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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


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