Formation of Ozone from Oxygen

Historically, the photochemistry of oxygen and ozone has been of considerable interest because of the importance of oxygen and ozone in the atmosphere. In 1881 Hartley (39) postulated that ozone was a normal constituent of the upper atmosphere and that absorption of solar radiation by ozone could account for the limitation of the solar spectrum at about 3000 A. These speculations were not definitely corroborated until 1913 by Fabry and Buisson (26). The formation of ozone from oxygen in ultraviolet light in the region 1400-1900 A. was first reported by Lenard (53) in 1900 and afterwards confirmed by Goldstein (34) in 1903. 

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In 1899, the Curies first reported the coloration of glass and porcelain and the formation of ozone from oxygen by radioactive radiation. Giesel (1900) noted that the coloration of alkali halides under these radiations was similar to the effect of cathode rays he also observed the decomposition of water. R Curie and Debierne (1901) observed continuous evolution of hydrogen and oxygen... 

The formation of ozone from oxygen absorbs heat ozone therefore should be the more stable the higher the temperature now it is sufficient to heat to 200 ozonized oxygen in order to have every trace of ozone disappear. 

Reaction is nonspontaneous at all temperatures AH > 0, AS < 0. Both contributions oppose the spontaneity of the reaction. AH is positive and AS is negative, so —TAS is positive thus, AG is always positive. The formation of ozone from oxygen is not spontaneous at any temperature ... 

The following processes were all discussed in Chapter 18, Chemistry of the Environment Estimate whether the entropy of the system increases or decreases during each process (a) photodissociation of 02(g), (b) formation of ozone from oxygen molecules and oxygen atoms, (c) diffusion of CFCs into the stratosphere, (d) desalination of water by reverse osmosis. 

These radicals, which are chemically very reactive, have only a brief existence in the laboratory. But in air and at high altitudes where molecules are far apart and collissions are infrequent, some of the radicals persist for appreciable times and serve as intermediaries in reactions that would otherwise be extremely slow. For example, the formation of ozone from oxygen can be written... 

As an example, consider the formation of ozone from oxygen ... 

Reaction (12-9) shows the photochemical dissodation of NO2. Reaction (12-10) shows the formation of ozone from the combination of O and molecular O2 where M is any third-body molecule (principally N2 and O2 in the atmosphere). Reaction (12-11) shows the oxidation of NO by O3 to form NO2 and molecular oxygen. These three reactions represent a cyclic pathway (Fig. 12-4) driven by photons represented by hv. Throughout the daytime period, the flux of solar radiation changes with the movement of the sun. However, over short time periods (—10 min) the flux may be considered constant, in which case the rate of reaction (12-9) may be expressed as... 

In the following reaction sequence for the catalytic formation of ozone from molecular oxygen, which chemical compound is the catalyst nitrogen monoxide or nitrogen dioxide ... 

Chemical radicals—such as hydroxyl, peroxyhydroxyl, and various alkyl and aryl species—have either been observed in laboratory studies or have been postulated as photochemical reaction intermediates. Atmospheric photochemical reactions also result in the formation of finely divided suspended particles (secondary aerosols), which create atmospheric haze. Their chemical content is enriched with sulfates (from sulfur dioxide), nitrates (from nitrogen dioxide, nitric oxide, and peroxyacylnitrates), ammonium (from ammonia), chloride (from sea salt), water, and oxygenated, sulfiirated, and nitrated organic compounds (from chemical combination of ozone and oxygen with hydrocarbon, sulfur oxide, and nitrogen oxide fragments). ... 

Light absorption by oxygen has been observed from the near infrared to the far ultraviolet. Absorption above about 2500 A. is of some interest in connection with proposed photochemical reactions of oxygen with some other molecules. For the formation of ozone, however, the middle and short ultraviolet region is of primary interest. 

The effects of various added gases on the rate of formation of ozone in a flow system have been studied at 1849 A. with light from a mercury-rare gas low pressure discharge (92). In a 30-mm. diameter cylindrical quartz reaction vessel at a flow rate of 2.0 l./min. at 1-atm. total pressure and 0.25-atm. oxygen pressure, the relative rates of ozone formation were ... 

An important example of an association reaction is the formation of ozone in the stratosphere from atomic and molecular oxygen O + O2 + M —> O3 + M. At low pressures, a third-order rate law is found with rate constants given in the table below for M = N2 [J. Phys. Chem. Ref. Data 26, 1329 (1997)]. 

Second stage (aldehyde) oxidation under the conditions of ozone and oxygen rates used is considered to require only about one-half of the time required for double bond cleavage. Thus, polymer oxidation is considered complete in about 45 minutes in the experiments plotted in Figures 3 and 4. Total acid formation after —45 minutes—i.e., the part with the flattest slope—is thought to arise from ozonization of pyridine or solvent and will be considered as such in further discussions. 

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