University:
Arizona State University
Course:
CHM 101 | Introductory Chemistry
Academic year:

2021
Views:

102

Pages:

43
Author:

Hen Par

Chapter 9: The Gaseous State 9-1 Questions for Consideration 1. 2. 3. 4. What are some general properties of gases? How does the behavior of gases vary with changes in pressure, temperature, volume and number of molecules (atoms)? What are the mathematical relationships between volume, pressure, temperature, and amount of gas? What is the theory that explains the behavior of gases in terms of atomic or molecular motion? 9-2 Chapter 9 Topics: 1. 2. 3. 4. The Behavior of Gases Factors That Affect the Properties of Gases The Ideal Gas Law Kinetic-Molecular Theory of Gases Use the notes, recitation activity, and lab as a guide. Skip section 9.5. 9-3 Gases in Our Atmosphere Although we don’t see them, we are surrounded by mixtures of various gases in our atmosphere. TABLE 9.1 Volume Percent of Gases in the Atmosphere Gas Volume Percent Gas Volume Percent Gas Volume Percent N2 78.09 CH4 0.00015 O3 0.000002 O2 20.94 Kr 0.0001 NH3 0.000001 Ar 0.93 H2 0.00005 NO2 0.0000001 CO2 0.032 N2O 0.000025 SO2 0.00000002 Ne 0.0018 CO 0.00001 H2O Varies He 0.00052 Xe 0.000008 9-4 9.1 The Behavior of Gases   One way that we can describe gases is by their density. All gases have a relatively low densities in comparison to liquids and solids, due to the large amount of empty space between molecules. Figure 1.24 9-5 Density Because of their low densities, gases exist above the Earth and bubble up through liquids. Figure 9.13 9-6 Behavior of Gases at the Molecular Level   Gases consist of particles (atoms or molecules) that are relatively far apart. Gas particles move about rapidly.    An average O2 molecule moves at a velocity of 980 mi/hr at room temperature. Gas particles have little effect on one another unless they collide. When they collide, they do not stick to one another. Gases expand to fill their containers. 9-7 Temperature and Density  All gases expand when heated.   Why? Because the resulting temperature increase causes an increase in the kinetic energy of the gas molecules, making them move faster, collide harder, and spread out. Which gas has the greatest density? Figure 9.3 9-8 Why does a hot air balloon rise in the atmosphere? Figure 9.4 9-9 Pressure    Changes in pressure and amount of gas can affect the properties of a gas. What happens to volume and pressure when air molecules are added to the tire? What happens to density? Figure 9.5 9-10 Pressure What causes the balloon to inflate? Figure 9.7 Figure 9.1 9-11 Pressure  Pressure (P) is the amount of force applied per unit area: force Pressure (P) = area  We can describe the pressure exerted by gas particles by: Figure 9.7 force of gas particles Pressure (P) = area of container 9-12 Pressure Which finger hurts? Figure from p. 348 Figure from p. 348 Figure 9.8 force Pressure (P) = area 9-13 Which gas has the greater pressure? (assume they are at the same temperature) Figure 9.9 9-14 Pressure Why does the can crush when the air is removed from the inside? Figure 9.10 9-15 Measuring Pressure (Units)  psi    pounds per square inch lb/in2 Atmospheric pressure is commonly measured with a barometer.     inches of Hg mmHg torr atm 1 atm = 760 mmHg 1 atm = 760 torr 1 atm = 101,325 Pa Figure 9.11 9-16 9.2 Factors that Affect the Properties of Gases Volume and Pressure   As a weather balloon ascends to higher altitudes of lower pressures, its volume increases. As bubbles rise in water from greater pressures to lower pressures, they increase in size. Figure 9.12 Figure 9.13 9-17 Volume and Pressure How are volume and pressure related? Figure 9.14 For a given amount of gas at the same temperature, the pressure goes up as the volume gets smaller 9-18 Graph of Volume vs. Pressure What does this graph illustrate regarding the relationship between volume and pressure? Figure 9.15 9-19 What happens to pressure when the volume is doubled? Figure from p. 352 9-20 Graph of Volume vs. 1/Pressure shows that they are inversely related. V = (constant) × 1/P (at constant temperature) Figure 9.16 9-21 Boyle’s Law Application  Use Boyle’s Law to explain why potato chip bags are puffier with greater volume at higher altitudes. Figure from p. 354 9-22 Activity: Boyle’s Law P1V1 = P2V2 If the pressure of a 2.0-L sample of gas is decreased from 1.2 atm to 0.25 atm at constant temperature, what is the new volume? 