Chemical Kinetics 1 Overview Getting Started Techniques Procedure FAQ Full Lab Manual Introduction & Goals Chemistry & Background Key Questions Prelab Problems Safety Procedure In Your Write-up Experiments Index ChemLab Home		Goals In this two-week experiment you will measure the rates of chemical reactions. By observing the progress of a reaction over time, you will determine the rate law, test a possible mechanism, and determine the temperature dependence of the reaction rate constant. In week 1, you will determine the rate law and postulate a rate limiting step for the reaction. In week 2, you will measure the rate constant at different temperatures, to determine the reaction's activation energy. To Learn or Review Reaction Rates Zumdahl, pp. 685-690 Rate Laws Zumdahl, pp. 690-708 Reaction Mechanisms Zumdahl, pp. 708-714 Model for Kinetics Zumdahl, pp. 717-722 Introduction A recent proposal on the organization of chemistry has called for dividing the field into the subdivisions of structure, dynamics, and synthesis. Structure would encompass those aspects of molecular behavior that do not change with time. The shapes, sizes, and relative energies of molecules are examples of the concerns of structural chemistry. Chemical dynamics, on the other hand, emphasizes the understanding of how molecules undergo chemical reactions, and why some reactions are fast and others slow. Finally, synthesis involves the application of both structural and dynamic principles to the problem of preparing new materials or finding new preparative routes to known compounds. Although the lines dividing these areas are not well-defined, the experimental work you have done so far falls more naturally into the structure subdivision than into the dynamics category. Less explicit attention has been devoted to the critical time dimension of molecular behavior. In acid-base titrations, for instance, equilibrium is reached essentially instantaneously at all stages in a titration. Such reactions are analytically useful mainly because they occur rapidly, compared to the time scale of ordinary laboratory manipulations. The study of chemical dynamics can provide penetrating insight into exactly how starting materials in a chemical reaction are converted into the corresponding products. Most chemical reactions do not occur in a single step, but rather involve a series of consecutive elementary events. Taken together, this sequence of chemical events is called the mechanism of the reaction. If one of these steps occurs much more slowly than the others, the rate at which it proceeds will govern the overall rate of formation of the reaction products. Under such conditions, this relatively slow step is called the rate determiningor rate limitingstep. Sophisticated experimental techniques are now available which can probe the dynamics of even very fast reactions, such as that between H3O+ and OH- to form water. Conventional techniques, however, are better suited to studying the rates of reactions which have time scales of minutes to hours. The kinetic experiments to be undertaken in the next two weeks involve reactions which can be conveniently observed over those time intervals.
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