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Introduction to Reaction Kinetics


Table of Contents


Kinetics, the study of the rates of chemical reactions, has a profound impact on our daily lives. Even though some reactions are thermodynamically favorable, such as the conversion of diamonds into graphite, they do not occur at a measurable rate at room temperature. Other reactions, like the explosive reaction between vinegar and baking soda, occur almost instantaneously. Imagine a world where all thermodynamically favored processes occurred at the same rate--life could not exist under such circumstances because biological processes rely on the kinetic stability of many unstable compounds. Kinetics answers questions about rate, how fast reactions go, and mechanisms, the paths molecules take in going from reactants to products.

To describe the rate of a reaction, we will derive the rate law for a chemical reaction and discuss the factors affecting rate. Additionally, we will describe the experimental techniques, such as the method of initial rates and fitting data to plots based on the integrated rate law, used to determine the rate law for an unknown reaction.

In our discussion on mechanisms, we will discuss how to determine the path a reaction takes by analyzing and predicting the series of elementary steps that comprise a mechanism. By comparing the rate law for a proposed mechanism and other mechanistic predictions to experimental data, we can test the validity of a mechanism. Mechanisms can never be proven exactly, but we can rule out mechanisms that disagree with experimental observations. We will use reaction coordinate diagrams to understand and to visualize reaction mechanisms, thermodynamics, and activation energies. Catalysts and intermediates can be important factors in reaction mechanisms, and they provide interesting examples of mechanism problems.

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