[DEMO] Compressibility and Pressure

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From the course by Duke University

Introduction to Chemistry: Structures and Solutions

73 ratings

Duke University

Introduction to Chemistry: Structures and Solutions

73 ratings

This is an introductory course for students with limited background in chemistry; basic concepts such as atomic and molecular structure, solutions, phases of matter, and quantitative problem solving will be emphasized with the goal of preparing students for further study in chemistry.

From the lesson

Phases of Matter, Gas Laws

<p>Welcome to week 4! This week we will discuss phases of matter, the importance of thermal energy, ideal gas law calculations, kinetic molecular theory of gases. Hope you will enjoy!</p> <p>We are at the midway point in the course! As a group you have been watching videos, completing quizzes, and/or actively discussing chemistry on the forums, so please accept our compliments on your hard work so far in the course. </p>

[DEMO] Compressibility and Pressure7:09

[DEMO] Gas Phase14:58

Meet the Instructors

Prof. Dorian A. Canelas
Assistant Professor of the Practice
Chemistry

[MUSIC]

[BLANK_AUDIO]

Let's conduct demonstrations to look more closely at some observable

differences between the solid, liquid, and gas phases of matter.

First, Dr. Lyle has a piece of solid wood in a large syringe.

He's going to push on the plunger of the

syringe to see how far he can push it down.

Is he able to push the plunger down very far?

Is the solid wood compressible?

[BLANK_AUDIO]

Thank you for submitting your answer.

Solids, as you could observe, are not compressible.

Next, he has a greenish-yellow liquid in the syringe.

Again, he's going to push on the plunger of the

syringe to see how far he can push it down.

The end of the syringe has been closed off,

so that the liquid doesn't come out of the syringe.

Is he able to compress the liquid?

Thank you for submitting your answer.

He pushed down as hard as he could, but the liquid was not compressible.

So the volume that could be measured by

the hash marks on the syringe stayed the same.

Finally, he has filled his syringe this time

with air, which is a mixture of gasses.

Just as in the last two times, the end of the syringe

is sealed, so the gas inside the syringe won't be able to escape.

Let's see if he can compress the gas.

Is he able to push the syringe down this time?

Thank you for answering that question.

Gases are compressible.

Dr. Lyle noted that it was easy to push it at first.

But it got harder and harder to push down as the volume decreased.

This is what a man named Boyle figured out.

As the volume in the syringe got smaller, the pressure

with which the gas pushed back on the plunger became greater.

Let's continue with some observations of

one of my favorite substances carbon dioxide.

Dry ice is the solid form of carbon dioxide.

Dr. Lyle is holding a large piece here with a pair of tongs.

It looks like smoke is coming off of it, doesn't it?

Is that really smoke?

[BLANK_AUDIO]

Thank you for submitting your answer.

Hopefully you remembered from earlier experiments

that dry ice is extremely cold.

So we are observing water vapor in the air, condensing into a fine mist or fog.

Little tiny droplets of water.

Next, let's review what happens when dry ice, which is the solid

form of carbon dioxide, is put in different types of closed containers.

First, Dr. Lyle is putting a piece of dry ice in a flexible container, a glove.

He's going to tie the glove closed.

The dry ice is subliming.

Which means it's turning directly from a solid into a gas.

The gas can't escape, because the glove has been tied shut.

As more gas molecules form, the collisions of the gas with the inside

wall of the glove will cause the volume of the glove to increase.

We can also observe this phenomenon when we place the dry ice in

a side arm flask with a balloon tethered to the side arm opening.

Dr. Lyle is putting a stopper on the top

of the flask, so that it is tightly sealed.

We can observe the balloon inflating.

Because the dry ice is going through

a sublimation process and turning into a gas.

So, as the amount of gas increases, the frequency of

the gas molecules hitting the glass walls of the container increases.

This causes the pressure to increase.

That, in turn, causes the volume of the balloon to increase.

What will happen if we put the dry ice in a sealed container

that cannot expand to accommodate the growing

volume of the gas inside the container?

This time, Dr. Lyle is putting the piece

of solid dry ice in an empty film canister.

Again, the dry ice is very cold, so he is handling it with tongs.

He's going to cap the film canister with a solid piece of plastic.

And put it inside the chamber.

The dry ice is turning into a gas through the process of sublimation.

So the number of molecules of carbon

dioxide gas will rapidly increase at room temperature.

As the amount of gas increases through this

process, the number of collisions the gas molecules make.

With the sides of the container and underside

of the top of the container continue to increase.

But the container is ridged this time.

So the volume of the container remains constant.

This causes a build up of pressure.

What do you think is going to happen?

Thank you for submitting your answer.

Let's keep watching this container.

Wow, this is the most boring demonstration ever.

Nothing is happening.

[LAUGH] Just when you least expect it.

Eventually, enough pressure builds up to create a force

needed to pop the top off of the container.

Let's watch the exciting part of this demo replay again.

[BLANK_AUDIO]

I hope you enjoyed an initial look at some of the properties of the phases of matter.

Tune in to the next demonstration to

continue observing gases at different pressures and temperatures.

And this time, we'll get to play with liquid nitrogen.

[BLANK_AUDIO]

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