Preview principles of physical chemistry by dr mahbubul haque, dr mohammad yousuf ali mollah

Huque and Nawab

Principles of
Physical Chemistry

Fully Revised by
Dr. Muhammad Mahbubul Huque
Dr. Muhammad Yousuf All Mollah
/ Ị P Brothers' Publications


■' r

.

Huque and Nawab

Principles of Physical
Chemistry

I

Revised by

__ jumad Mahbubul Huque
Mohammad Yousuf A. Mollah

Brothers' Publication
3 / 5 , Rafme Plaza
Mirpur Road, D haka-1205

January, 2009


P u b lish e d by
B ro th ers' Publication
3/5, Rafine Pia2a
M irpur Road, D haka-1205

First Edition : 1968
Second Edition : 1971
Fully Revised Edition : 2009 \

Fully Revised Edition-20\

(All rights reserved, no part of this publication can be reproduced in any farm
w ithout the prior perm ission o f the authors.]

C o m p o sed by
Alka Com puter
Banglabazar, D h ak a-1100


Muhammad Mahbubul Hu que
M.Sc. (Dhaka), Ph. D. (McGill, Canada)
Former Professor
Department o f Chemistry
Dhaka University, Dhaka
and
,
■

Founding Chairman
Department o f Chemistry
Jahangimagai University
Savar, Dhaka

Mohammad Yousuf All Moliah
M.Sc. (Dhaka), Ph. D. (Macquarie, Australia)
Professor
Department o f Chemistry
Dhaka University, Dhaka

cr"


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Dedicated to the memory of

Late Professor M. Ali Nawab
Professor M. A. Nawab was (he senior author o f the First Edition o f
the book. He was Professor of the Department o f Chemistry o f Dhaka
University. Late Professor Nciiuab xoas the Chairman o f the
Department o f Chemistry of Dhaka University during 1973-Ĩ976.
Professor Nawab expired on 23 April 1993.

PREFACE TO THE REVISED EDITION
The first edition of 'Principles o f Physical C hem istry' was published in 196S and the third edition cam e in
1974. The authors did not make attem pts to bring out further editions of the book as at th.ii time science
texl books written in Bengali were preferred by the students. W e had forgotten aboui ihe book. Professor
M. A. Nawab, [he senior author expired in 1993. Then about three years back a former student o f mine who
was doing undergraduate studies in Pharmacy in a Private University in Dhaka showed me a photocopy of
ihe original third edition o f the book which was being used as a text book. This was described as a ‘fully
revised edition’, A survey revealed that a large num ber o f students in different universities and colleges in
Banzladesh were using this Tully revised edition’ as a text book o f Physical Chemistry. As mentioned this
was not a Revised Edition as the authors did not m ake any revision after Ihe third edition. Professor M.
Y ousuf A. M ollah. Professor o f Physical Chem istry at the Dhaka U niversity, persuaded me to prepare a
revised edition. I agreed on condition that he will be a co-author. The book on Physical Chem istry being
presented with !he same title as !he original one is (he result o f joint efforts o f Prof. M. Y ousuf A. Mollah
and me. We traced the printing house which had been marketing ibe photocopies as 'fully revised edition’.
They apologized for their action and agreed to publish the edition we have prepared.
This is a Fully Revised Edition with m ajor changes. W hite rewriting this book we focused on !he syllabii of
undergraduate courses o r Physical C hem istry o f Public, Private U niversities and U niversity Colieges in
Bangladesh. The students o f Pharm acy, Biochemistry and Engineering will also be benefited from this
book. All through the book SI units have been used. Many chapters have been rewritten with additional
materials. A num ber o f chapters have been divided into sm aller chapters for the convenience o f the
Students: For exam ple. Therm odynam ics has been presented in three chapters with titles: Therm odynam ics
I: the First Law, Therm ochem istry, Therm odynam ics II: [he Second and the Third Law, The chapter on
Solution has been divided into Solution and D ilute Solution. E lectrochem istry has been divided into two
chapters: Electrolytic Conduction and Electrolysis, Elecirochemical cells. T he chapter on Reaction Kinetics
has been presented com pletely in a new format. Acids and Bases have been presented as a separaie chapter.
Solubility and Solubility Product form a new chapter. As the m aterial presented in the chapter on Surface
Chem istry and Colloids in the third edition is considerable, this has been split into two chapters: Surface
Chem istry and Colloidal Slate. In many chapters topics have been rewritten with [he inclusion of new

materials and presented in a belter w ay: B rief discussion o f mass spectra, IR and N.M.R. spectra and their
applications are included in ihc chapter on Physical Properties and M olecular Structure. End o f Chapter
Q uestions and Problem s have been revised, many new questions arid problem s with answers have been
incorporated. The format of the book has also been changed.
.
W e hope that the Revised Edition o f the book with its new look will receive the same acceptance by the
students and teachers as the earlier editions.
Printing o f this book has been an arduous task. The publishers are not well acquainted with printing a book
on science with a lot o f Figures and formulae. They have, however, made great efforts to keep the book free
of printing m istakes. W e thank the publishers fur [heir valiant efforts. In spite o f their best intentions you
will find som e errors. W e hope to eliminate these in the future edition.
January, 2009

M. M. Huque


PREFACE TO THE SECOND EDITION

We are gratified to see that the first edition of the book has been well accepied by the students and teachers
in spite o f the numerous printing errors. In the preparation o f second edition attem pt has been m ade lo
increase the clarity of the presentation at several places. The num ber o f numerical exam ples at the end of
[he chapters has been considerably increased. Apart from these changes little has been altered in (he
arrangem ent o f the material and the get up. W e have also tried hard to keep the printing errors at the
minimum.
We are indebted to many o f our colleagues in the universities and colleges who have kindly sent their
criticism s and pointed out the shortcom ings of the first edition. These have been o f great help in making
im provem ent in the clarity of representation.
We are sorry, we could not make ihe book com pletely free of mistakes in spite o f our best wishes.

