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Copyright 2010 Pearson Prentice Hall, Inc.
John E. McMurry Robert C. Fay
Lecture NotesAlan D. EarhartSoutheast Community College Lincoln, NE
General Chemistry: Atoms First
Chapter 9Gases: Their Properties and Behavior
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Chapter 9/2
Gases and Gas Pressure
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 9/5
Gases and Gas Pressure
(exact)
Conversions
1 torr = 1 mm Hg
1 atm = 101 325 Pa
(exact)1 atm = 760 mm Hg
(exact)1 bar = 1 x 10 5 Pa
Pressure :Unit area
Force
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 9/7
The Gas Laws
Ideal Gas : A gas whose behavior follows the gaslaws 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 9/8
The Gas Laws
Boyles Law
V P 1
(constant n and T)
PV = k
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 9/9
The Gas Laws
Boyles Law
P initial V initial = P final V final
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Chapter 9/10
The Gas Laws
Charles Law
V T
(constant n and P)
= k T
V
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 9/11
The Gas Laws
Charles Law
=T final
V finalT initial
V initial
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Chapter 9/12
The Gas Laws
Avogadros Law
(constant T and P)
= k nV
=n
final
V finaln
initial
V initial
V n
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 9/13
The Gas Laws
=Avogadros Law:
P initial V initial = P final V finalBoyles Law:
n finalV final
n initialV initial
Charles Law: =T final
V finalT initial
V initial
Summary
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Chapter 9/14
The Ideal Gas Law
Is there a mathematical relationship between
P , V , n, and T for an ideal gas?
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 9/15
The Ideal Gas Law
Avogadros Law:
PV = nRT = k Boyles Law:
Charles Law:
= k P
RT
n
V =
= k
P
nR
T
V = (n and T are constant)
(n and T are constant)
(n and T are constant)
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 9/16
The Ideal Gas Law
Standard Temperature andPressure (STP) for Gases
Ideal Gas Law: PV = nR T
P = 1 atm
T = 0 C ( 273.15 K )
R is the gas constant and is the same for all gases.
R = 0.082058 K molL atm
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 9/17
The Ideal Gas Law
= 22.414 LV =P
nRT =
What is the volume of 1 mol of gas at STP?
(1 atm)
(1 mol) 0.082058 K molL atm
(273.15 K)
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 9/19
Stoichiometric Relationshipswith Gases
2Na( s ) + 3N 2(g )2NaN 3(s )
The reaction used in the deployment of automobileairbags is the high-temperature decomposition of sodiumazide, NaN 3, to produce N 2 gas. How many liters of N 2 at1.15 atm and 30.0 C are produced by decomposition of
45.0 g NaN 3?
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 9/20
Stoichiometric Relationshipswith Gases
2Na( s ) + 3N 2(g )2NaN 3(s )
45.0 g NaN 3
65.0 g NaN 3
1 mol NaN 3
2 mol NaN 3
3 mol N 2x x
Volume of N 2 produced:
= 1.04 mol N 2
Moles of N 2 produced:
= 22.5 LV =P
nRT =
(1.15 atm)
(1.04 mol) 0.082058K molL atm (303.2 K)
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 9/21
Partial Pressure and DaltonsLaw
P total = P 1 + P 2 + + P N
Mole Fraction ( X
) =
Daltons Law of Partial Pressures : The totalpressure exerted by a mixture of gases in acontainer at constant V and T is equal to the sumof the pressures of each individual gas in the
container.
X i = P total
P i X i = n total
n i or
Total moles in mixture
Moles of component
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 9/24
The Kinetic-Molecular Theoryof Gases
averagespeed
molar mass
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Chapter 9/25
The Kinetic-Molecular Theoryof Gases
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Grahams Law: Diffusion andEffusion of Gases
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 9/27
Grahams Law: Diffusion andEffusion of Gases
Grahams Law : Rate 1m
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The Behavior of Real Gases
The volume of a real gas is larger than predicted by the ideal gas law.
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 9/29
The Behavior of Real Gases
Attractive forces between particles becomemore important at higher pressures.
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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 9/30
The Behavior of Real Gases
P V 2n2
= nRT + V - n
van der Waals equation
ba
Correction for intermolecular
attractions.
Correction for
molecular volume.
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Chapter 9/31
The Earths Atmosphere
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Chapter 9/32
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The Earths Atmosphere