Chapter 9: Gases: Their Properties and Behavior 5/1/2019 Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 5/1/2019 Gases and Gas Pressure Gas mixtures are homogeneous and compressible. Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 5/1/2019 Gases and Gas Pressure Unit area Force Pressure: Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 5/1/2019 Gases and Gas Pressure Barometer Unit area Force Pressure: Mercury is used in barometers because of its density: 13.6 g/mL. A corresponding water barometer would be 3 stories high! The Journal of Chemical Education published an article about constructing one- de Grys, Hans; Thirty Feet and Rising: Constructing and Using a Water Barometer To Explore Chemical Principles; J. Chem. Educ. 2003, 80, 1156. Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 5/1/2019 Gases and Gas Pressure Units Barometer Pa torr mm Hg atm bar Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 5/1/2019 Gases and Gas Pressure Units Conversions Pa torr mm Hg atm bar 1 atm = 760 mm Hg (exact) 1 torr = 1 mm Hg (exact) 1 bar = 1 x 105 Pa (exact) 1 atm = 101 325 Pa Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 5/1/2019 Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 5/1/2019 The Gas Laws Ideal Gas: A gas whose behavior follows the gas laws exactly. The physical properties of a gas can be defined by four variables: P pressure T temperature V volume n number of moles Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 5/1/2019 The Gas Laws Boyle’s Law a V P 1 (constant n and T) PV = k Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 5/1/2019 The Gas Laws Boyle’s Law a V P 1 (constant n and T) PV = k PinitialVinitial = PfinalVfinal One goes up, the other one goes down. Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 5/1/2019 The Gas Laws Charles’ Law V a T (constant n and P) = k T V Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 5/1/2019 The Gas Laws Charles’ Law V a T (constant n and P) = k T V = Tfinal Vfinal Tinitial Vinitial One goes up, the other one goes up. Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 5/1/2019 The Gas Laws Avogadro’s Law V a n (constant T and P) = k n V = nfinal Vfinal ninitial Vinitial One goes up, the other one goes up. Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 5/1/2019 The Ideal Gas Law Summary Boyle’s Law: PinitialVinitial = PfinalVfinal = Tfinal Vfinal Tinitial Vinitial Charles’ Law: It is not necessary to know the names of the gas laws in order to solve problems. If one remembers the relationships between pressure, volume, temperature, and moles, then one can determine how to work the problem. ninitial Vinitial nfinal Vfinal Avogadro’s Law: = Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 5/1/2019 The Ideal Gas Law These values are all around 22 L for 1 mol of gas. Is there a mathematical relationship between P, V, n, and T for an ideal gas? Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 5/1/2019 The Ideal Gas Law Ideal Gas Law: PV = nRT R is the gas constant and is the same for all gases. R = 0.082058 K mol L atm T = 0 °C (273.15 K) Standard Temperature and Pressure (STP) for Gases Standard pressure is actually 1 bar. Gas law problems must use Kelvin!!!!!! P = 1 atm Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 5/1/2019 The Ideal Gas Law What is the volume of 1 mol of gas at STP? The closer the molar volume of a gas is to 22.414 L at STP, the more ideal the behavior. (1 atm) (1 mol) 0.082058 K mol L atm (273.15 K) P nRT V = = = 22.414 L Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Stoichiometric Relationships with Gases Chapter 9: Gases: Their Properties and Behavior 5/1/2019 Stoichiometric Relationships with Gases The reaction used in the deployment of automobile airbags is the high-temperature decomposition of sodium azide, NaN3, to produce N2 gas. How many liters of N2 at 1.15 atm and 30.0 °C are produced by decomposition of 45.0 g NaN3? 2Na(s) + 3N2(g) 2NaN3(s) Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Stoichiometric Relationships with Gases Chapter 9: Gases: Their Properties and Behavior 5/1/2019 Stoichiometric Relationships with Gases 2Na(s) + 3N2(g) 2NaN3(s) Moles of N2 produced: 45.0 g NaN3 65.0 g NaN3 1 mol NaN3 2 mol NaN3 3 mol N2 x x = 1.04 mol N2 Volume of N2 produced: (1.15 atm) (1.04 mol) 0.082058 K mol L atm (303.15 K) P nRT V = = = 22.5 L Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Partial Pressure and Dalton’s Law Chapter 9: Gases: Their Properties and Behavior 5/1/2019 Partial Pressure and Dalton’s Law Dalton’s Law of Partial Pressures: The total pressure exerted by a mixture of gases in a container at constant V and T is equal to the sum of the pressures of each individual gas in the container. Ptotal = P1 + P2 + … + PN Total moles in mixture Moles of component I’ve just presented the result for mole fraction in terms of component and total pressures without showing the derivation. Mole Fraction (X) = Xi = ntotal ni Xi = Ptotal Pi or Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

The Kinetic-Molecular Theory of Gases Chapter 9: Gases: Their Properties and Behavior 5/1/2019 The Kinetic-Molecular Theory of Gases A gas consists of tiny particles, either atoms or molecules, moving about at random. The volume of the particles themselves is negligible compared with the total volume of the gas; most of the volume of a gas is empty space. The gas particles act independently of one another; there are no attractive or repulsive forces between particles. Collisions of the gas particles, either with other particles or with the walls of a container, are elastic (constant temperature). The average kinetic energy of the gas particles is proportional to the Kelvin temperature of the sample. Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 5/1/2019 Copyright © 2008 Pearson Prentice Hall, Inc.

The Kinetic-Molecular Theory of Gases Chapter 9: Gases: Their Properties and Behavior 5/1/2019 The Kinetic-Molecular Theory of Gases molar mass average speed Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

The Kinetic-Molecular Theory of Gases Chapter 9: Gases: Their Properties and Behavior 5/1/2019 The Kinetic-Molecular Theory of Gases Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Graham’s Law: Diffusion and Effusion of Gases Chapter 9: Gases: Their Properties and Behavior 5/1/2019 Graham’s Law: Diffusion and Effusion of Gases Diffusion: The mixing of different gases by molecular motion with frequent molecular collisions. Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

Graham’s Law: Diffusion and Effusion of Gases Chapter 9: Gases: Their Properties and Behavior 5/1/2019 Graham’s Law: Diffusion and Effusion of Gases Effusion: The escape of a gas through a pinhole into a vacuum without molecular collisions. a Rate 1 m Graham’s Law: m is mass. Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

The Behavior of Real Gases Chapter 9: Gases: Their Properties and Behavior 5/1/2019 The Behavior of Real Gases The volume of a real gas is larger than predicted by the ideal gas law. Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

The Behavior of Real Gases Chapter 9: Gases: Their Properties and Behavior 5/1/2019 The Behavior of Real Gases Attractive forces between particles become more important at higher pressures. Particles are closer together at higher pressures due to the increased attractive forces. Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

The Behavior of Real Gases Chapter 9: Gases: Their Properties and Behavior 5/1/2019 The Behavior of Real Gases van der Waals equation Correction for intermolecular attractions. a n2 P + V - n b = nRT V2 Correction for molecular volume. Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

The Earth’s Atmosphere Chapter 9: Gases: Their Properties and Behavior 5/1/2019 The Earth’s Atmosphere Copyright © 2008 Pearson Prentice Hall, Inc. Copyright © 2008 Pearson Prentice Hall, Inc.

The Earth’s Atmosphere Chapter 9: Gases: Their Properties and Behavior 5/1/2019 The Earth’s Atmosphere Copyright © 2008 Pearson Prentice Hall, Inc.