Book contents
- Frontmatter
- Contents
- Preface
- 1 Orientation: what is physical chemistry about?
- Part One Quantum mechanics and spectroscopy
- Part Two Thermodynamics
- Part Three Kinetics
- 11 Basics of chemical kinetics
- 12 Initial rate experiments and simple empirical rate laws
- 13 Integrated rate laws
- 14 Complex reactions
- 15 Enzyme kinetics
- 16 Techniques for studying fast reactions
- 17 Factors that affect the rate constant
- 18 Diffusion and reactions in solution
- Appendix A Standard thermodynamic properties at 298.15 K and 1 bar
- Appendix B Standard reduction potentials at 298.15 K and 1 bar
- Appendix C Physical properties of water
- Appendix D The SI system of units
- Appendix E Universal constants and conversion factors
- Appendix F Periodic table of the elements, with molar masses
- Appendix G Selected isotopic masses and abundances
- Appendix H Properties of exponentials and logarithmic functions
- Appendix I Review of integral calculus
- Appendix J End-of-term review problems
- Appendix K Answers to exercises
- Index
14 - Complex reactions
from Part Three - Kinetics
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Preface
- 1 Orientation: what is physical chemistry about?
- Part One Quantum mechanics and spectroscopy
- Part Two Thermodynamics
- Part Three Kinetics
- 11 Basics of chemical kinetics
- 12 Initial rate experiments and simple empirical rate laws
- 13 Integrated rate laws
- 14 Complex reactions
- 15 Enzyme kinetics
- 16 Techniques for studying fast reactions
- 17 Factors that affect the rate constant
- 18 Diffusion and reactions in solution
- Appendix A Standard thermodynamic properties at 298.15 K and 1 bar
- Appendix B Standard reduction potentials at 298.15 K and 1 bar
- Appendix C Physical properties of water
- Appendix D The SI system of units
- Appendix E Universal constants and conversion factors
- Appendix F Periodic table of the elements, with molar masses
- Appendix G Selected isotopic masses and abundances
- Appendix H Properties of exponentials and logarithmic functions
- Appendix I Review of integral calculus
- Appendix J End-of-term review problems
- Appendix K Answers to exercises
- Index
Summary
I have mentioned several times in the past few chapters that complex reactions can have either simple or complex rate laws. We will now see how complex reactions can give rise to complex rate laws, but also how these rate laws often simplify to simple forms.
You may notice as you read this chapter that it seems to focus a lot on gas-phase chemistry, and that there are few biological examples and problems. This is a deliberate choice. First of all, gas-phase chemistry is of interest to biologists since the atmosphere ties us all together. My second reason for focusing on gas-phase chemistry here has to do with pedagogy: examples of complex mechanisms deriving from gas-phase chemistry are often simpler than those arising in biochemistry.We will get a good grounding in the basic methods for treating complex mechanisms in this chapter before moving on to enzyme kinetics in the next chapter.
Two-step mechanisms
In order to get our feet wet with complex reactions, we will try to resolve a puzzle: on the surface, unimolecular gas-phase reactions, i.e. reactions with the stoichiometry A → product(s), should be the simplest reactions around. However, these reactions always have complex rate laws: at low pressures, they display second-order kinetics, while at high pressures, they follow first-order kinetics with respect to the reactant. (At intermediate pressures, the rate can't be described by either a first- or a second-order rate law.)
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- Chapter
- Information
- A Life Scientist's Guide to Physical Chemistry , pp. 274 - 286Publisher: Cambridge University PressPrint publication year: 2012