End Show Slide 1 of 30 Chemistry 14.4

Ideal Gases and Real Gases Under what conditions are real gases most likely to differ from ideal gases? Ideal gases obey the gas laws and behave according to the Kinetic Molecular Theory. No gas is a true ideal gas but He and H 2 behave most like an ideal gas especially when P is low and T is high. There are attractions between the particles in a gas. Because of these attractions, a gas can condense,or even solidify, when it is compressed or cooled.

Real gases differ most from an ideal gas at low temperatures and high pressures. Gases behave most like an ideal gas at high temperatures and low pressures.

End Show © Copyright Pearson Prentice Hall Slide 4 of Gases: Mixtures and Movements A list of gear for an expedition to Mount Everest includes climbing equipment, ski goggles, a down parka with a hood, and most importantly compressed-gas cylinders of oxygen. You will find out why a supply of oxygen is essential at higher altitudes.

© Copyright Pearson Prentice Hall Slide 5 of 30 End Show Dalton’s Law How is the total pressure of a mixture of gases related to the partial pressures of the component gases? Dalton’s law of partial pressures states that, at constant volume and temperature, the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the component gases.

End Show Slide 6 of 30 © Copyright Pearson Prentice Hall Gases: Mixtures and Movements > 14.4 Dalton’s Law The contribution each gas in a mixture makes to the total pressure is called the partial pressure exerted by that gas.

End Show Slide 7 of 30 © Copyright Pearson Prentice Hall Gases: Mixtures and Movements > 14.4 Dalton’s Law Three gases are combined in container T.

End Show Slide 8 of 30 © Copyright Pearson Prentice Hall Gases: Mixtures and Movements > 14.4 Dalton’s Law The partial pressure of oxygen must be kPa or higher to support respiration in humans. The climber below needs an oxygen mask and a cylinder of compressed oxygen to survive.

© Copyright Pearson Prentice Hall SAMPLE PROBLEM Slide 9 of 30 End Show 14.6

© Copyright Pearson Prentice Hall SAMPLE PROBLEM Slide 10 of 30 End Show 14.6

© Copyright Pearson Prentice Hall SAMPLE PROBLEM Slide 11 of 30 End Show 14.6

© Copyright Pearson Prentice Hall Slide 12 of 30 End Show Practice Problems for Sample Problem 14.6 INDEX CARD activity (turn in for evaluation)

© Copyright Pearson Prentice Hall Slide 13 of 30 End Show Graham’s Law How does the molar mass of a gas affect the rate at which the gas effuses or diffuses? Diffusion is the tendency of molecules to move toward areas of lower concentration until the concentration is uniform throughout. During effusion, a gas escapes through a tiny hole in its container.

End Show Slide 14 of 30 © Copyright Pearson Prentice Hall 14.4 Gases: Mixtures and Movements > Graham’s Law Gases of lower molar mass diffuse and effuse faster than gases of higher molar mass. Thomas Graham’s Contribution: Graham’s law of effusion states that the rate of effusion of a gas is inversely proportional to the square root of the gas’s molar mass. This law can also be applied to the diffusion of gases.

End Show Slide 15 of 30 © Copyright Pearson Prentice Hall 14.4 Gases: Mixtures and Movements > Graham’s Law Comparing Effusion Rates A helium filled balloon will deflate sooner than an air-filled balloon. Helium atoms are less massive than oxygen or nitrogen molecules. So the molecules in air move more slowly than helium atoms with the same kinetic energy.

End Show Slide 16 of 30 © Copyright Pearson Prentice Hall 14.4 Gases: Mixtures and Movements > Graham’s Law Thomas Graham’s Contribution Graham’s law of effusion states that the rate of effusion of a gas is inversely proportional to the square root of the gas’s molar mass. This law can also be applied to the diffusion of gases.

End Show Slide 17 of 30 © Copyright Pearson Prentice Hall 14.4 Gases: Mixtures and Movements > Graham’s Law Helium effuses (and diffuses) nearly three times faster than nitrogen at the same temperature. Animations and practice problems for diffusion and effusion

End Show © Copyright Pearson Prentice Hall Slide 18 of 30 Section Quiz -or- Continue to: Launch: Assess students’ understanding of the concepts in Section 14.4 Section Quiz

© Copyright Pearson Prentice Hall Slide 19 of 30 End Show 14.4 Section Quiz. 1. What is the partial pressure of oxygen in a diving tank containing oxygen and helium if the total pressure is 800 kPa and the partial pressure of helium is 600 kPa? a.200 kPa b.0.75 kPa c kPa d.1.33 kPa

© Copyright Pearson Prentice Hall Slide 20 of 30 End Show 14.4 Section Quiz. 2. A mixture of three gases exerts a pressure of 448 kPa, and the gases are present in the mole ratio 1 : 2 : 5. What are the individual gas pressures? a.44 kPa, 88 kPa, and 316 kPa b.52 kPa, 104 kPa, and 292 kPa c.56 kPa, 112 kPa, and 280 kPa d.84 kPa, 168 kPa, and 196 kPa

© Copyright Pearson Prentice Hall Slide 21 of 30 End Show 14.4 Section Quiz. 3. Choose the correct words for the spaces. Graham's Law says that the rate of diffusion of a gas is __________ proportional to the square root of its _________ mass. a.directly, atomic b.inversely, atomic c.inversely, molar d.directly, molar