Transcript Chemistry: Atoms First, McMurry and Fay, 1st Edition

John E. McMurry • 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
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
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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
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Chapter 9/7
The Gas Laws
Boyle’s Law
1
V
(constant n and T)
P
PV = k
Chapter 9/8
The Gas Laws
Boyle’s Law
PinitialVinitial = PfinalVfinal
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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
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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:
PinitialVinitial = PfinalVfinal
Vinitial
Tinitial
Vinitial
ninitial
=
=
Vfinal
Tfinal
Vfinal
nfinal
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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 = nRT = k
V
T
V
n
=
=
nR
P
RT
P
(n and T are constant)
=k
(n and T are constant)
=k
(n and T are constant)
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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
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Chapter 9/16
The Ideal Gas Law
What is the volume of 1 mol of gas at STP?
V=
nRT
P
L atm
(1 mol) 0.082058
(273.15 K)
K mol
=
(1 atm)
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= 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)
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Chapter 9/19
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
(303.2 K)
K mol
=
(1.15 atm)
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= 22.5 L
Chapter 9/20
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 =
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Pi
Ptotal
Chapter 9/21
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.
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Chapter 9/22
The Kinetic-Molecular Theory
of Gases
molar
mass
average
speed
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Chapter 9/24
The Kinetic-Molecular Theory
of Gases
Chapter 9/25
Graham’s Law: Diffusion and
Effusion of Gases
Graham’s Law: Diffusion and
Effusion of Gases
Graham’s Law: Rate 
1
m
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Chapter 9/27
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.
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Chapter 9/29
The Behavior of Real Gases
van der Waals equation
Correction for
intermolecular
attractions.
P+
an2
V2
V - n b = nRT
Correction for
molecular
volume.
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Chapter 9/30
The Earth’s Atmosphere
Chapter 9/31
Chapter 9/32
The Earth’s Atmosphere