Chapter 13: Gases

CHEMISTRY Matter and Change

Section 13.1 The Gas Laws

Section 13.2 The Ideal Gas Law

Section 13.3 Gas Stoichiometry

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CHAPTER

13 Table Of Contents

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• State the relationships among pressure, temperature,

and volume of a constant amount of gas.

scientific law: describes a relationship in nature that is supported by many experiments

• Apply the gas laws to problems involving the

pressure, temperature, and volume of a constant

amount of gas.

SECTION

13.1 The Gas Laws

Boyle’s law

absolute zero

Charles’s law

Gay-Lussac’s law

combined gas law

For a fixed amount of gas, a change in one variable—pressure, temperature, or volume—affects the other two.

SECTION

13.1 The Gas Laws

Boyle's Law • Boyle’s law states that the volume of a fixed

amount of gas held at a constant temperature varies inversely with the pressure.

P1V1 = P2V2 where P = pressure and V = volume

SECTION

13.1 The Gas Laws

Charles's Law

• As temperature increases, so does the volume of gas when the amount of gas and pressure do not change.

• Kinetic-molecular theory explains this property.

SECTION

13.1 The Gas Laws

Charles's Law (cont.)

SECTION

13.1 The Gas Laws

• Absolute zero is zero on the Kelvin scale.

• Charles’s law states that the volume of a given amount of gas is directly proportional to its kelvin temperature at constant pressure.

SECTION

13.1 The Gas Laws

Charles's Law (cont.)

Gay-Lussac's Law

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

SECTION

13.1 The Gas Laws

Gay-Lussac's Law (cont.)

SECTION

13.1 The Gas Laws

The Combined Gas Law

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

SECTION

13.1 The Gas Laws

The Combined Gas Law (cont.)

SECTION

13.1 The Gas Laws

Boyle’s Law explains which relationship of properties in gases?

A. pressure and volume

B. amount and pressure

C. temperature and volume

D. volume and temperature

SECTION

13.1 Section Check

Atoms are in their lowest energy state at what temperature?

A. 0° Celsius

B. 0° Fahrenheit

C. –100° Celsius

D. 0 kelvin

SECTION

13.1 Section Check

• Relate number of particles and volume using

Avogadro’s principle.

mole: an SI base unit used to measure the amount of a substance; the amount of a pure substance that contains 6.02 × 1023 representative particles

• Relate the amount of gas present to its pressure,

temperature, and volume using the ideal gas law.

• Compare the properties of real and ideal gases.

SECTION

13.2 The Ideal Gas Law

Avogadro’s principle

molar volume

ideal gas constant (R)

ideal gas law

The ideal gas law relates the number of particles to pressure, temperature, and volume.

SECTION

13.2 The Ideal Gas Law

Avogadro's Principle

• Avogadro’s principle states that equal volumes of gases at the same temperature and pressure contain equal numbers of particles.

SECTION

13.2 The Ideal Gas Law

Avogadro's Principle (cont.)

• The molar volume of a gas is the volume 1 mol occupies at 0.00°C and 1.00 atm of pressure.

• 0.00°C and 1.00 atm are called standard temperature and pressure (STP).

• At STP, 1 mol of gas occupies 22.4 L.

SECTION

13.2 The Ideal Gas Law

The Ideal Gas Law • Ideal gas particles occupy a negligible volume

and are far enough apart to exert minimal attractive or repulsive forces on each other.

• Combined gas law to ideal gas law

SECTION

13.2 The Ideal Gas Law

The Ideal Gas Law (cont.)

• 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.

SECTION

13.2 The Ideal Gas Law

The Ideal Gas Law (cont.)

SECTION

13.2 The Ideal Gas Law

The Ideal Gas Law—Molar Mass and

Density

• Molar mass and the ideal gas law

SECTION

13.2 The Ideal Gas Law

The Ideal Gas Law—Molar Mass and

Density (cont.)

• Density and the ideal gas law

SECTION

13.2 The Ideal Gas Law

Real Versus Ideal Gases • Ideal gases follow the assumptions of the kinetic-

molecular theory.

• Characteristics of ideal gases:

– There are no intermolecular attractive or repulsive forces between particles or with their containers.

– The particles are in constant random motion.

– Collisions are perfectly elastic.

– No gas is truly ideal, but most behave as ideal gases at a wide range of temperatures and pressures.

SECTION

13.2 The Ideal Gas Law

Real Versus Ideal Gases (cont.)

• Real gases deviate most from ideal gases at high pressures and low temperatures.

• Polar molecules have larger attractive forces between particles.

• Polar gases do not behave as ideal gases.

• Large nonpolar gas particles occupy more space and deviate more from ideal gases.

SECTION

13.2 The Ideal Gas Law

Which of the following is NOT one of the related physical properties described in the ideal gas law?

A. pressure

B. volume

C. density

D. temperature

SECTION

13.2 Section Check

3.00 mol of O2 at STP occupies how much volume?

A. 30.0 L

B. 22.4 L

C. 25.4 L

D. 67.2 L

SECTION

13.2 Section Check

• Determine volume ratios for gaseous reactants and products by using coefficients from chemical equations.

coefficient: the number written in front of a reactant or product in a chemical equation, which tells the smallest number of particles of the substance involved in the reaction

• Apply gas laws to calculate amounts of gaseous reactants and products in a chemical reaction.

