John E Mc Murry Robert C Fay General
John E. Mc. Murry • Robert C. Fay General Chemistry: Atoms First Chapter 9 Gases: Their Properties and Behavior Lecture Notes Alan D. Earhart Southeast Community College • Lincoln, NE Copyright © 2010 Pearson Prentice Hall, Inc.
Gases and Gas Pressure Chapter 9/2
Gases and Gas Pressure: Force Unit area Conversions 1 atm = 760 mm Hg (exact) 1 torr = 1 mm Hg (exact) 1 bar = 1 x 105 Pa (exact) 1 atm = 101 325 Pa Chapter 9/5
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 Chapter 9/7
The Gas Laws Boyle’s Law 1 V P (constant n and T) PV = k Chapter 9/8
The Gas Laws Boyle’s Law Pinitial. Vinitial = Pfinal. Vfinal Chapter 9/9
The Gas Laws Charles’ Law V T (constant n and P) V T =k Chapter 9/10
The Gas Laws Charles’ Law Vinitial Tinitial = Vfinal Tfinal Chapter 9/11
The Gas Laws Avogadro’s Law V n (constant T and P) V n Vinitial ninitial =k = Vfinal nfinal Chapter 9/12
The Gas Laws Summary Boyle’s Law: Charles’ Law: Avogadro’s Law: Pinitial. Vinitial = Pfinal. Vfinal Vinitial Tinitial Vinitial ninitial = = Vfinal Tfinal Vfinal nfinal Chapter 9/13
The Ideal Gas Law Is there a mathematical relationship between P, V, n, and T for an ideal gas? Chapter 9/14
The Ideal Gas Law Boyle’s Law: Charles’ Law: Avogadro’s Law: PV = n. RT = k V T V n = = n. R P RT P (n and T are constant) =k (n and T are constant) Chapter 9/15
The Ideal Gas Law: PV = n. RT R is the gas constant and is the same for all gases. L atm R = 0. 082058 K mol Standard Temperature and Pressure (STP) for Gases T = 0 °C (273. 15 K) P = 1 atm Chapter 9/16
The Ideal Gas Law What is the volume of 1 mol of gas at STP? (1 mol) 0. 082058 V= n. RT P = L atm K mol (1 atm) (273. 15 K) = 22. 414 L Chapter 9/17
Stoichiometric Relationships with Gases The reaction used in the deployment of automobile airbags is the high-temperature decomposition of sodium azide, Na. N 3, to produce N 2 gas. How many liters of N 2 at 1. 15 atm and 30. 0 °C are produced by decomposition of 45. 0 g Na. N 3? 2 Na. N 3(s) 2 Na(s) + 3 N 2(g) Chapter 9/18
Stoichiometric Relationships with Gases 2 Na. N 3(s) 2 Na(s) + 3 N 2(g) Moles of N 2 produced: 45. 0 g Na. N 3 x 1 mol Na. N 3 65. 0 g Na. N 3 x 3 mol N 2 2 mol Na. N 3 = 1. 04 mol N 2 Volume of N 2 produced: V= n. RT P L atm (1. 04 mol) 0. 082058 (303. 2 K) K mol = (1. 15 atm) = 22. 5 L Chapter 9/19
Partial Pressure and 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 = P 1 + P 2 + … + PN Mole Fraction (X) = Moles of component Total moles in mixture Xi = ni ntotal or Xi = Pi Ptotal Chapter 9/20
The Kinetic-Molecular Theory of Gases 1. A gas consists of tiny particles, either atoms or molecules, moving about at random. 2. 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. 3. The gas particles act independently of one another; there are no attractive or repulsive forces between particles. 4. Collisions of the gas particles, either with other particles or with the walls of a container, are elastic (constant temperature). 5. The average kinetic energy of the gas particles is proportional to the Kelvin temperature of the sample. Chapter 9/21
The Kinetic-Molecular Theory of Gases molar mass average speed Chapter 9/23
The Kinetic-Molecular Theory of Gases Chapter 9/24
Graham’s Law: Diffusion and Effusion of Gases
Graham’s Law: Diffusion and Effusion of Gases Graham’s Law: Rate 1 m Chapter 9/26
The Behavior of Real Gases The volume of a real gas is larger than predicted by the ideal gas law.
The Behavior of Real Gases Attractive forces between particles become more important at higher pressures. Chapter 9/28
The Behavior of Real Gases van der Waals equation Correction for intermolecular attractions. a n 2 P+ 2 V V - n b = n. RT Correction for molecular volume. Chapter 9/29
The Earth’s Atmosphere Chapter 9/30
Chapter 9/31
The Earth’s Atmosphere
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