Transcript Chemistry: McMurry and Fay, 5th Edition

John E. McMurry • Robert C. Fay
C H E M I S T R Y
Fifth Edition
Chapter 9
Gases: Their Properties and Behavior
Lecture Notes
Alan D. Earhart
Southeast Community College • Lincoln, NE
Copyright © 2008 Pearson Prentice Hall, Inc.
Gases and Gas Pressure
Gas mixtures are homogeneous and compressible.
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/2
Gases and Gas Pressure
Force
Pressure:
Unit area
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/3
Gases and Gas Pressure
Barometer
Force
Pressure:
Unit area
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/4
Gases and Gas Pressure
Units
Barometer
Pa
torr
mm Hg
atm
bar
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/5
Gases and Gas Pressure
Units
Pa
torr
mm Hg
atm
bar
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
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/6
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.
Chapter 9/8
The Gas Laws
Boyle’s Law
1
Va
(constant n and T)
P
PV = k
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/9
The Gas Laws
Boyle’s Law
1
Va
(constant n and T)
P
PV = k
PinitialVinitial = PfinalVfinal
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/10
The Gas Laws
Charles’ Law
Va T
(constant n and P)
V
T
Copyright © 2008 Pearson Prentice Hall, Inc.
=k
Chapter 9/11
The Gas Laws
Charles’ Law
Va T
(constant n and P)
V
T
Vinitial
Tinitial
Copyright © 2008 Pearson Prentice Hall, Inc.
=k
=
Vfinal
Tfinal
Chapter 9/12
The Gas Laws
Avogadro’s Law
Va n
(constant T and P)
V
n
Vinitial
ninitial
Copyright © 2008 Pearson Prentice Hall, Inc.
=k
=
Vfinal
nfinal
Chapter 9/13
The Ideal Gas Law
Summary
Boyle’s Law:
Charles’ Law:
Avogadro’s Law:
PinitialVinitial = PfinalVfinal
Vinitial
Tinitial
Vinitial
ninitial
=
=
Vfinal
Tfinal
Vfinal
nfinal
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/14
The Ideal Gas Law
Is there a mathematical relationship between
P, V, n, and T for an ideal gas?
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/15
The Ideal Gas Law
Ideal Gas Law:
PV = nRT
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
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/16
The Ideal Gas Law
What is the volume of 1 mol of gas at STP?
(1 mol) 0.082058
V=
nRT
P
=
L atm
K mol
(273.15 K)
(1 atm)
Copyright © 2008 Pearson Prentice Hall, Inc.
= 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, 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?
2NaN3(s)
2Na(s) + 3N2(g)
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/18
Stoichiometric Relationships
with Gases
2NaN3(s)
2Na(s) + 3N2(g)
Moles of N2 produced:
45.0 g NaN3
x
1 mol NaN3
65.0 g NaN3
x
3 mol N2
2 mol NaN3
= 1.04 mol N2
Volume of N2 produced:
V=
nRT
P
L atm
(1.04 mol) 0.082058
(303.15 K)
K mol
=
(1.15 atm)
Copyright © 2008 Pearson Prentice Hall, Inc.
= 22.5 L
Chapter 9/19
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
Mole Fraction (X) =
Moles of component
Total moles in mixture
Xi =
ni
ntotal
or
Xi =
Copyright © 2008 Pearson Prentice Hall, Inc.
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.
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/21
The Kinetic-Molecular Theory
of Gases
molar
mass
average
speed
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/23
The Kinetic-Molecular Theory
of Gases
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/24
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.
Chapter 9/25
Graham’s Law: Diffusion and
Effusion of Gases
Effusion: The escape of a gas through a pinhole
into a vacuum without molecular collisions.
Graham’s Law:
Copyright © 2008 Pearson Prentice Hall, Inc.
Rate a
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.
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/27
The Behavior of Real Gases
Attractive forces between particles become
more important at higher pressures.
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/28
The Behavior of Real Gases
van der Waals equation
Correction for
intermolecular
attractions.
an2
P+ 2
V
V - n b = nRT
Correction for
molecular
volume.
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/29
The Earth’s Atmosphere
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/30
The Earth’s Atmosphere