An Introduction to Chemical Kinetics

Michel Soustelle

• Publisher: Wiley-ISTE
• Year: 2013
• Print ISBN: 9781848213029
• eBook ISBN: 9781118604229
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Physical & Theoretical Chemistry

This book is a progressive presentation of kinetics of the chemical reactions. It provides complete coverage of the domain of chemical kinetics, which is necessary for the various future users in the fields of Chemistry, Physical Chemistry, Materials Science, Chemical Engineering, Macromolecular Chemistry and Combustion. It will help them to understand the most sophisticated knowledge of their future job area.
Over 15 chapters, this book present the fundamentals of chemical kinetics, its relations with reaction mechanisms and kinetic properties. Two chapters are then devoted to experimental results and how to calculate the kinetic laws in both homogeneous and heterogeneous systems. The following two chapters describe the main approximation modes to calculate these laws. Three chapters are devoted to elementary steps with the various classes, the principles used to write them and their modeling using the theory of the activated complex in gas and condensed phases. Three chapters are devoted to the particular areas of chemical reactions, chain reactions, catalysis and the stoichiometric heterogeneous reactions. Finally the non-steady-state processes of combustion and explosion are treated in the final chapter.

PART 1

Basic Concepts of Chemical Kinetics

Chapter 1

Chemical Reaction and Kinetic Quantities

This first chapter devoted to chemical kinetics, should provide us with definitions of specific notions that are the extents and speeds of reactions every time we approach a new field of disciplinary paradigms. This description is particularly important in chemical kinetics because many definitions are intuitively related to the evolution of a reaction system and the speed of this evolution and for which the same word does not always correspond to the same definition according to authors. Thus we encounter many “speeds” of reaction that are not expressed in the same units and are not always linked with each other. The result is such that when starting to read a book – or an article on kinetics – the reader needs to pay particular attention to definitions given by the author if indeed he or she has taken the trouble to explain them. Therefore we specially draw the reader’s attention to this chapter.

1.1. The chemical reaction

1.1.1. The chemical equation and stoichiometric coefficients

A chemical reaction is the phenomenon that turns an unstable chemical species or mixture, under the conditions of chemical experiment, into other stable species. A reaction is represented by its chemical equation such as reaction [1.R1], which represents the reaction between nitric oxide and hydrogen, and produces water and nitrogen:

[1.R1]

This chemical equation, besides the chemical species being involved, includes numbers placed in front of each species (e.g. 2 for N2) that are called the arithmetic stoichiometric coefficients. The set of coefficients belonging to a reaction may be multiplied or divided by the same number without modifying the reaction in any way. For example, the above reaction could also be written by multiplying all the stoichiometric coefficients by two in the following:

These coefficients (integer or fractional) indicate the proportions of species that are involved in the reaction. For example, in reaction [1.R1] if three moles of nitric oxide react with three moles of hydrogen respectively, in fine, when the reaction is totally complete it will have produced three moles of water and 1.5 moles of nitrogen.

NOTE 1.1.– During the kinetic study (as for the thermodynamic study) of a reaction, it is recommended we choose a set of stoichiometric coefficients and keep them. It is highly recommended to choose the same series for the kinetic and thermodynamic study that often precedes it.

We state that the chemical equation is a “molar” equation and it should be noted that the two members of the equation are separated by the equals sign.

In the case of certain generalizations it is sometimes usual to represent equation [1.R1] as [1.R2], which is obtained by passing all the initial chemical species to the right-hand side through the application of the algebraic rule of change in sign:

[1.R2]

The new coefficients 2, 1, -2 and -2 are called algebraic stoichiometric coefficients. It should be noted that they are positive for a product of the reaction and negative for a starting compound.

GENERALIZATION.– A reaction between the compounds A1, A2, […], Ai… producing species A′1, A′2 […], A′j will be generally written as [1.R3], with the arithmetic stoichiometric coefficients βk or as [1.R4] with the algebraic stoichiometric coefficients νk:

[1.R3]

[1.R4]

with the relations:

– νi = − βi for a species that reacts; and

– νj = βj for a species that is produced.

NOTE 1.2.– Some physical transformations are treated as reactions and can be represented by a chemical equation. For example, let us quote state changes like the fusion of ice in water, which can be written as:

or the diffusion of a species A from one point to another within a solution and that will be represented by:

It should be noted that physical t...

Table of contents

• Cover
• Title Page
• Copyright
• Preface
• Part 1: Basic Concepts of Chemical Kinetics
• Part 2: Reaction Mechanisms and Kinetic Properties
• Appendix
• Notations and Symbols
• Bibliography
• Index