January, 1971

Dhdka

M. M. H uque
M. A. N aw ab


"

>

. (viii)

PR EFA CE TO THE FIRST EDITION
Printing o f an object by a hundred painters, or writing o f a hundred poetrv on tile same subject need no
explanation, but writing on a book on a subject like Physical Chemistry calls for an explanation specially
w hen excellent books in English are available. D ufing the last many years of teaching Physical Chemisiry
10 the undergraduate students, we have always felt the necessity o f explaining the fundamental conccpls.
W e believe that once the basic principles have been understood by the students, more than halt the battle IS
won. In this respect, there is a need for a book on Physical Chem istry for our students whose background is
different from those for whom the available books are meant. Many o f these books cover fields wider and
deeper thjn what is needed for our undergraduates at the B. Sc. (Pass) level. We, therefore, felt the
necessity o f w riting a book on Physical Chem istry that would fully meet (he requirements o f the B. Sc.
(Pass) students and ai the same tim e help in building a sound background for the Honours students, We
always tried, while writing the book, to explain the basic principles as clearly and elaborately as possible. It
is uptu the teachers who leach the subject and the students who would read to ju d g e whether our aims have
been ÍU[filled.
In the book most portions deal with the kinetic theory, Ihermodynam ics and chemical kinetics. We have
used i.ome final results and equations o f Q uantum Chem istry and did not go anywhere beyond it because
we thought that o m n iu m Chem istry and Statistical M echanics should be treated at a higher level. Although
the approach - has been basically classical attempts have been made to acquaint ihe students with

therm odynam ic approach, tn many placcs both kinetic and therm odynam ic treatment have been used to
show that identical results can be obtained. Only the methodology and physical concept are different.
Q uanlum mechanics! approach has been kepi to minimum, only flashes appear here and there.
In several places we have gone a little beyond than what is expected to form the syllabus o f Pakistani
Universities. The idea is to point to the fact that improvements need be made as is constantly being done in
w estern countries. This is further meani to provide the mental food for [he more serious and above average
students. The average students may leave out the.sc portions on advanced treatment.
Contrary to com m on practice we have not included a chapter on atomic structure and radioactivity. These
two topics generally form a part o f Inorganic Chemistry syllabus in our country and excellent treatment is
available in text books of Inorganic Chemistry. W e therefore, thought it wise to leave oul the branches from
the present volume. This has considerably reduced (he size of the book.
W c express our thanks to a num ber o f our colleagues who always inspired us during the writing o f (he
book. Thanks are specially due to Prof. M. H. Khundkar. Head o f the D epartm ent o f Chemistry, University
o f D haka, for his encouragem ent at various stages. Mr. A. J. M ahm ood. Senior Lecturer in Chemistry.
U niversity o f D haka, deserves special thanks for kindly going through a large portion o f the manuscript and
m aking valuable suggestions. Thanks are also due to Mr. A N, M. Akhter, a student o f the Dhaka College,
for draw ing a number of original sketches and helping in making the design o f the dust cover. We are
indebted to Mr. M esbahul Haque for preparing the index. We must also thank Mr. Sycd Md. Fazlul Huq of
the S tudents' Publications for taking the task of publishing the book. Mr. A. K. M. Raja Meah deserves
special m ention Cor his untiring efforts and hard work in the printing o f the book.
G ood printing is a challenging task and in spite o f our best efforts som e mistakes are still there. We
apologise for this and hope to im prove in the next edition. We shall appreciate receiving com m ents from
those w ho use the book, so that im provem ents can be made in future.

D epartm ent o f Chemistry
U niversity of Dhaka
Ju n u jfy . 1968

M. M. Huque
M. A. Nawab

(ix)

CONTENTS
S T A T E O F A G G R E G A T IO N O F M A T T E R IN T E R M O L E C U L A R F O R C E S
1.1

Matter: States o f Aggregation

1.2

lnterm olecular Forces

1.3

Hydrogen bondi

'

I

_

4

8

11

QUESTIONS AND PROBLEM S

12-76

T H E G A SE O U S S T A T E
2.1
Ideal G ases: T he G as Law s

12

12

2.2

B oyle's Law

2 3

C h a rle s’ Law o r G ay-L ussac's Law

2.4

The A bsolute Z ero o f T em p eratu re

2.5

A vogadro's L aw

2.6

The Ideal Gas E quation

2.7

The Significance o f R

2.8
29

Page
4 -1 1

15'
‘ 17
17

■

18
18
19

T he N um erical V alue o f R
T he Use o f the G as E quation in C a lcu latio n s In v o lv in g G ases

20

D iffusion and E ffusion: G raham ’s Law ot D iffusion

21

2 11

E quation o f S tale o f a G as M ixture: D alto n 's Law OÍ P a rtia l P re ssu re

