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An Introduction to Chemical Kinetics

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An Introduction to Chemical Kinetics An Introduction to Chemical Kinetics Michel Soustelle WWIEY Table of Contents Preface xvii PART 1. BASIC CONCEPTS OF CHEMICAL KINETICS 1 Chapter 1. Chemical Reaction and Kinetic Quantities 3 1.1. The chemical reaction 3 1.1.1. The chemical equation and stoichiometric coefficients 3 1.1.2. The reaction components 5 1.1.3. Reaction zones 6 1.2. Homogeneous and heterogeneous reactions 8 1.2.1. Single zone reaction 8 1.2.2. Multizone reaction 8 1.3. Extent and speed of a reaction 9 1.3.1. Stoichiometric abundance of a component in a reaction mixture 9 1.3.2. Extent of a reaction 9 1.3.3. Speed of a reaction 11 1.4. Volumetric and areal speed of a monozone reaction 12 1.5. Fractional extent and rate of a reaction 14 1.5.1. The fractional extent of a reaction 14 1.5.2. Rate of a reaction 16 1.5.3. Expression of the volumetric speed (areal) from variations in the amount of a component 16 1.6. Reaction Speeds and concentrations 18 1.6.1. Concentration of a component in a zone 18 1.6.2. Relationship between concentration and fractional extent in a closed environment 19 vi An Introduction to Chemical Kinetics Exprn f vltr pd rdn t vrtn n nntrtn n ld t 19 8 Sthtr xtr nd prr 20 tr nflnn rtn pd 2 Infln f tprtr 2 2 Infln f th nntrtn (r prtl prr f 2 Othr vrbl 2 Chapter 2. Reaction Mechanisms and Elementary Steps 2 2 pr f nt 2 22 tn hn 26 22 fntn 26 222 Expl f hn 2 2 tn ntrdt 2 2 Extd t (r ll 2 22 r rdl 0 2 In 0 24 Adrbd p 31 2 nt dft 31 26 h fft f ntrdt n xtnt nd pd 31 24 tn n nd Snv rprnttn 2 24 Snv dr 2 242 nr n nd ltpnt n 33 2 Chn rtn 4 2 fntn 4 22 h dffrnt tr f hn rtn 35 2 h tp n hn rtn 35 24 Sn f hn rtn 35 2 tn f rll frtn 6 26 Ctlt rtn 37 26 n tl 8 262 trn tl 39 2 Iprtnt fr n rtn hn 4 Chapter 3. Kinetic Properties of Elementary Reactions 4 Sp fntn f n lntr rtn 4 2 tvt nd rt f n lntr tp 44 Knt ntnt f n lntr tp 4 Exprn f rtvt fntn f nntrtn 4 2 t ftr f n lntr rtn 46 4 Oppt lntr rtn 4 Table of Contents vii 3.4.1. Reactivity of two opposite elementary reactions '47 3.4.2. Distance from equilibrium conditions 48 3.4.3. Principle of partial equilibria 49 3.5. Influence of temperature on the reactivities of elementary steps 49 3.5.1. Influence of temperature near the equilibrium 50 3.5.2. Activation energies of opposite elementary reactions and reaction enthalpy 50 3.6. Modeling of a gas phase elementary step 51 3.6.1. Collision theory 52 3.6.2. Theory of activated complex 54 3.7. A particular elementary step: diffusion 58 3.7.1. The diffusion phenomenon 58 3.7.2. Diffusion flux and Fick's first law 58 3.7.3. Diffusion flux in a steady state system 59 3.7.4. Reactivity and diffusion space function 60 3.7.5. Diffusion in solids 62 3.7.6. Interdiffusion of gases 63 3.7.7. Diffusion of a gas in a cylindrical pore 64 3.8. Gases adsorption onto solids 64 3.8.1. Chemisorption equilibrium: Langmuir model 65 3.8.2. Dissociative adsorption and the Langmuir model 66 3.8.3. Chemisorption of gas mixtures in the Langmuir model 68 3.8.4. Chemisorption kinetic in the Langmuir model 70 3.9. Important figures in the kinetic properties of elementary reactions 71 Chapter 4. Kinetic Data Acquisition 73 4.1. Experimental kinetic data of a reaction 73 4.2. Generalities on measuring methods 74 4.3. Chemical methods 74 4.4. Physical methods 75 4.4.1. Methods without separation of components 75 4.4.2. Physical methods with separation of components 84 4.4.3. Study of fast reactions 85 4.5. Researching the influence of various variables 87 4.5.1. Ostwald's isolation method 88 4.5.2. Variables separation 88 Chapter 5. Experimental Laws and Calculation of Kinetic Laws of Homogeneous Systems 91 5.1. Experimental laws in homogeneous kinetics 91 5.1.1. Influence of concentrations 92 viii An Introduction to Chemical Kinetics 5.1.2. Influence of temperature 94 5.2. Relationship between the speed of a reaction and the speeds of its elementary steps 95 5.3. Mathematical formulation of speed from a mechanism and experimental conditions 96 5.3.1. Example of resolution of a mechanism in a closed system 96 5.3.2. Example of resolution of a mechanism in an open system with constant