When gases react, the coefficients in the balanced chemical equation represent both molar amounts and relative volumes.

SECTION

13.3 Gas Stoichiometry

Stoichiometry of Reactions Involving

Gases • The gas laws can be applied to calculate the

stoichiometry of reactions in which gases are reactants or products.

2H2(g) + O2(g) → 2H2O(g)

• 2 mol H2 reacts with 1 mol O2 to produce 2 mol water vapor.

SECTION

13.3 Gas Stoichiometry

Stoichiometry and Volume-Volume

Problems • Coefficients in a balanced equation represent

volume ratios for gases.

SECTION

13.3 Gas Stoichiometry

Stoichiometry and Volume-Mass

Problems • A balanced chemical equation allows you to find

ratios for only moles and gas volumes, not for masses.

• All masses given must be converted to moles or volumes before being used as part of a ratio.

SECTION

13.3 Gas Stoichiometry

How many mol of hydrogen gas are required to react with 1.50 mol oxygen gas in the following reaction?

2H2(g) + O2(g) → 2H2O(g)

A. 1.00

B. 2.00

C. 3.00

D. 4.00

SECTION

13.3 Section Check

How many liters of hydrogen gas are required to react with 3.25 liters of oxygen gas in the following reaction?

2H2(g) + O2(g) → 2H2O(g)

A. 2.00

B. 3.25

C. 4.00

D. 6.50

SECTION

13.3 Section Check

Chemistry Online

Study Guide

Chapter Assessment

Standardized Test Practice

Gases

Resources

CHAPTER

13

Key Concepts

• Boyle’s law states that the volume of a fixed amount of gas is inversely proportional to its pressure at constant temperature.

P1V1 = P2V2

• Charles’s law states that the volume of a fixed amount of gas is directly proportional to its kelvin temperature at constant pressure.

SECTION

13.1 The Gas Laws

Study Guide

Key Concepts

• Gay-Lussac’s law states that the pressure of a fixed amount of gas is directly proportional to its kelvin temperature at constant volume.

• The combined gas law relates pressure, temperature, and volume in a single statement.

SECTION

13.1 The Gas Laws

Study Guide

Key Concepts

• Avogadro’s principle states that equal volumes of gases at the same pressure and temperature contain equal numbers of particles.

• The ideal gas law relates the amount of a gas present to its pressure, temperature, and volume. PV = nRT

SECTION

13.2 The Ideal Gas Law

Study Guide

Key Concepts

• The ideal gas law can be used to find molar mass if the mass of the gas is known, or the density of the gas if its molar mass is known.

• At very high pressures and very low temperatures, real gases behave differently than ideal gases.

SECTION

13.2 The Ideal Gas Law

Study Guide

Key Concepts

• The coefficients in a balanced chemical equation specify volume ratios for gaseous reactants and products.

• The gas laws can be used along with balanced chemical equations to calculate the amount of a gaseous reactant or product in a reaction.

SECTION

13.3 Gas Stoichiometry

Study Guide

What does the combined gas law relate?

A. pressure and temperature

B. volume and pressure

C. pressure, temperature, and volume

D. pressure, temperature, volume, and amount

CHAPTER

13 Gases

Chapter Assessment

According to Charles’s law, if pressure and amount of a gas are fixed, what will happen as temperature is increased?

A. Volume will decrease.

B. Volume will increase.

C. Mass will increase.

D. Mass will decrease.

CHAPTER

13 Gases

Chapter Assessment

Equal volumes of gases at the same temperature and pressure contain equal numbers of particles is stated by:

A. Law of conservation of mass

B. Boyle’s law

C. Avogadro’s principle

D. Ideal gas law

CHAPTER

13 Gases

Chapter Assessment

What is the volume of 1.00 mol of chlorine gas at standard temperature and pressure?

A. 1.00 L

B. 18.0 L

C. 22.4 L

D. 44.8 L

CHAPTER

13 Gases

Chapter Assessment

When do real gases behave differently than ideal gases?

A. high temperature or low pressure

B. high temperature or high pressure

C. low temperature or low pressure

D. low temperature or high pressure

CHAPTER

13 Gases

Chapter Assessment

If two variables are directly proportional, what happens to the value of one as the other decreases?

A. increases

B. decreases

C. remains constant

D. none of the above

CHAPTER

13 Gases

Standardized Test Practice

What conditions represent standard temperature and pressure?

A. 0.00°C and 0.00atm

B. 1.00°C and 1.00atm

C. 0.00°F and 1.00atm

D. 0.00°C and 1.00atm

CHAPTER

13 Gases

Standardized Test Practice

One mole of gas occupies how much volume at STP?

A. 1.00 L

B. 2.20 L

C. 22.4 L

D. 33.7 L

CHAPTER

13 Gases

Standardized Test Practice

Which of the following would deviate the most from an ideal gas?

A. gas in a hot-air balloon

B. water vapor from the reaction of gaseous hydrogen and oxygen

C. upper atmospheric gases

D. gases near absolute zero

CHAPTER

13 Gases

Standardized Test Practice

What volume will 3.50 mol of Xe gas occupy at STP?

A. 78.4 L

B. 22.4 L

C. 25.9 L

D. 54.4 L

CHAPTER

13 Gases

Standardized Test Practice

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