22

2.12

T he K inetic T heory o f G ases

2.13

R o oi-m ean-square (r.m .s.) V elocity

2.14

D erivation o f the K inetic E quation

2.15

D eduction o f the G as Law s from the Kinetic E quation

2.16

M olecular V elocities

2.17

D istribution o f V elocities

2.18

Average Velocity, r.m.s. Velocity and Most Probable Velocity

2.19

Mean Free Path

2.20

V iscosity of G ases

2.21

M o lecular D iam eter

2-22

Frequency o f C ollisions o f Gas Molecules

2.23

N um ber o f M olecules Striking a S urface

2.24

A vogadro N um ber

2 25

The Kinetic T heory - a review: Brow nian M ovem ent

f 26
r2 7

B ehaviour o f R eal G ases: T he A m agat s C u rv es
Modification of the Ideal Gas Equation: van der W aals' Equation o f State

2 -’8

Significance and L im itations o f van der W aals E quation

2.29

O ther Equations o f S tate

2.30

Change of State: G as-Liquid Transition

2.31

A ndrew s’ E xperim ents with C O ;

10

24
25
25

27
.

29
30
31
32
33
33
34
35

>

35
36
37
38
41
43
43
44


00

2.32

D eterm ination o f C ritical C o n stan ts

2.33

van d er W aals E quation and the C ritica l P henom ena

48

2-34

C on tin u ity o f S tate

50

2.35

The E quation o f th e C orresponding States

2.36

L iquefaction o f G ases - the B asic P rinciples

46

.
.

2.37

M ethods o f A ttain in g Low T em p eratu re

53

2.38

Uses o f Liquefied G ases

57

2.39

Density o f Gases and M olecular M ass

57

2.40

A bnorm al D ensities o f G ases; M o lecu lar A sso ciatio n and D isso ciatio n

64

2.41

Heat Capacities o f Gases: Definitions

68

2.42

H eat C apacity and K inetic T heory

2.43

Experimental D eterm ination o f Ỵ o f a Ga>

2.44

The Principle o f Equipartition o f Energy

68
'
’

74

T H E L IQ U ID S T A T E
3.1

77-93

Vapour Pressure o f Liquids

77

3.2 ' Kinetic Theory o f Vapour Pressure

78

3.3

Va po ur Press ure a nd Tem perat lire

79

3.4
3.5

Boiling Point of a Liquid: E nthalpy o f V aporization
Trouton's Rule

80
go

3.6

M easurem ent o f Vapour Pressure

81

3.7

Surface Tension

83

3.8

Adhesion and Cohesion

85

3.9

M easurem ent o f Surface Tension

g5

3.10

Surface Tension and Tem perature

89

3.11

T he Viscosity o f Liquids

89

3.12

The Poiseiiille Equation

J. 13

M easurem ent o f Viscosity

3.14

Viscosity and Tem perature

3.15

Viscosity and Its Im portance

3.16

Structure o f Liquid:,

•

S9
90
92
92
,

92

Q UESTIONS AND PRO BLEM S

4

70
72

QUESTIONS AND PROBLEM S
3

51
52

93

T H E S O L ID S T A T E

94-119

4.1

Preparation o f Crystals

94

4.2

Bonding in Crystals and their C haracteristic

96

4.3

Internal Structure o f a Crystal

4.4

Sym m etry in Crystals

4.5

The Crystal System s

97
101

■

»

10"?


■

( x i)
.

103

4.6

X-rays and Diffraction o f X-rays by Crystals

4.7

Cubic Lattices

Ỉ 05

4.8

The Structure o f Sodium Chloride Crystals

108

4.9

T he Pow der M ethod

108

4.10

Application o f X-ray D iffraction

109

4.11

Conductors, Insulators and Sem iconductors

109

4.12

Defects in Solids

113

4.14

Liquid Crystals

1 IS

4.15

The Specific Heats o f Solids

1i 7

4.16

Isomorphism

,

J IS

QUESTIONS AND PROBLEM S

1)9

120-142

T H E R M O D Y N A M IC S I : T H E F IR S T L A W

120

5.1

The Nature o f Therm odynam ics

5.2

Important Concepts in Therm odynam ics

5.3

The First Law o f Therm odynam ics

125

5.4

Mathem atical Form ulation o f the First Law

126

5.5

Therm odynam ic Processes

127

5.6

Work o f Expansion

129

5.7

Isothermal Reversible Expansion of an [deai Gas: M aximum W ork

129

5.8

Constant Volume Processes

132

5.9

Partial Differential Notation

132

5.10

Constant pressure Processes and Enthalpy

132

5.11

Relationship between u and H

133

5.12

H eal Capacity and M oiar H eat Capacity

134

5.13

The Internal Energy of an Ideal Gas: Joule's Experim ents

138

5.14

Jouie-Thom son Porous Plug Experiments

138

5.15

Adiabatic Processes

.

