ISM_chapter10_part1

ISM_chapter10_part1 - Chapter 10 Gases and the Atmosphere...

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Chapter 10: Gases and the Atmosphere 449 Chapter 10: Gases and the Atmosphere Teaching for Conceptual Understanding Several named laws (Avogadro’s, Boyles, Charles’s, and Dalton’s partial pressures) describe the basis properties of gases. Remember it is the relationships among pressure, volume, temperature, and amount of gas that are important and not the name of the person who discovered the relationship. Students will grasp and retain the gas laws more readily if the laws are presented on a macroscopic, particulate, mathematical and graphical level. The particulate nature of gases can be easily illustrated with a Molecular Motion Demonstrator (Educational Materials and Equipment Company) that fits on an overhead projector. Movement of ball bearings in a glass frame at varying levels of vibration is used to show random motion of gas molecules, Avogadro’s law, Boyles’s law, Charles’s law and diffusion. Two misconceptions students have about gases are (1) as a gas is compressed, the volume decreases, pressure increases, and mass decreases, and (2) gases have no mass. Weighing a balloon empty and then inflated will show that gases do indeed have mass. Another misconception is that no matter exists at absolute zero. Figure 10.11 shows the volume of gas is zero at absolute zero. Explain that real atoms or molecules originally in the gas state are now condensed. Every day during weather reports, students hear the barometric pressure reading but few understand what it is. Demonstrating a simple barometer as shown in Figure 10.4, or setting up a barometer in your classroom for daily monitoring will help students visualize the effect of atmospheric pressure. Students tend to believe that colorless gases are safe, and that colored gases are pollution. Point out that the many colorless gases are dangerous. Suggestions for Effective Learning Boyle’s law can be demonstrated by placing an inflated balloon under a bell jar and drawing a vacuum on it. Charles’s law can be demonstrated by adding a cup of boiling water to a gallon-size metal can (empty, clean, paint thinner cans work well) and then screwing on the cap. The stoichiometry of gases provides an excellent review of general stoichiometry concepts. Use this time to revisit mole-to-mole, mole-to-gram, gram-to-mole, gram-to-gram, solution stoichiometry, and limiting reactants. Be sure to discuss automobile air bags with your class because it is one of the few real-world application of gas law stoichiometry. Although gas law calculations are generally algorithmic, students are unsuccessful because of simple errors. Tell them to be on the look out for these: (1) density of gases is in units of g/L and not g/mL, (2) not converting temperature in °C to K, and (3) using the wrong ideal gas law constant.
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ISM_chapter10_part1 - Chapter 10 Gases and the Atmosphere...

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