General Chemistry Principles, Patterns, and Applications, 2011

Chemical Kinetics
The gases, liquids, solids, and solutions that you learned to describe quantitatively in , ,, and , respectively, are
systems whose chemical compositions do not change with time. Now we will present a quantitative description of a
far more common situation in which the chemical composition of a system is not constant with time. An example of
such a system is the stratosphere, where chemicals rising from the ground level initiate reactions that lead to
decreases in the concentration of stratospheric ozone—the so-called ozone hole. (For more information about the
ozone hole, see , .) Another example involves the production of polyethylene, in which the properties of the plastic are
determined by the relative speeds of events that occur during the polymerization reaction. (For more information
about the polymerization reaction, see , .) The techniques you are about to learn will enable you to describe the speed
of many such changes and predict how the composition of each system will change in response to changing
conditions.
The Belousov-Zhabotinsky reaction is, a chemical reaction that oscillates in time and space. When a very thin layer of
an acidic solution containing potassium bromate (KBrO3), cerium ammonium nitrate [(NH4)2Ce(NO3)6], malonic acid
(HO2CCH2CO2H), and an indicator is poured into a shallow dish, local fluctuations in the concentration of the
reactants and a complex series of reactions cause striking geometric patterns of concentric circles and spirals to
propagate across the dish.
We begin with a discussion of chemical kinetics, which is the study ofreaction rates, or the changes in the
concentrations of reactants and products with time. As you learn about the factors that affect reaction rates, the
methods chemists use for reporting and calculating those rates, and the clues that reaction rates provide about events
at the molecular level, you will also discover the answers to questions such as the following: How can normally stable
substances such as flour and coal cause devastating explosions? How do archaeologists use isotopic composition to
estimate the ages of ancient artifacts? How do the catalysts used in catalytic converters, some laundry detergents, and
meat tenderizers work?
Summary
Chemical kinetics is the study of reaction rates, the changes in the concentrations of reactants and
products with time.
14.1 Factors That Affect Reaction Rates
L E A R N I N G O B JE C T I V E
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