Chapter 14: Gas Laws: Pressure, Volume, and Temperature

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Basic Terminology

Review of terms used to describe the properties and behavior of gases.

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Opening thoughts…

Have you ever:

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.

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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 to the number of moles, n, using the molar mass.

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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Boyle’s Law

Boyle’s Law, 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?

A decrease in volume will result in increased pressure.

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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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Charles’ Law

Charles’ Law, 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?An increase in temperature results in increased volume.

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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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Gay-Lussac's Law

Gay-Lussac’s law states that the pressure of a fixed amount of gas varies directly with the temperature when the volume remains constant.

Gay-Lussac's Law (cont.)

The Combined Gas Law

The combined gas law states the relationship among pressure, temperature, and volume of a fixed amount of gas.

Avogadro's Law •Volume of gas is proportional to the amount

(moles) of gas V α n•equal volumes of all gases, at the same temperature and pressure, have the same number of molecules".

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The Ideal GasAn ideal gas is defined as one the

particles of which are point masses, showing no interactions (forces of attractions or repulsions) at all, and all collisions are elastic

The Ideal Gas Law

The ideal gas constant is represented by R and is 0.0821 L•atm/mol•K when pressure is in atmospheres.

The ideal gas law describes the physical behavior of an ideal gas in terms of pressure, volume, temperature, and amount.