Q UESTIONS AND PROBLEM S

T H E R M O C H E M IS T R Y

121

141

' 142

143-170
143

6.1

Heat o f Reaction or Enthalpy of Reaction

6.2

Conventions

6.3

Heat o f Reaction at Constant Pressure and at Constant Volume

145

6.4

The Determination o f Heats o f Reaction: Calorim etry

146

6.5

Enthalpy of Com bustion: Bomb Calorimeter

146

6.6

Laws of Therm ochem istry

6.7
6.8

Heal o f Formation
Effect o f Tem perature on Heat o f Reaciion: The K irchhoff Equation

6.9

Enthalpy o f Solution

144

149
153
155
156


(x.i)
6.10

Heat o f Neutralization

158

6.11

Enthalpy Change during Phase Change

160

6.12

Calculation o f Heat of Reaction: Bond Energy

160

6.13

Enthalpy o f Ionization or Ionization energy

164

6.14

Electron Affinity

165

6.14

The Lattice Enthalpy (L.E.)

165

QUESTIONS AND PROBLEM S

168

T H E R M O D Y N A M IC S I I : S E C O N D AND T H IR D L A W S
7.1
Necessity o f the Second Law
■

171-201
171

7.2

Spontaneous and Non- spontaneous Processes

7.3

Heat Engine

172

7.4

Statement o f the Second Law

173

7.5

The Carnot Cycle

174

7.6

Entropy - A N ew Therm odynam ic State Function

177

7.7

Entropy and equilibrium

182

7.8

Entropy C hange o f an Ideal Gas

182

7.9

Calculation o f AS for Physical Processes

184

7.10

The Third Law o f Therm odynam ics

187

7.11

Entropy and M olecular Chaos

188

7.12

171

The Free Energy and the Work Function

190

7.13

G ibbs-He!mholtz Equation

196

7.14

Equilibrium between Phases : T heC lapeyron Equation

197

7.15

The Clausius-Clapeyron Equation

199

QUESTIONS AND PROBLEM S

201

S O L U T IO N S

202-225

8.1

Types o f Solutions

203

8.2

Units of Concentration

203

8.3

Solution o f Gas in Liquids

205

8.4

Effect of Tem perature

206

8.5

Influence of Pressure

206

8.6

Validity and Lim itations o f Henry's Law

208

8,7

Solution o f Gas in Solid

208

S.8

Liquid - Liquid Solution: T he Solution Process

209

8.9

Ideal and Non - ideal Solutions

211

8.10

Solid - Liquid Solution; The Solution Process

8.1 i

Solubility

8.12

Effect o f Tem perature on Solubility

214

8.13

Distribution of a Solid between Two Immiscible Liquids : T he Distribution Law

216

211
■

■ 213


(xiii)
8.14

Deviations from D istribution Law

8.15

Applications o f Distribution Law

8.16

Solvent Extraction

917

‘'
220

222

.

225

QUESTIONS AND PROBLEM S

D IL U T E S O L U T IO N S : C O L L 1 G A T IV E P R O P E R T IE S
9.1

Lowering of V apour Pressure

9.2
9 3

Ideal Solution
M olecular Mass from Low ering o f Vapour Pressure

'

9-4

226-254
226
228
228

_Derivation o f Raoult's, Law •

Ộ.5

M easurem ent of Low ering.of Vapour pressure

9.6

Elevation of Boiling Point

°29
,

231

■

9.7

Therm odynam ic D erivation o f Boiling Point Elevatiốn

233

9 8

Determination of M olecular M ass from Boiling Point Elevation

235

9.9
9.10

Depression of Freezing Point
Thermodynamic Derivation o f the Freezing Point Depression

9 11

M easurem ent of Depression o f Freezing Point

237

238
240
241

■

9 12

Osmosis and Osmotic Pressure

9.13

Semi-permeable M embrane

9 14

Determination of O sm otic Pressure

9 15
9 .16

Van't H offs Laws o f Osmotic Prer.i-Iire
D eterm ination o f M olecular M ass from Osmotic Pressure M easurem ents

9 17

Thermodynamic D erivation of’ O sm otic Pressure Laws
•
Relative Osmotic Pressure

9 .18
9.19

Interrelation between the Colligative Properties

9.20

Abnormal M olecular M asses from Colligative Properties ’

9.21

Importance of Osmosis Phenom enon

C H E M IC A L E Q U IL IB R IU M
10.1
10.2
. 10.3
10.4

242

■

_

QUESTIONS AND PROBLEM S

10

229

Reversible Reactions
The Equilibrium Law: the Equilibrium Constant
Gaseous Equilibria
Relation between K., and K,

10.5

Determination o f Equilibrium Constants

10.6

Criteria o f Chemicai Equilibrium

] 0.7

Activity and Activity Co-efficient

to .8

Calculations Involving Chemical Equilibrium

10.9

Homogeneous Equilibria

10.10 Equilibria in Solution

"Mi
246

248

■

249
250
252
252

255-283
255
257
260

261
262
262
263
264
264
269


10.í 1 Heỉerogerteous Equilibria
10.12 Factors influencing Equilibrium : The Principle o t'L e C hạielier
10.13 A pplications o f the Principles o f Chemical Equilibrium 10
Reactions o f Industrial Im portance
10.14 Free Energy Change and Equilibrium Constant
10.15 Influence of Temperature on Equilibrium Constant: Thermodynamic Derivation
QUESTIONS AND PROBLHMS

