Lesson Plans

Chemistry: The Central Science 9th Edition ©2003

by Brown, LeMay, and Bursten

Week 11: Gases

Chapter 10: Gases

This very important lesson gives students a deeper understanding of the physical properties of gases and the behavior of gas molecules. Gases differ significantly from the other physical states, especially because the volume of a gas depends on conditions.

College Board Performance Objectives:

• Describe properties of gases compared to other physical states.
• Define common units of gas pressure.
• Describe how gases respond to changes in V, n, P, and T.
• Be able to solve problems using combined and ideal gas equations.
• Be able to calculate molar mass from gas density and vice versa.
• Calculate the partial pressure of any gas from the composition of its mixture.
• Understand the process and calculation of the pressure of a gas collected over water.
• Calculate mole fraction from partial pressure.
• Describe how the relative rates of diffusion and effusion of gases depends on their molar masses.
• Understand the kinetic molecular theory.
• Be able to work through gas stoichiometry problems.
• Understand that real gases deviate from ideal gases especially at high pressure and/or low temperature.
• Know the real gas equation, with corrections for particle attraction and size.

College Board Lab Objectives:

• Observe how gas volume and pressure are determined in the lab and how the gas volume is affected by temperature and pressure.
• Observe how well real gases behave ideally at normal conditions and determine the universal gas constant.

Suggested Labs:

• Experiment 13, Behavior of Gases: Molar Mass of a Vapor, p. 137
• Experiment 14, Determination of R: The Gas-Law Constant, p. 149

Resources:

• Instructor's Resource Manual, pp. 116–128
• Student's Guide, pp. 206–227
• Test Bank, pp. 383–423
• Instructor's Resource CD, Chapter 10

Pacing Guide:

• Characteristics of Gases and Pressure—1 day
• General Gas Law from Boyle's Law, Charles's Law, and Gay-Lussac's Law—1 day
• Avogadro's Hypothesis and Ideal Gas Equation—1 day
• Dalton's Law of Partial Pressure and Gas Stoichiometry—1 day
• The Kinetic Molecular Theory and Graham's Law—1 day
• Real Gases
• Block Scheduling
  Spend very little time on individual gas laws. Develop the General Gas Law and from that the ideal gas equation using Avogadro's Hypothesis and the Ideal Gas Equation. Dalton's Law of Partial Pressure and Gas Stoichiometry, and The Kinetic Molecular Theory and Graham's Law will require a block of time. Point out only that there is a real gas equation and what the fudge factors do.

Key Words:

Suggested Exercises:
Critical thinking questions and end-of-chapter activities are included in these exercises.

• pp. 398–405, # 1, 5, 9, 11, 13, 15, 19, 21, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 63, 65, 67, 69, 71, 73, 77, 86, 92, 98, 105.
• eMedia Exercise: p. 405, # 109, 111.

Troubleshooting Tips/Error Traps:

• Each gas in a mixture of gases occupies the same volume, the volume of the container.
• Have students learn the combined gas law rather than spend time on each gas law.
• It's better for students to learn one expression of R (0.0821 L•atm/n•K) using volume in liters and pressure in atm.
• In using Graham's law emphasize that r is rate, not time. Rate is the reciprocal of time.
• Don't spend a lot of time on real gases, except to understand the corrections for volume of, and the attraction between, gas molecules.