9-23 Volume and Temperature What is the relationship between volume and temperature (at constant pressure)? Figure 9.17 9-24 Charles’s Law VT V/T = constant V = constant × T T = constant × V V vs. T at constant pressure Temperature must be in units of Kelvin. Figure 9.18 9-25 Volume, Pressure, and Temperature Combined gas law • For a constant amount of gas, volume is proportional to absolute temperature and inversely proportional to pressure. V  (T/P) PV So 1 1  constant T1 PV PV 1 1  2 2 T1 T2 9-26 Volume and Moles of Gas   What happens to volume when air molecules are added to the tire? Why does the can crush when the air is removed from the inside? 9-27 Volume vs. Amount of Gas 1 Avogadro’s hypothesis • The volume occupied by a gas at a given temperature and pressure is directly proportional to the number of gas particles and thus to the moles of gas. Vn Figure 9.20 As the moles of gas increase, the volume increases (at constant T and P). 9-28 Gay-Lussac’s Law of Combining Volumes (1808) Gases combine in simple whole-number volume proportions at constant temperature and pressure. Figure 9.19 9-29 9.3 The Ideal Gas Law PV = constant (R) nT PV  nRT 9-30 The Ideal Gas Law PV R= nT (1 atm)(22.414 L) R= (1.000 mol)(273.15 K) L atm R = 0.08206 mol K 9-31 The Ideal Gas Law  The ideal gas law allows us to calculate pressure, volume, moles, or temperature, when three out of the four variables are known.  If the identity of the gas is known, molar mass can be used to convert between moles and grams. 9-32 The Ideal Gas Law What mass of oxygen gas will occupy a 6.0-liter container, at a pressure of 700 torr and at a temperature of 25.0C? PV = nRT 760 torr = 1 atm TK = TC + 273.15 L atm The value of R is 0.08206 mol K 9-33 The Ideal Gas Law What mass of oxygen gas will occupy a 6.0-liter container, at a pressure of 700 torr and at a temperature of 25.0C? 9-34 9.4 Kinetic-Molecular Theory of Gases Postulates of KMT 1. Gases are composed of small and widely separated particles (molecules or atoms). • 2. 3. 4. 5. In a normal gas, less than 0.1% of the space is due to the volume of the gas particles. The rest is empty space. Particles of a gas behave independently of one another. Each particle of a gas is in rapid, straight-line motion, until it collides with another molecule or with its container. The pressure of a gas arises from the sum of the collisions of the particles with the walls of the container. The average kinetic energy of gas particles depends only on the absolute temperature: KEav  TKelvin • This means that all gases have the same average KE when at the same temperature. 9-35 Kinetic Energy, Molecular Velocity, and Temperature For a particular gas, KE is related to molecular velocity: KEave=½m(vave)2 Figure 9.23 9-36 Activity: Gas Properties 1. 2. 3. 4. Which balloon has the greatest number of gas molecules? Which balloon has the greatest number of moles of gas? Which balloon has the greatest mass? Which balloon has the greatest density? Figure from p. 388 9-37 Activity: Gas Properties If the O2 balloon had been filled to a smaller volume, which of the following quantities would be different for the O2 gas?     number of molecules moles mass density 9-38 Dalton’s Law of Partial Pressures Gases in a mixture behave independently and exert the same pressure they would exert if they were in a container alone. Ptotal = PA + PB + PC + … Figure 9.21 9-39 Activity: Kinetic Energy, Molecular Velocity, and Temperature Ar, CO2, and H2 all at the same temperature 1. Which of these gases has the greatest average kinetic energy? 2. Which has the greatest average velocity? 9-40 Diffusion Figure 9.24 Figure 9.25 9-41 Effusion A helium balloon loses volume more quickly than an “air” balloon because helium effuses through the balloon’s pores more quickly. Figure 9.26 9-42 Activity: Diffusion and Effusion Ar, CO2, and H2 all at the same temperature 1. Which of these gases diffuses at the greatest rate? 2. Which of these gases effuses at the greatest rate? 9-43