
>> host: Nitrogen is in
its' gaseous phase
at room temperature.
If we cooled Nitrogen
to its condensation point,
which is - 196 degrees Celsius,
we'd have liquid Nitrogen.
Now we're going to do
a really cool demonstration
with Mr. Elliot's help.
So, tell me what we're
looking at here?
>> Adrian: Here we have
liquid Nitrogen.
Like you said, its temperature
is negative 196 degrees Celsius.
It is cold, but it boils
at normal room temperature.
>> host: Okay, that's boiling.
Now, do we need to be nervous
about the fumes that are
coming off of that?
>> Adrian: Not at all.
Nitrogen just happens to be
the most abundant gas
in the atmosphere, at 78%.
>> host: Of course.
Now, that's really cool,
but what else can you show us?
What can we see about phase
changes and liquid Nitrogen?
>> Adrian: I'm glad
you asked. Here we have a metal
bowl and some warm water.
This will help us show
a very important phase change.
>> host: Okay.
>> Adrian: Let me pour
a bit of the liquid nitrogen
in here, and let's observe.
>> host: Wow! Look at that!
Now, what are we seeing here?
>> Adrian: This is the
phase change, condensation.
Here we have cold Nitrogen
boiling up together with--
taking some cold water, but
once it touches warm water,
the vapor in the air,
it slows down those particles
to produce small droplets
of water. These small
droplets of water will appear
as white cloud, this
white cloud that we see.
And it's very dense,
as you can see as it falls
off the table.
>> host: So, we're
seeing the phase change
from gas to liquid.
>> Adrian: Correct.
>> host: That's very exciting.
Now, I've noticed you got
several things over here
to-to show us a few more
phase changes.
What have you got for us?
>> Adrian: Well,
what I'm gonna do is move
this across to the side
so we have a little bit
more room to play with.
And, I'm gonna hand
these two to you.
>> host: Okay.
>> Adrian: A banana.
And, I'm gonna put this
into the liquid Nitrogen here.
>> host: Just right in here?
>> Adrian: Yes, please.
>> host: Okay.
>> Adrian: Good job!
>> host: Well, I'm very
excited to see what happens,
but I'm very impatient.
Do you have anything else
over there that's a little
smaller that might go a little
faster in the liquid Nitrogen?
>> Adrian: Okay, let's add
a few more things.
Here I have a flower
which I will also put in there.
>> host: Okay.
>> Adrian: Now, let me
first of all describe what's
happening with this banana.
This banana consists of solid
particles as well as water,
which is inside of the banana.
>> host: Sure.
>> Adrian: When I place
into liquid Nitrogen at
negative 196 degrees Celsius,
it slows down the particles.
The water has a particular
property which we'll examine.
Here we have a small flower.
We're also gonna put
into the liquid Nitrogen.
>> host: Okay.
I'd like to point out,
you're using tongs, we're
wearing our safety goggles,
we're following
the good lab procedures here.
>> Adrian: Correct.
Now, as we place this in,
it's not gonna take
too long, at all.
>> host: Okay.
>> Adrian: Now,
we're gonna pull it out.
Let's see what happens.
>> host: It looks the same.
>> Adrian: But...
>> host: Look at that!
It totally shatters.
It's the liquid in that has
now turned to solid.
>> Adrian: Exactly.
Within the space of just
a few seconds, the petals
of those flowers have turned
to solid and shatter,
pretty much like glass.
>> host: Now, that gives me
an idea about what
might be happening with
the banana in here, but
I just can't wait to see it.
Do you think it's ready?
>> Adrian: I think
it's ready.
>> host: Okay.
>> Adrian: So, we're gonna
pull this back a little bit,
and what I'm gonna do,
is I'm gonna do this one,
if it's okay with you.
>> host: Sure.
>> Adrian: I'm take it out,
and let's observe what happens
if I hit it gently
on the table.
[cracking]
>> host: Broke right in two.
Totally solid.
>> Adrian: Yes.
At this point, the water also
contained in here, has frozen,
so what do you think has
happened to the cells or?...
>> host: And we have a banana
that we did, what, 20-30 minutes
ago, maybe, and you can see
the long-term results of having
been in that liquid Nitrogen.
We're seeing that
browning there.
>> Adrian: Exactly.
This banana, all it cells
have died, so this browning
indicates that the cells
are no more. So, when you see
your bananas at home
and they're brown,
that's what happens.
