Introduction
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.