concentrations 98 5.4. Mathematical formulation of a homogeneous reaction with open sequence 99 5.4.1. Mathematical formulation in a closed system 99 5.4.2. Mathematical formulation of a system with constant concentrations 100 5.5. Mathematical formulation of chain reactions 101 5.5.1. Mathematical formulation of a simple homogeneous chain reaction 101 5.5.2. Mathematical formulation of a reaction forming a macromolecule through polymerization 103 Chapter 6. Experimental Data and Calculation of Kinetic Laws of Heterogeneous Reactions 109 6.1. Heterogeneous reactions 109 6.1.1. Distinctive nature of heterogeneous systems 109 6.1.2. Rate of a heterogeneous reaction 110 6.1.3. Different kinetic classes of heterogeneous reactions 110 6.2. Experimental kinetic data of heterogeneous reactions 112 6.2.1. Catalytic reactions 113 6.2.2. Stoichiometric heterogeneous gas—solid reactions 116 6.3. Involvement of diffusion in matter balances 119 6.3.1. Balance in a slice of a volume zone 120 6.3.2. Balance in a 2D zone 122 6.3.3. Application of balances to the elementary steps of a sequence of reactions 123 6.3.4. Application to Fick's second law . ..... .. 124 6.4. Example of mathematical formulation of a heterogeneous catalytic reaction 124 6.5. Example of the mathematical formulation of an evolution process of a phase 127 6.5.1. Balance of intermediates 129 6.5.2. Expressions of the reactivities of elementary chemical steps . 130 6.5.3. Expressions of the concentrations of species at the interfaces. 130 6.5.4. Diffusion equations of the defects 131 Table of Contents ix 6.5.5. Expressions of the variations in sizes of the zones involved in the reaction 132 6.5.6. Evolution law of the rate chosen to characterize the speed 132 Chapter 7. Pseudo- and Quasi-steady State Modes 135 7.1. Pseudo-steady state mode 135 7.1.1. Definition 135 7.1.2. Uniqueness of the reaction speed in pseudo-steady state mode . 136 7.1.3. Linear sequences in pseudo-steady state modes 137 7.1.4. Multipoint sequences in pseudo-steady state mode 140 7.1.5. Experimental research into the pseudo-steady state 141 7.2. Pseudo-steady state sequences with constant volume (or surface) — quasi-steady state 147 7.2.1. Quasi-steady state sequences 147 7.2.2. Linear sequences in quasi-steady state mode 148 7.2.3. Speed of a homogeneous linear sequence in quasi-steady state mode with invariant volume 149 7.2.4. Multipoint sequences in quasi-steady state mode 149 7.3. Pseudo- and quasi-steady state of diffusion 150 7.4. Application to the calculation of speeds in pseudo-steady state or quasi-steady state 151 7.4.1. Principle of the method 151 7.4.2. Example 1: dinitrogen pentoxide decomposition 151 7.4.3. Example 2: hydrogen bromide Synthesis 152 7.4.4. Example 3: polymerization 154 7.4.5. Example 4: application of the pseudo-steady state to a heterogeneous catalytic reaction 156 7.5. Pseudo-steady state and open or closed systems 159 7.5.1. Kinetics law in homogeneous closed systems 159 7.5.2. Kinetics law in heterogeneous closed systems 161 7.5.3. Kinetic laws of open systems with constant concentrations 162 7.6. Conclusion 162 7.7. Important figure in pseudo-steady state 163 Chapter 8. Modes with Rate-determining Steps 165 8.1. Mode with one determining step 166 8.1.1. Definition 166 8.1.2. Concentrations theorem for linear sequences 166 8.1.3. Reactivity of the rate-determining step 170 8.1.4. Rate of reaction 171 x An Introduction to Chemical Kinetics 8.1.5. Calculation of Speed of a linear sequence in pure mode determined by one step 172 8.1.6. Pure modes away from equilibrium for linear sequences 179 8.1.7. Influence of temperature on linear sequences 180 8.1.8. Cyclic sequences 182 8.1.9. Conclusion on modes with a single determining step 183 8.2. Pseudo-steady state mode with two determining steps 185 8.2.1. Definition 185 8.2.2. Mathematical formulation of a mixed pseudo-steady state mode 185 8.2.3. Linear sequences: inverse rate law or the law of slowness 186 8.2.4. Cyclic sequences 188 8.2.5. Law of characteristic times 188 8.3. Generalization to more than two determining steps 189 8.4. Conclusion to the study of modes with one or several rate-determining steps 190 8.5. First order mode changes 190 8.6.
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