>> host: Very interesting.
Now, I'm curious.
You've brought some balloons
with you of all kinds.
What are we gonna see
with the balloons?
>> Adrian: Okay.
We'll move this to the side
right here.
Okay, just let that go.
Now, with these balloons,
I have brought an orange one.
>> host: Uh-hmm.
>> Adrian: And, let me
first explain what's inside
of this balloon.
Here we have air.
And the air is basically having
a lot of kinetic energies,
hitting on the inside
of the balloon.
What would happen if I were
to take this balloon
and put it into Nitrogen?
We're gonna investigate.
But before we do that,
there's something students
enjoy seeing.
I know this is for High School--
>> host: It is.
>> Adrian: Usually,
middle school students enjoy
seeing when I show that a gas
can take any shape
by making a balloon animal.
>> host: Who doesn't love
a balloon animal?
[chuckling]
>> Adrian: Okay,
so I'll go ahead.
So, what I'm gonna do,
to show that this gas in here
can take any shape...
has a lot of kinetic energy,
it moves around constantly,
and what I'm gonna do...
...is make a little puppy,
right here.
>> host: Now, that's impressive.
Good job!
>> Adrian: Okay,
thank you.
Now, what we're gonna do...
I'm gonna take this puppy--
inflatable puppy
and I'm gonna place him
in liquid Nitrogen.
Now, to do that, what I'm
gonna do is take these tongs,
these safety tongs,
and I'm gonna add...
>> host: Important to point out
that no animals were actually
harmed in this investigation.
>> Adrian: So-- Correct.
No animals at all.
So, as we place it in...
it doesn't take that long.
>> host: I hear a lot
of noise in there.
>> Adrian: Now, what
I'm gonna do is take him
out right now...
>> host: Totally, deflated,
but it's... it's not staying
that way.
>> Adrian: Exactly.
Let's observe.
>> host: Look at that.
>> Adrian: When we placed
it in, the gas that possessed
a lot of kinetic energy
constantly moved, and gave
the balloon it's size.
>> host: Uh-hmm.
>> Adrian: But once
we placed it in
the liquid Nitrogen, at
negative 196 degrees Celsius,
we slowed those gas particles
down, and we underwent
a few phase changes.
One, going to a gas to liquid,
which we call "Condensation"
and then a liquid to a solid,
which was freezing.
>> host: Uh-hmm.
>> Adrian: On taking it out,
it went from a solid,
to liquid, to gas,
and increased in side.
But when it was small,
that was because
the atmospheric pressure
in fact, crushed it--
>> host: Right.
>> Adrian: ... So it
was a solid and a liquid.
>> host: Let me put that
in reverse, that process.
>> Adrian: Correct.
>> host: Now, that's-that's
so fascinating, but
it all happened, kind of,
in this canister.
Is there a way that
you can show us what was
going on in there?
>> Adrian: I will.
Here we have just one
of these long balloons again,
but here, what I'm gonna do
is place this balloon
into the Nitrogen, and let's
observe what happens.
Let's take a look at it.
What's happening?
>> host: Look at that.
You can see it deflating
all the way down.
>> Adrian: It's going
all the way down as the gas
goes from a gas to a liquid
to a solid.
>> host: That atmospheric
pressure again.
>> Adrian: Crushes it.
>> host: Right.
>> Adrian: Right.
And on taking it out...
let's observe what happens.
>> host: And again,
it re-inflates.
>> Adrian: It goes from
a gas to liquid to solid.
In fact, you see me here
pouring some of the liquid
to the tip of the balloon--
>> host: You see, yeah!
>> Adrian: And the balloon
is going a lot faster than
it did before. Okay?
>> host: Look at that.
And now, you also have
helium balloons.
What can you show us
with the helium balloons
and liquid Nitrogen?
>> Adrian: The helium
balloons are right here.
What I'm going to do
is first of all, move this
to the side, right here.
And I'm gonna take...
one of these balloons,
and then, I'm going to pour
a bit of Nitrogen on here.
Remember that the gas helium
has a lot of kinetic energy--
>> host: That's why
the balloons are floating.
>> Adrian: Exactly.
And, they're all spread out.
Let's see what happens
if we reduce the temperature
of these gasses inside
of these balloons.
>> host: Okay....
We're watching it deflate,
just like the other balloons.
But will it rise again?
>> Adrian: Let's see
right now.
>> host: Look at that.
