Chapter 9: Gases: Their Properties and Behavior 4/22/2019 Chapter 9 Gases Copyright © 2008 Pearson Prentice Hall, Inc.

Gases and Gas Pressure Gas mixtures are homogeneous and compressible Chemistry: McMurry and Fay, 6th Edition Chapter 9: Gases: Their Properties and Behavior 4/22/2019 3:30:46 PM Gases and Gas Pressure Gas mixtures are homogeneous and compressible Gas molecules do not interact with each other Copyright © 2011 Pearson Prentice Hall, Inc.

Atmospheric Pressure Atmospheric pressure is the pressure exerted by a column of air from the top of the atmosphere to the surface of the Earth.

Pressure Imbalance in Ear If there is a difference in pressure across the eardrum membrane, the membrane will be pushed out – what we commonly call a “popped eardrum.” picture from Tro Intro Chem 2nd ed.

Gases and Gas Pressure A barometer Chemistry: McMurry and Fay, 6th Edition Chapter 9: Gases: Their Properties and Behavior 4/22/2019 3:30:46 PM Gases and Gas Pressure A barometer measures the pressure exerted by the gases in the atmosphere. indicates atmospheric pressure as the height in mm of the mercury column. Copyright © 2011 Pearson Prentice Hall, Inc.

Gas Pressure Gas pressure is a force acting on a specific area. Pressure (P) = force area has units of atm, mmHg, torr, lb/in.2, and kilopascals(kPa). 1 atm = 760 mm Hg (exact) 1 atm = 760 torr 1 atm = 14.7 lb/in.2 1 atm = 101 325 Pa 1 atm = 101.325 kPa

Gases and Gas Pressure Monometer Pgas > Patm Pgas < Patm Chemistry: McMurry and Fay, 6th Edition Chapter 9: Gases: Their Properties and Behavior 4/22/2019 3:30:46 PM Gases and Gas Pressure Monometer Pgas < Patm Pgas = Patm - PHg Pgas > Patm Pgas = Patm + PHg Copyright © 2011 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 4/22/2019 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 (calculation must be in Kelvin) V volume n number of moles Copyright © 2008 Pearson Prentice Hall, Inc.

The Gas Laws 1 V a (constant n and T) P Chemistry: McMurry and Fay, 6th Edition Chapter 9: Gases: Their Properties and Behavior 4/22/2019 3:30:46 PM The Gas Laws Boyle’s Law a V P 1 (constant n and T) PinitialVinitial = PfinalVfinal One goes up, the other one goes down. Copyright © 2011 Pearson Prentice Hall, Inc.

The Gas Laws Boyle’s Law 1 V a (constant n and T) P Chemistry: McMurry and Fay, 6th Edition Chapter 9: Gases: Their Properties and Behavior 4/22/2019 3:30:46 PM The Gas Laws Boyle’s Law a V P 1 (constant n and T) One goes up, the other one goes down. Copyright © 2011 Pearson Prentice Hall, Inc.

PV Constant in Boyle’s Law In Boyle’s law, the product P x V is constant as long as T and n do not change. P1V1 = 8.0 atm x 2.0 L = 16 atm L P2V2 = 4.0 atm x 4.0 L = 16 atm L P3V3 = 2.0 atm x 8.0 L = 16 atm L Boyle’s law can be stated as P1V1 = P2V2 (T, n constant)

Boyle’s Law and Diving since water is denser than air, for each 10 m you dive below the surface, the pressure on your lungs increases 1 atm at 20 m the total pressure is 3 atm if your tank contained air at 1 atm pressure you would not be able to inhale it into your lungs

Boyles’ Law and Breathing During an inhalation, the lungs expand. the pressure in the lungs decreases. air flows towards the lower pressure in the lungs.

Boyles’ Law and Breathing During an exhalation, lung volume decreases. pressure within the lungs increases. air flows from the higher pressure in the lungs to the outside.

Chapter 9: Gases: Their Properties and Behavior 4/22/2019 The Gas Laws V a T Constant n and P In Charles’s Law, the Kelvin temperature of a gas is directly related to the volume. P and n are constant. when the temperature of a gas increases, its volume increases. One goes up, the other one goes up. Copyright © 2008 Pearson Prentice Hall, Inc.

The Gas Laws = Tfinal Vfinal Tinitial Vinitial Charles’s Law Chemistry: McMurry and Fay, 6th Edition Chapter 9: Gases: Their Properties and Behavior 4/22/2019 3:30:46 PM The Gas Laws Charles’s Law = Tfinal Vfinal Tinitial Vinitial V a T (constant n and P) Copyright © 2011 Pearson Prentice Hall, Inc.

Chapter 9: Gases: Their Properties and Behavior 4/22/2019 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.

Chapter 9: Gases: Their Properties and Behavior The Ideal Gas Law 4/22/2019 Summary Boyle’s Law: PinitialVinitial = PfinalVfinal = Tfinal Vfinal Tinitial Vinitial Charles’ Law: ninitial Vinitial nfinal Vfinal Avogadro’s 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. Copyright © 2008 Pearson Prentice Hall, Inc.

Examples If a sample of helium gas has a volume of 120 mL and a pressure of 850 mmHg, what is the new volume if the pressure is changed to 425 mmHg? A sample of oxygen gas has a volume of 420 mL at a temperature of 18 °C. At what temperature (in °C) will the volume of the oxygen be 640 mL (P and n constant)? If 0.75 mole of helium gas occupies a volume of 1.5 L, what volume will 1.2 moles of helium occupy at the same temperature and pressure?

Combine Gas Law is an expression obtained by mathematically combining Boyle’s and Charles’ law P1V1 = P2V2 @ constant n T1 T2 can predict P, V or T when condition is changed

Examples A gas has a volume of 675 mL at 35 °C and 0.850 atm pressure. What is the volume (mL) of the gas at -95 °C and a pressure of 802 mmHg? (n constant)

Chapter 9: Gases: Their Properties and Behavior 4/22/2019 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.

Examples What volume is occupied by 25.7 g of carbon dioxide gas at 25.0oC and 371 torr? Determine the molar mass of a gas with a density of 1.905 g/L at 80.0oC

The Ideal Gas Law What is the volume of 1 mol of gas at STP? (1 atm) Chemistry: McMurry and Fay, 6th Edition Chapter 9: Gases: Their Properties and Behavior The Ideal Gas Law 4/22/2019 3:30:46 PM What is the volume of 1 mol of gas at STP? (1 atm) (1 mol) 0.08206 K mol L atm (273.15 K) P nRT V = = = 22.41 L The closer the molar volume of a gas is to 22.41 L at STP, the more ideal the behavior. Copyright © 2011 Pearson Prentice Hall, Inc.

Molar Volume At standard temperature and pressure (STP), 1 mole of a gas occupies a volume of 22.4 L, which is called its molar volume.

Example A. What is the volume at STP of 4.00 g of CH4? 1) 5.60 L 2) 11.2 L 3) 44.8 L B. How many g of He are present in 8.00 L of gas at STP? 1) 25.6 g 2) 0.357 g 3) 1.43 g