lecture_12_2009_1

lecture_12_2009_1 - 62 Chemical Kinetics So far our...

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62 Chemical Kinetics So far, our discussion of chemistry has been concerned with the properties of initial and final states. Calculating equilibrium constants, for example, requires us to know information about the difference in energies of the reactants and products. Chemical kinetics is the first example of a topic in which all of the states that connect reactants and products play a role in determining the behavior of the system. The diagram indicates the fact that all of the states connecting the reactants and products are important in determining reaction rates. Atmospheric Kinetics One of the most important species in the stratosphere is ozone, O 3 , one of the allotropes of oxygen. The formation of ozone begins with the production of oxygen atoms
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63 UV radiation in the stratosphere photodissociates O 2 and makes oxygen atoms: O 2 + light O + O O + O 2 O 3 Remember that formation of a chemical bond is exothermic . The formation of ozone is exothermic enough that the stratosphere actually warms up relative to the troposphere. The diagram above indicates that the ozone layer peaks in density at about 20 km and the concentration of O 3 molecules is about 5 × 10 12 molecules per cm 3 You could even calculate the partial pressure ozone with the ideal gas law if you were so inclined. The concentration of O 3 is maintained at constant levels because The formation rate is determined by O + O 2 O 3 The primary rate of destruction is absorption of UV radiation: O 3 O 2 + O We refer to such a condition as a steady state. This particular steady state condition is especially important in protecting us from harmful UV rays that have been correlated with skin cancer. In the early 1970’s, a proposal to build a fleet of Concorde-style supersonic aircraft was made.
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lecture_12_2009_1 - 62 Chemical Kinetics So far our...

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