Chemical kinetics ozone depletion

Thus we see that environmental modeling involves solving transient mass-balance equations with appropriate flow patterns and kinetics to predict the concentrations of various species versus time for specific emission patterns. The reaction chemistry and flow patterns of these systems are sufficiently complex that we must use approximate methods and use several models to try to bound the possible range of observed responses. For example, the chemical reactions consist of many homogeneous and catalytic reactions, photoassisted reactions, and adsorption and desorption on surfaces of hquids and sohds. Is global warming real [Minnesotans hope so.] How much of smog and ozone depletion are manmade [There is considerable debate on this issue.]... 

Chemical kinetics is a subject of crucial environmental and economic importance. In the upper atmosphere, for example, maintenance or depletion of the ozone layer, which protects us from the sun s harmful ultraviolet radiation, depends on the relative rates of reactions that produce and destroy O3 molecules. In the chemical industry, the profitability of the process for the synthesis of ammonia, which is used as a fertilizer, depends on the rate at which gaseous N2 and H2 can be converted to NH3. 

In recent years, it has become possible to extrapolate accurately using detailed chemical kinetic models to predict quantitatively the behavior of some rather complicated chemical systems. The most famous examples of this success are the detailed atmospheric chemistry models whose predictions underlie the Montreal Protocol on ozone-depleting chemicals. However, these atmospheric chemistry models were developed through a huge international effort over several decades, based heavily on a large number of laboratory experiments. Much more rapid and efficient methods of model development are required for detailed predictive chemical kinetics to become a practical everyday design tool for chemical engineering. 

The area of chemistry concerned with the speeds, or rates, of reactions is chemical kinetics. Chemical kinetics relates to how quickly a medicine works in the body, to whether the processes that form and deplete ozone in the atmosphere are in balance, and to such industrial challenges as the development of new catalysts, materials that speed up reactions. 

The area of chemistry that is concerned with the speeds, or rates, of reactions is called chemical kinetics. Chemical kinetics is a subject of broad importance. It relates, for example, to how quickly a medicine is able to work, to whether the formation and depletion of ozone in the upper atmosphere are in balance, and to industrial problems such as the development of catalysts to synthesize new materials. Our goal in this chapter is not only to rmderstand how to determine the rates at which reactions occur, but also to consider the factors that control these rates. For example, what factors determine how rapidly food spoils How does one design a fast-setting material for dental fillings What determines the rate at which steel rusts What controls the rate at which fuel bums in an automobile engine Although we won t address these specific questions directly, we will see that the rates of all chemical reactions are subject to the same basic principles. 

Kinetic- information is acquired lor two different purposes. Hirst, data are needed lor specific modeling applications that extend beyond chemical theory. These arc essential ill the design of practical industrial processes and are also used io interpret natural phenomena such as Ihe observed depletion of stratospheric ozone. Compilations of measured rate constants are published in the United Stales by the National Institute of Standards and Technology (NISTt. Second, kinetic measurements are undertaken to elucidate basic mechanisms of chemical change, simply to understand the physical world The ultimate goal is control of reactions, but the immediate significance lies in the patients of kinetic behavior and the interpretation in terms of microscopic models. 

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