P H A S E E Q U IL IB R IA
111

Definition o f Terms

11.2

Deduction o f the Phase Rule

.11.3

W ater System

11.4. The Suiphur System
11.5

Phosphorus System

11.6

Sublimation and Triple Point

11.7

Solid-liquid Equilibria: Eutectic Point

11.8

Liquid-Liquid System s

11.9

Fractionating Column

11.10 Com pletely M isibte Liquid Pairs Showing D eviation from R aoult’s Law
11.11'D istillation o f Non-idea] Solutions : Azcofropic M ixture
11.12 L iquid-L iquid Equilibria in Partly M iscible System s :
Critical Solution Tem perature (CST)
11.13 Immiscible Liquid Pairs: Steam D istillation
Q UESTIONS AND PROBLEM S
K IN E T IC S O F C H E M IC A L C H A N G E
12. i

The Definition o f Rate o f a Reaction

12.2

Experimental D eterm ination o f the Rate o f a Reaction

12.3

Factors A ffecting the Rates o f Reaction

12.4

Dependence o f Rate on Concentration: T he Raie Law

12.5

Units o f Rate Constants

12.6

Determination o f the Rate Law: D eterm ination o f Order o f Reactions

12.7

Some Typical Reactions

12.8

Complex Reactions

12.9

Influence of Tem perature on Reaction Rates

12.10 Collision Theory o f Reaction Rates
12.

[Ỉ Transition State Theory

12.12 The Rate Law and M echanism o f Reaction
12.13 M oiecularity and Order o f Reactions
i 2 .14 Unimoiecular Reaction: Lindem ann's M echanism


(XV)
*

12 15 Theory o f Absolute Reaction Rate
1 2 . 16. Hydrogen-Chlorine Reaction
12.17

3 4 7

ỉ5 0

Branching Chains: Explosive Reactions

3 _0

12.IS H ydrogen-O xygenReaction

.

352

12-19 Absorption of Light: Beer-Lambert Law

254

12 '’O Consequences o f the Absorption ot Light

^

12.21

Lum inescence

.

p .2 2 The Law s of Photochem istry

358

12 23 D eterm ination o f Q uantum Yield
12.24 Photosensitized Reaction
12.25 Photosynthesis

3(30

12 °6 Radiation Chem istry
12.27 Gas - Solid System s: Reactions Involving One Gas

262

12.28 Gas-Solid System s: Reactions Involving Several G ases

3^3

I') 29 H eterogeneous Reactions in Solution
q u e s t io n s a n d p r o b l e m s

366-378
13

C A T A L Y S IS

366

13.1
Definition
13.2 Types o f Catalysis
13.3 Characteristics o f Catalysts
13 4

Energy Changes in Catalytic Reactions

13 5

Prom oters and Catalytic Poisons

13 6

Theories o f M echanism o f Catalysis

13.V Acid-Uiise C atalysis
13.8 M e c h a n i s m o f Acid-Base Catalysis

'

366
36 g
J7 Q
^ J
275

.

.

13.9 Enzyme Catalysis
13.10 M echanism o f Enzym e Catalysis

375
377

QUESTIONS AND PROBLEM S
14

379-409
™

ELECTRICAL C O N D UC TA N C E AND ELEC TR O LYSIS
14.1

Electrolytic Conduction

14.2

M etallic and Electrolytic Conduction

14.3 Electrolysis
14 4 T he M cchanism o f Electrolytic C onduction
14.5
14.6
14 7

.

219
?80
381

,

Faraday's Laws o f Electrolysis
Faraday and Sipr.ificance o f the Faraday’s Laws
The Conductance o f Electrolytic Solutions

3g4
3g5

14.8

E x perim en tal D eterm in atio n o f C o n d u ctan ce

3g9

14.9

Conducianee Ceil: Cell Constant


( XVI )

14.10 Conductivity Water

390

14.1 i Conductance and Electrolyte Concentration

391

14.12 The Conductance Ratio

392

. 14.13 Debye-Hiickel’ Onsagcr Theory

393

14.14 Independent M igration o f Ions: K ohlrausch's Law

395

14.15 Absolute Velocity o flo n s: Ionic M obility

397

14.16 Applications o f C onductance M easurem ents

399

14.17 Transport Number {or Transference Number)

402

14.18 M easurem ent o f Transport N um ber

405

14.19 Factors Affecting Transport N um bers

408

QUESTIONS AND PRO BLEM S
15

408

E L E C T R O C H E M IC A L C E L L

410-452

15.1
15-2

Galvanic Cells
The O rigin o f E.M.F. at M etal-Solution Interface

Vi 10
41!

15.3

Reversible and Irreversible Cells

15.4

M easurem ent of E .M .F o f Elecirocheinical Cells

413

15.5

W eston Standard Cell

414

15.6

Types of H alf-Cells

415

■

412

15.7

Single Electrode Potential: Standard Hydrogen Electrode

417

15.8

Secondary Standard Electrodes

41§

15.9

Electrochemical Cells; Notations and Sign Convention

419

15.10 Determination o f Standard E lectrode Potential (SEP)

421

15.11 Values o f Standard Electrode Potentials

422

15.12 Uses o f Standard Potential Values

424

15.13‘Effect of C oncentration and Tem perature on Electrodc Potential: The Nernst Equation
15.14 Determination of pH o f a Solution

430

15.15 Therm odynam ics and E.M.F. o f Cells

433

15.16 Liquid Junction Potential: Salt Bridge

439

15.17 Types o f Galvanic Cell

439

15.18 Application o f E.M .F. M eạsurem enls

443

15.19 Lead Storage Cel]

447

15.20 Leclanche's Dry Cell

447

15.21 Fuel Cell

447

15.22 Polarization and O vervoltage

449

15.23 The Polarograph

QU ESTIO N S AND PRO BLEM S
16

426

A C ID -B A S E E Q U IL IB R IA

:

.