As soon as it comes back up
to room temperature,
it's back in the air.
>> Adrian: It's back
in the air again.
>> host: That's great.
>> Adrian: Because before,
we've slowed down
those particles,
brought them together,
it became more dense--
>> host: Uh-hmm.
>> Adrian: ... and then
float, once the gas warms up,
spreads out,
it floats one more time.
>> host: Now, our students
have been learning about
intermolecular forces,
so what does all this
demonstrate to us about
intermolecular forces?
>> Adrian: Well, let's take
a look at what we played
with today.
Here we have water.
>> host: Uh-hmm.
>> Adrian: Here...
we had...
liquid Nitrogen.
The liquid Nitrogen boils
at normal room temperature.
>> host: Mmm.
>> Adrian: The water
does not.
The water's intermolecular
forces, namely hydrogen bonds,
and the liquid nitrogen
has mostly
dipole/diplole interactions
which are quite weak.
>> host: Now, dipole/dipole
interactions is something
that will come up in
a couple of units, so stay
tuned for that.
Just remember that phrase
for now.
>> Adrian: Uh-hmm.
>> host: Now, one more thing
just for fun...
I see you've got a racket ball
over there.
>> Adrian: Yes, I do.
>> host: I'm very curious.
[chuckles]
>> Adrian: Okay, I may need
your assistance with this...
>> host: You've got it.
>> Adrian: What I'm
going to do is take
that racket ball,
and first of all, place it
in the liquid nitrogen.
>> host: Okay.
This is a normal racket ball
that bounces like normal.
Everything we expect from
a racket ball.
>> Adrian: Correct.
And, if this racket ball,
which is usually bouncing.
In fact, I should have
taken it out a little bit more.
You can see it bouncing, right?
>> host: It's already gotten
a little harder.
>> Adrian: Exactly.
Now, let's place it in,
and let's leave it there
just for about a little less
than a minute.
>> host: Okay.
>> Adrian: And, we're gonna
take it out [indistinct]
and see if it bounces.
If it still bounces.
Your role...
will be to use this.
>> host: Oh, my!
This is an important
scientific tool, the hammer.
I'm very excited.
>> Adrian: Exactly.
So...
here we've left it for just
a little while.
Once we reduce the temperature
of these particles,
what happens, the motion
is not gonna be as much
as it was before, so...
let's see what happens
when we take this ball out...
and, what I'm gonna
ask you to do, is to hit
this ball with the hammer.
>> host: Okay.
>> Adrian: And I'm gonna
hold it with these tongs.
Not my hands.
>> host: That's a--
that's a good idea.
My aim isn't that good.
>> Adrian: All right.
Let's take a look at the bounce.
>> host: It's definitely changed
on that front.
>> Adrian: Now, I'm gonna
hold it in place...
>> host: Okay.
>> Adrian: Right here.
>> host: I can't wait.
Let's see what happens.
[crashing]
[host gasping]
>> Adrian: Wow!
>> host: Totally shatters.
That's awesome!
>> Adrian: One perfect hit.
[both chuckling]
>> host: Well, if that doesn't
show phase changes,
I don't know what does.
>> Adrian: Yes, so these
particles are really, really
dense and made the ball
extremely brittle.
>> host: Great!
Well, thank you so much
for joining us.
We've learned so much
about phase changes using
your friend, liquid Nitrogen.
I appreciate you being here.
>> Adrian: Thank you
for having me.
>> host: Now that you've seen
some extraordinary phase changes
in liquid nitrogen, let's go
back to our classroom
so our teacher and students
can show us a phase change
you may have thought
was impossible.
>> professor Now let's look at
a very different phase change
called "Sublimation."
Do you think that a substance
can go directly from
a solid to gas?
>> student: No, it has
to become a liquid first.
>> professor: That's often
the case.
But in some special instances,
a solid can transition into
a gas without becoming
a liquid at all.
That phase change
is called "Sublimation."
Let me ask you guys a question:
What do you see?
>> student: That's dry ice.
>> student: What
anyway?
>> professor: Dry ice
is frozen solid carbon dioxide.
Its freezing point is
minus 78 degrees Celsius.
And what you see is the dry ice
cooling the water vapor from
the room and forming clouds.
Watch when I put this piece
of dry ice into water:
[bubbling]
Now, you see
the bubbles forming?
You're seeing the dry ice
changing directly from
a solid into a gas without
ever entering the liquid phase.
