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
12 - Initial rate experiments and simple empirical rate laws
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
This chapter will introduce you to the analysis of a key class of kinetics experiments, namely initial rate experiments. We will consider only the simplest class of rate laws, those where the rate is proportional to some powers of the concentrations. This is a limited class, but one that comes up surprisingly often in practice. Initial rate experiments are also useful when a reaction has a complex rate law. However, complex rate laws are best understood in the context of a study of reactionmechanisms, so we put off this discussion for now.
Initial rate studies
Rate laws of chemical reactions are often complicated. They can depend on the concentrations of reactants, products, or other chemicals present in the system in almost arbitrary ways. It would be impractical to try to deal at once with all possible complications, so we often try to study reactions under conditions in which we can expect simpler behavior.
Perhaps the most widely used experimental simplification is the method of initial rates, which was briefly mentioned in Section 11.3. In this method, we study the reaction only for a very short time after initiation. During this time, the concentrations change very little so that a number of complications arising from changes in the reaction mixture over time are avoided. For instance, if we start with a mixture containing only reactants, then very little product will accumulate during the reaction and we can neglect the reverse reaction whose rate, according to the law of mass action, depends on the product concentrations.
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- Information
- A Life Scientist's Guide to Physical Chemistry , pp. 234 - 243Publisher: Cambridge University PressPrint publication year: 2012