450
451
453-493

16.1

A cids and Bases:, the Arrhenius concept

453

16.2

B ronstẹđ-L owry concept

454


( x v ii)
16.3

The Lewis Concept

456

16.4

Self-Ionization (or auto ionization) o f W ater

457

16.5

Hydrogen ion concentration -T h e pH Scalc

438

16.6

Some useful relationship

16.7

M easurem ent o f pH

.

461
462

16.8

Dissociation o f weak acids and weak bases: O stw ald’s D ilution Law

465

16.9

Dissociation constants o f weak acids and weak bases

466

16.10 pH o f solutions o f very weak acids
Ỉ6 .1! pH o f solutions o f very weak bases

469

!6 .12 The Com mon [on Effect

1

16-13 Indicators in Acid - Base Tiiraiions

472

16.14 Acid -Base Titrations: Choice o f Indicator for Titrations

474

16.15 Titration o f a Strong Acid with a Strong Base

*75

16. J6 Titration o f a Weak Acid with a Strong Base

476

16.17 Buffer Solutions
16*18 Salt H ydrolysis
16.19 The pH o f Salt Solutions
16.20 Amphoteric Elecưolytes: Zwiitcr Ions
QUESTIONS AND PROBLEMS

17

SOLUBILITY ANDCOMPLEX-ION EQUILIBRIA
17.1

491
49 *

Solubility and Solubility Product

«M-50S

*

17.2

Solubility and Common !on Effect

17.3

Effect o f pH on Solubility

17.3

Predicting Precipitation

17.4

Applications o f Solubility Product Principle

,
502

17.5 Equilibria of Complex Ions
QUESTIONS AND PROBLEMS
18

...................

SURFACE CHEM ISTRY
18.1

T he Nature o f Surfaces

ĨS.2

Definition o f Terms

18.3

Nature o f Adsorption

J8-4

Gas-Solid Systems: Lanomuir Isotherm

.
fro ill Langniuir Isotherm

18.5

Deviations

18 6

B E T (B run au er, F m m e t an d T eller) Iso lh ern i

18?

Gas-Liquid Interface: Surfacc Film and Surface Pressure

15.8

Gibbs' A dsorption Equation

15.9

Adsorption from Solution

505

«Mfc.«22

508
"

513
514

515
’
517


( x v iii)
18.10 Freundlich Isotherm

519

18.11 Langm uir Isotherm for Solid-Liquid Adsorption

519

18.12 Chrom atography

520

QUESTIONS AND PRO BLEM S
C O LLO ID S AND EM U LSIO N
19.1

Crystalloids and Coiloids

523-541
■

523

19.2

Disperse Phase and Dispersion M edium

19.3

Types of Colloids

.

524
524

19.4

Soi and its Preparation

525

19.5

Purification o f Colloids: D ialysis and Electrodialysis

528

19.6

Lyophobic and Lyophilic Sols

529

19.7

Properti es o f Colto ids

531

19.8

Stability o f Colloids

536

19,.9

Peptization

537

19.10 Gel

537

19.11 Syneresis

537

19.12 Imbibition and Swelling

538

19.13 Foam

538

19.14 Colloidal electrolyte

538

19.15 Em ulsion

539

19. tó Importance o f Colloids

540

QUESTIONS AND PRO BLEM S
20

54 i

PHYSICAL PR O PER TIES A N D M O LEC U LA R STRUCTURE

542-568

20.1

M olar Volum e

542

20.2

Pai'achor

543

20.3

Kefracti ve Index and M olar R efraction

20.4

O ptical Activity

545
■

546

20.5

D ipole M om ent and M olecular Structure

549

20.6

Spectroscopy and Molecular Structure

552

Q UESTIONS AND PRO BLEM S

568

INDEX

569-574

2-B

19

522


State of aggregation of m a tte r: Interm olecular forces

1

1

STATE OF AGGREGATION OF MATTER
ỈNTERMOLECULAR FORCES

1.1 Matter: States of Aggregation
Under ordinary conditions all material bodies exist in one of the three states of
aggregation-solid, liquid or gaseous. Apart from these well known states matter is also
found to exist in three other states, e.g. liquid crystals, giass and an unusual state under
special conditions called the plasma state. Each state is characterized by some specific
properties. For example, solids have definite shape and size and these are incompressible.
On the other hand, liquids do not possess any definite shape or size. It takes the shape of
the container in which it is placed. Liquids are also only slightly compressible. Gases are
highly compressible. When placed in a container a gas completely fills it, that is to say,
gases do not have a definite volume. A common characteristic of solids, liquids and gases
is that these expand when heated at constant pressure, but the amount of expansion is
much more ill Ihe case of a gas than in the case of a liquid or a solid.
ĩn describing the nature of matter Ihe atomic molecular theory of matter has been
universally accepted. According to this Iheory the smallest particle of all elements is
culled atom. Atoms o f the same element have the same characteristic structure and
properties. The structures and properties of atoms of different elements are different. The
molecule is defined as the smallest particle of matter which can exist independently.
Molecules of most substances are composed o f two or more atoms of the same or
different elements. Examples are molecules of nitrogen, N 2 , or carbon dioxide, CŨ 2 Molecules of the rare gases like helium, argon etc. and those of mercury are made up of
one atom and hence are called monatomic. The physical and chemical properties of a
substance are the sum of the properties of all the molecules of which it is composed.
A substance may exist in all the three states of aggregation under different

