Gas Laws: Pressure, Volume, and Hot Air

A Chemistry lesson for 10th Grade Students created by Warren Merkel

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Introduction

Welcome!

This interactive lesson will introduce three ways of predicting the behavior of gases: Boyle’s Law, Charles’ Law, and the Ideal Gas Law. Never heard of them? Don’t worry– that’s the purpose of this lesson!

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Navigation

Throughout this lesson, you will use buttons at the bottom right corner of the page to navigate.

Takes you to the next page

Takes you to the previous page

Takes you to the Main Menu

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Main Menu

Basic Terminology

Boyle’s Law

Charles’ Law

Ideal Gas Law

Review of all four lessonsReview

Lesson 1

Lesson 2

Lesson 3

Lesson 4

Lesson 1: Basic Terminology

This lesson reviews terms used to describe the properties and behavior of gases.

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Opening thoughts…

Have you ever:

Seen a hot air balloon?

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Opening thoughts…

Have you ever:

Seen a hot air balloon?

Had a soda bottle spray all over you?

Baked (or eaten) a nice, fluffy cake?

These are all examples of gases at work!

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Properties of Gases

You can predict the behavior of gases based on the following properties:

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Pressure

Volume

Amount (moles)

Temperature

Lets review each of these briefly…

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PressureVolume

Amount (moles)

Temperature

You can predict the behavior of gases based on the following properties:

Pressure

Pressure is defined as the force the gas exerts on a given area of the container in which it is contained. The SI unit for pressure is the Pascal, Pa.

• If you’ve ever inflated a tire, you’ve probably made a pressure measurement in pounds (force) per square inch (area).

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Pressure

VolumeAmount (moles)

Temperature

You can predict the behavior of gases based on the following properties:

Volume

Volume is the three-dimensional space inside the container holding the gas. The SI unit for volume is the cubic meter, m3. A more common and convenient unit is the liter, L.

Think of a 2-liter bottle of soda to get an idea of how big a liter is. (OK, how big two of them are…)

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Pressure

Volume

Amount (moles)Temperature

You can predict the behavior of gases based on the following properties:

Amount (moles)

Amount of substance is tricky. As we’ve already learned, the SI unit for amount of substance is the mole, mol. Since we can’t count molecules, we can convert measured mass (in kg) to the number of moles, n, using the molecular or formula weight of the gas.

By definition, one mole of a substance contains approximately 6.022 x 1023 particles of the substance. You can understand why we use mass and moles!

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Pressure

Volume

Amount (moles)

Temperature

You can predict the behavior of gases based on the following properties:

Temperature

Temperature is the measurement of heat…or how fast the particles are moving. Gases, at room temperature, have a lower boiling point than things that are liquid or solid at the same temperature. Remember: Not all substance freeze, melt or evaporate at the same temperature.

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Water will freeze at zero degrees Celsius. However Alcohol will not freeze at this temperature.

How do they all relate?

Some relationships of gases may be easy to predict. Some are more subtle.Now that we understand the factors that affect the behavior of gases, we will study how those factors interact.

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How do they all relate?

Some relationships of gases may be easy to predict. Some are more subtle.Now that we understand the factors that affect the behavior of gases, we will study how those factors interact.

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Let’s go!

Lesson 2: Boyle’s Law

This lesson introduces Boyle’s Law, which describes the relationship between pressure and volume of gases.

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Boyle’s Law

This law is named for Charles Boyle, who studied the relationship between pressure, p, and volume, V, in the mid-1600s.

Boyle determined that for the same amount of a gas at constant temperature, results in an inverse relationship:when one goes up, the other comes down.

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pressure

volume

What does Boyle’s Law mean?

Suppose you have a cylinder with a piston in the top so you can change the volume. The cylinder has a gauge to measure pressure, is contained so the amount of gas is constant, and can be maintained at a constant temperature.

A decrease in volume will result in increased pressure.

Hard to picture? Let’s fix that!

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Boyle’s Law at Work…

Doubling the pressure reduces the volume by half. Conversely, when the volume doubles, the pressure decreases by half.

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Lesson 2 Complete!

This concludes Lesson 2 on Boyle’s Law!

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Click the Main Menu button below, then select Lesson 3 to learn about how temperature fits in.

Lesson 3: Charles’ Law

This lesson introduces Charles’ Law, which describes the relationship between volume and temperature of gases.

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Charles’ Law This law is named for Jacques Charles, who

studied the relationship volume, V, and temperature, T, around the turn of the 19th century.

This defines a direct relationship: With the same amount of gas he found that as the volume increases the temperature also increases. If the temperature decreases than the volume also decreases.

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volume

temperature

What does Charles’ Law mean?Suppose you have that same cylinder with a piston in the top allowing volume to change, and a heating/cooling element allowing for changing temperature. The force on the piston head is constant to maintain pressure, and the cylinder is contained so the amount of gas is constant.

An increase in temperature results in increased volume.

Hard to picture? Let’s fix it (again)!

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Charles’ Law at Work…

As the temperature increases, the volume increases. Conversely, when the temperature decreases, volume decreases.

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Lesson 3 Complete!

This concludes Lesson 3 on Charles’ Law!

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Click the Main Menu button below, then select Lesson 4 to put all the pieces together with the Ideal Gas Law.

Lesson 3 Complete!

This concludes Lesson 3 on Charles’ Law!

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Click the Main Menu button below, then select Lesson 4 to put all the pieces together with the Ideal Gas Law.

Mission complete!

You have completed the lessons and review. Congratulations!

You should now have a better understanding of the properties of gases, how they interrelate, and how to use them to predict gas behavior.

Please click on the button below to reset the lesson for the next student. Thanks!

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