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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

(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

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

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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