conditions of temperature and pressure, but it has the same molecules. The effect o f
heat on a oiece o f ice may be taken as an example. When heated, ice melts to form
liquid water. On heating further liquid water is converted into steam or water vapour.
Heat is a form o f energy and ever since the days of Count Ruml'ord heat energy has
been related to motion. When motion is increased more heat is produced or,
conversely, when heat energy is added to a substance, i.e., the substance is heated
motion increases. The question is motion o f what increases as a result of heating? ]n
trying to answer this question it. was soon realized that it must be the motion o f the
molecules that increases on heatirg ■’ hodv Thi’ k’i'=vtic rrtoleculi!" theory of matter


Principles of Physical Chemistry
look ils birlh. The molecules may execute any one or more of the three possible types
of motion, namely, translational, rotational and vibrational (Figure 1.1). Translational
motion consists in movement from one position to another. For rotational and
vibrational motion displacement o f the molecule is not necessary. Rotation of the
molecule may take place around any of the different axes, whereas vibration of the
molecule may take place around a mean position.

Figure 1.1 (a) Rotation of molecules; (b), (c) and (d) Different types of vibration
Based on the atomic molecular and kinetic molecular theory of matter the
characteristics of the three states of matter may be summarized as follows.
ỉn the solid state the molecules or ions are fixed in a uniform manner in definite mean
positions in the solid state. There are strong intermoỉccular (or inter-ionic) forces which
keep the molecules (ions) in their positions in (he lattice. The only type of movement that
the molecules may undergo is vibration around their fixed mean positions. The resulting
structure is a fairly rigid one, having a definite shape and a definite volume, which
strongly resists compression, expansion and distortion.
In the liquid state the molecules or ions have more energy. They have sufficient
energy to overcome ihe forces which hold the particles in their positions in the solid state.

As a result ths molecules or ions possess translational motion but within a limited range,
as the energy is not so high as to enable them to overcome the attractive forces altogether.
The liquid state is, therefore, such that in this state it has a definite volume but not a
definite shape. As ihc molccules (or ions) cannot escapc far from each other the
compressibility of a liquid is high. In the liquid state the molecules (ions) also possess
rotational and vibrational energy.
When the molecules have sufficient energy which enables them to completely
overcome the attractive forces the molecules form Ihe gaseous state of matter. In the
absence o f the attractive forccs molecules can move about in a random manner within the
container at high speeds. As a result, they distribute themselves uniformly throughout the
whole volume o f the container. A gas, therefore, has no definite shape or volume. In the
gaseous state the molecules are far apart from one another, and the volume within which
the gas is confined is almost empty space. This explains why the gases are so highly
compressible. When pressure is exerted the volume of the gas decreases, i.e., the
molecules get closer. In addition to translational energy molecules in the gaseous state
also possess rotational and vibrational motion.


State o f aggregation of m a tte r: Interm olecular forces

3

The conversion of solid to liquid and that of liquid to gas takes place on the
application of heat. The reverse process of converting a gas into a liquid may be
accomplished by compressing the gas (so that the molecules are very close) and cooling
so that the molecules have lesser energy than required to overcome the forces OÍ
repulsion On further cooling, the translational energy may be decreased to such an extent
that the attractive forces will hold the molecules in fixed positions, i.e., the solid state is
reached. Ill solids, therefore, the particles are very d o s e to each other, in liquids they are
close but not very close, but in gas they are widely apart. This is shown in Figure 1.2 as a

pictorial representation.

Solid
Figure 1.2 Schematic representation of gas, liquid and solid
It should be noted that solids may also be converted to the gaseous state w ithout
passing through the intermediate liquid state by application o f heat. Such a process
is known as sublimation. The above arguments may be given for such
transformation. Changes o f states are, therefore, reversible processes as show n in
Figure 1.3.

Solid

Figure 1.3 Reversibility between three states of matter
When solids are converted into liquids, intermediate phases possessing some of the
molccular order characteristic of crystalline solids are sometimes obtained. These
intermediate phases are called liquid crystals (Section 4.14.1) bccause they possess some
of the properties of both solids and liquids.


4

Principles o f Physical Chemistry

Glasses are amorphous substances which have the properties of a solid but the
structure of a liquid. Although apparently solid, structurally they resemble liquids as their
constituent particles are found Lo be randomly Arranged. Glasses are amorphous, meaning
without shape*. These are, in fact, liquids coolcd below their freezing points without
crystallization taking place. These arc regarded as supercooled liquids and are considered
as intermediate between liquid and solid.
'

Plasm a is an ionized gas formed when high temperature strips electrons from atoms.
Plasma is an electrically neutral mixture of electrons and positive ions. It exists in the sun
where nuclear fusion takes place. Over 99% o f the matter in the universe, in stars and
galaxies, seems to exist in the form of plasma. The sun and stars consist o f matter in the
form ot highly ionized plasmas formed at verv high temperatures.