And again, this phase change
is called "Sublimation.
Sublimation occurs when
a solid turns directly
into a gas without going
through a liquid phase.
Now, keep in mind,
there aren't too many examples
of substances that we see
doing this in our everyday life.
But dry ice is definitely
one of them.
>> student: Yeah,
I've seen it at concerts.
>> student: And I think
outdoor ice-cream vendors
use that, as well.
>> professor: Exactly.
And sublimation can even
happen with normal ice
in your home freezer.
See, over time, ice-cubes
get smaller because they're
going through sublimation
as the particles of water
move into the air
without even going through
the liquid phase.
Another substance that
can change directly from
a solid to gas is iodine.
Now, as you can see
in this video, iodine is
a solid purple crystal
at room temperature.
But if you put a small amount
in a beaker and heat it
on a hot plate, it undergoes
a phase change.
As it heats up, think
about what usually happens
when you heat a solid.
>> student: Solids usually
melt into liquids.
>> student: Iodine isn't
melting. It's turning
into a purple gas without
turning into a liquid first.
>> professor: Right!
that is sublimation.
By the way, if we were
sublimating iodine in our
classroom, we'd want to use
a fume hood, so we wouldn't
breathe in the vapors
that are produced.
The fume hood uses special fans
to move vapor outside,
away from the laboratory.
Remember that we always
wannna put safety first.
Now, look at what happens
when they put some ice cubes
in a Florence flask.
Look at the bottom
of the flask. Do you see
the purple crystals forming?
Just like the solid iodine
doesn't turn into a liquid when
heated, the gaseous iodine
doesn't turn into a liquid
when it's cooled.
>> student: So, what do you
call it when a substance
goes from a gas to solid?
>> professor: That's called
"Deposition, and that's what
you see happening as
solid iodine crystals form
at the bottom of the flask.
Deposition occurs when a gas
changes directly into a solid.
It's the exact opposite
of sublimation.
One of the most beautiful
examples of deposition here
on Earth is a formation
of snowflake crystals
and frost.
Snow forms as water vapor
freezes directly into solid
ice crystals on the surface
of tiny particles in the air.
Those of you who are familiar
with planetary science
may also be very familiar
with sublimation.
Now, where, other than on Earth,
can sublimation
or carbon dioxide be seen
in large amounts?
>> student: I remember that Mars
has a polar ice cap made
of solid carbon dioxide.
>> professor: You're right.
And Mars also has a very thin
atmosphere, making it
difficult for liquid to form
on the surface.
So what happens to that
Mars polar ice cap when
it warms up a little bit?
>> student: It goes through
sublimation and changes directly
from a solid to a gas.
That must be why the polar
ice caps change shape and size
depending on the seasons.
>> professor: You got it.
And since comets have a lot
of solid carbon dioxide
and water in them, what happens
as they get close to the sun?
>> student: Oh, is that where
that giant comet tail
comes from?
I've seen those!
>> professor: Exactly!
The comet's tail is partly
made of carbon dioxide gas
being released from sublimation
of solid carbon dioxide.
So, what are the major phases
of matter?
>> student: Solid, Liquid,
and Gas.
>> professor: Good.
And what phase transitions
have we discussed?
>> student: Evaporation...
>> professor: Okay, and now,
what happens in that
phase transition?
>> student: A liquid
turns into a gas.
>> student: The reverse
is condensation.
>> professor: Good...
any others?
>> student: Uh, the other
phase change we discussed
was melting, where a solid
goes into a liquid phase.
The reverse of that phase
transition is freezing.
>> student: We also talked about
how a gas can go straight
to a solid phase...
and that's called deposition.
>> student: The reverse of that
is sublimation. That's where
a solid transitions directly
into the gas phase.
>> professor: Great job.
Those are all the phase changes
or transitions
that we discussed.
>> host:: If you want to learn
even more about phase changes,
go to the tool kit for Unit 2,
where we give you instructions
on how to design and carry out
an investigation, that
demonstrates how intermolecular
forces cause different liquids
to evaporate at different
temperatures.
And you can examine why
some solids melt at lower
temperatures while others melt
at high temperatures.
The phase transitions
you just learned about
are all physical changes.
Whether freezing, melting
or vaporizing, materials still
stay the same chemically.
But you need to learn
about the different ways
that substances
change chemically.
So we'll look at chemical
changes in the next video
on the playlist.
See you there!