1,2 Interroofecular Forces
In the above paragraphs mention has been made o f intermolccular (or inter-ionic)
forces. One might ask ‘what is the origin of these forces'? We have to remember that
atoms and molecules are made up OÍ only protons, electrons and neutrons. Of these,
prnlons in the nucleus are positively charged, electrons are negatively charged and
neutrons do not carry any charge. These are particles with very small mass. As the effect
o f gravitational attraction between particles of such small mass is extremely small and
negligible, one can only think that the forces between particles must be electrical in
nature. The melting point and the boiling point o f a substance are measures of the
strength oi such forces. The higher Ihe melting and boiling points stronger must be the
attractive forces between particlcs, i.e. ions or molecules.
From the study of the nature of these forces it has emerged that there are different
types o f forces between particles. These forces arc listed below :
(a) Ionic interactions
(b) van der Waals forces

V

(i) P ipoie -dipole interactions
(ii) Dipole-induced rtipple interactions
(iii)Dispersion forces (instantaneous dipole-induced - induccd dipole interaction)
(ivjHydrogen bonding.
As an approximation the relative strengths of these forces can he summarized as follows:
Table 1.1 Relative stren g th s of inter-particle forces

Type o f interaction

Relative strength

Ionic bonds

1000

Hydrogen be rids
Dipole-dipoie
Dispersion

100
10
1


State o f aggregation of matter : Interm olecular forces

5

(a) Ionic Interactions
Electrostatic interactions occur between ions resulting in the form ation of strong
ionic bonds. These bonds are formed when metals atom s transfer their valcnce
electrons to non-metal atoms forming positively charged metal ions (cations) and
negatively charged non-metal ions (anions). The oppositely charged ions attiact
each other forming a three dimensional giant rigid structure in the solid state. Ionic
com pounds have high melting and boiling points as large am ount oi energy IS
required to overcome the electrostatic forces o f attraction between the charged ions.
In the molten state they are good conductors of electricity as the ions becom e free

and mobile.
In cases where a small cation with large charge combines with an anion having a
large size the resulting compound may have some covalent characters. Examples are,
M gBr2, FeCh, A ll 3 etc. There are examples (anhydrous ferric chloride, anhydrous
aluminum chloride) of compounds between metals and non-metals which are completely
covalent.
Metal atoms are held together by strong metallic bonds.

(b) van der W aals Forccs
(i) Dipole - dipole interactions : Dipole-dipole interactions were first described by
Willem Hendrick Keesom in 1921.
These are the forces that occur between two polar m olecules w ith perm anent
dipole moments. D ipole-dipole attractions are electrostatic in nature like the ionic
bonds but are weaker because only partial charges are involved. An exam ple o f this
type o f interactions can be seen in the hydrogen chloride molecules. In a H Cl
molecule there is large difference in electronegativity betw een H atom and Cl atom
(Cl is much more electronegative than H ) and the electron pair between these tw o
atoms in h i Cl molecule is attracted more strongly by Cl atom than by the H atom.
This unsymmetrical (unequal) distribution of the electron pair betw een the
combining atoms give rise to partial positive charge (5+) on the H atom and partial
negative charge (S') on the Cl atom. As a result a dipole is formed, and the molecule
is called polar. When two polar H Cl molecules are close together a structure sim ilar
to the one shown below is formed.
Ò+

Ó-

H— Cl.........H— Cl

In a polyatomic molecule if the bond polarities do not cancel each other then the

molecule has an overall polarity. This can happen because the symmetry in shape of the


fi

Principles o f Physical Chemistry

molccule. Examples are H 2 O and B F j molecules. Water is polar, but BF 3 is non-polar as
shown b e l o w :
F S“

Figure 1.4 Shapes of H;0 and BFj molecules
As can he seen, the bond polarities in BFi cancel each other, because of the
symmetrical planar shape o f the motccule. In water, however, o - H bond polarities do
not c a n e d as the molecule has a he 111 shape.
(H) D ipole-iwlticttl dipotc in teractions : Dipole-induced dipole interaction involve
(he attraction belwcen temporarily induced dipoles in non-polar molecules. This
pof dilution can be induced either (a) by a polar molecule or (b) by the repulsion of Ihe
negatively charged electron clouds in a norvpolar molecule. An example of the former is
chlorine dissolving in water.
(Í+ )

< £ -)

(d+> ■

tử’- )

[Permanent dipole] H - o - H --------- Cl - Cl [Induced dipole]
This is an example o f interaction between the permanent dipole of water molecule
and iiO induced dipole on chlorine molecule. The dipole in non-polar chlorine molecule is
induced by the electric field offered by (he permanent dipole of water molecule. This
permanent diooJe -induced dipole interaction is referred to as induction (or polarization)
interaction and is to be distinguished from London dispersion interaction.

Oil) Induct'd dipole-iml um l dipule fore© (London forces or dispersion forces)
The above ideas of intcrmoỉecuiar forcc are unable to explain why molecules which
do not have dipoles and noble gases like argon, xenon etc. can be liquefied and solidified.
Strong attractive forces must exist between the molecules or atoms (in case o f noble
gases) to keep the particles together in these states.
l.ef us take the exam ple o f a Xenon atom. The electron distribution about the
nucleus o f a Xe utom is perfectly spherical. However, the electrons are constantly in
motion and it is possible that at any given instant in some o f the Xe atoms all the
electrons may be positioned on one side o f the nucleus, temporarily giving rise to
partial positive charge ai one end o f the atoms and a partially negative charge on the
other side. As a result an instantaneous dipole is formed in these Xe atoms. During
this transitory existence the instantaneous dipole is likely to induce a dipole in a