Oxygen elementary

Oxygen enters water via diffusion from the atmosphere and it is generated by photosynthetic activity of aqueous plants. It is consumed during aerobic decomposition of organic substances, oxidation of some inorganic compounds and respiration of the organisms present. 

In clean surface waters the concentration of dissolved oxygen is about 85-95% of saturation and varies throughout the day. These diurnal variations depend on the intensity of photosynthesis and changes in the temperatures. In the case of intensive photosynthetic assimilation of green organisms or in turbulent stretches in streams, water can easily become oversaturated by oxygen. At 15°C water is saturated by oxygen at a concentration of about 10 mg 1 .  

As opposed to surface waters, groundwaters are poor in dissolved oxygen but after springing at the surface they are promptly saturated. The presence or absence of dissolved oxygen determines whether aerobic or anaerobic processes will take place in water. It is essential in order to ensure 

It follows that the content of dissolved oxygen is an important indicator of the quality of streams, as one of the first indications of surface water pollution by organic substances is a decrease in the oxygen content downstream from the source of poUution. Oxygen in water is of vital importance for fish, a concentration of 3-4 mg 1 is usually considered to be the lower limit, but this depends on the sensitivity of fish. The salmon-like fish require a concentration of approximately 6 mg 

Oxygen in water is important when evaluating aggressivity of water towards metals (so-called oxygen corrosion), and it is an important index for checking the operation of biological wastewater treatment plants. 

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S.D. Razumovskii, Kislorod - Elementamye Formy i Svoistva (Oxygen - Elementary Forms and Properties), Moscow Khimya, 1979, 314 p. 

S.D. Razumovski, Oxygen. Elementary Forms and Properties, Khimiya Publ., Moscow, 1979 (in Russian)... 

Arden, M., Oxygen Elementary Forms and H2O2, W. A. Benjamin Publ., New York, 1965. 

Ardon, M. (1965) Oxygen. Elementary forms and hydrogen peroxide. W. A. Benjamin, New... 

Ardon M (1965) Oxygen elementary forms and hydrogen peroxide. Benjamin Cummings, San Francisco... 

Elementary oxygen, like NO and NO is paramagnetic (Figure 7.3, p. 173). Experimental evidence suggests that the 02 molecule contains two unpaired electrons and a double bond. 

In semi-cristalline polymers, rate-enhancement under stress has been frequently observed, e.g. in UV-photooxidation of Kapron, natural silk [80], polycaprolactam and polyethylene terephthalate [81]. Quantitative interpretation is, however, difficult in these systems although the overall rate is determined by the level of applied stress, other stress-dependent factors like the rate of oxygen diffusion or change in polymer morphology could occur concurrently and supersede the elementary molecular steps [82, 83], Similar experiments in the fluid state showed unequivocally that flow-induced stresses can accelerate several types of reactions, the best studied being the hydrolysis of DNA [84] and of polyacrylamide [85]. In these examples, hydrolysis involves breaking of the ester O —PO and the amide N —CO bonds. The tensile stress stretches the chain, and therefore, facilitates the... 

The extent to which such reactions take place in parallel with the dominant reaction (4.1) is, in general, difficult to quantify as the overall reaction (4.3a) may consist of the elementary step (4.1) followed by reaction between adsorbed CO and adsorbed oxygen on the metal surface ... 

Transient computations of methane, ethane, and propane gas-jet diffusion flames in Ig and Oy have been performed using the numerical code developed by Katta [30,46], with a detailed reaction mechanism [47,48] (33 species and 112 elementary steps) for these fuels and a simple radiation heat-loss model [49], for the high fuel-flow condition. The results for methane and ethane can be obtained from earlier studies [44,45]. For propane. Figure 8.1.5 shows the calculated flame structure in Ig and Og. The variables on the right half include, velocity vectors (v), isotherms (T), total heat-release rate ( j), and the local equivalence ratio (( locai) while on the left half the total molar flux vectors of atomic hydrogen (M ), oxygen mole fraction oxygen consumption rate... 

Thus, the elementary cellular structure could be regarded as an intrinsic characteristic of fhe detonation in a mixture at given initial composition, temperature, and pressure. The dimension of X is of fhe order of magnitude of millimeters or less for gaseous mixfures with oxygen, but several centimeters for less sensitive mixtures (even larger, for methane/air af afmospheric pressure). It decreases when the initial pressure increases. Its variation with the initial temperature is more complicated and depends on the value of fhe reduced activation energy of fhe chemical reactions. The value of... 

Step (3), the recombination of adsorbed oxygen and adsorbed CO to give adsorbed CO2, is assumed to be the rate-limiting step. We could describe step (2) in more detail, as the adsorption of O2 proceeds via a molecular precursor, O2, which subsequently dissociates. However, for simplicity, we neglect this elementary step, leaving it to the reader to determine the consequences of taking it into account. 

The mechanism is thought to involve dissociation of hydrogen, which reacts with molecularly adsorbed CO2 to form formate adsorbed on the surface. The adsorbed formate is then further hydrogenated into adsorbed di-oxo-methylene, methoxy, and finally methanol, which then desorbs. The reaction is carried out under conditions where the surface is predominately empty and the oxygen generated by the process is quickly removed as water. Only the forward rate is considered and the process is assumed to go through the following elementary steps ... 

Basic physical properties of sulfur, selenium, and tellurium are indicated in Table 1.3. Downward the sulfur sub-group, the metallic character increases from sulfur to polonium, so that whereas there exist various non-metallic allotropic states of elementary sulfur, only one allotropic form of selenium is (semi)metallic, and the (semi)metallic form of tellurium is the most common for this element. Polonium is a typical metal. Physically, this trend is reflected in the electrical properties of the elements oxygen and sulfur are insulators, selenium and tellurium behave as semiconductors, and polonium is a typical metallic conductor. The temperature coefficient of resistivity for S, Se, and Te is negative, which is usually considered... 

The detailed mechanism of forming O2 from water involves a number of elementary reaction steps, so that photoinduced interfacial coordination reactions are needed that may induce water species to form metal complexes, which are gradually oxidized and may, thereby, liberate oxygen. This may be done by introducing... 

The reaction between hydrogen and oxygen leads to the formation of water. This reaction has extended explosive regimes with respect to the p,T,c-parameters. A mechanistic analysis of the elementary reactions is available and the explosion mechanisms are imderstood in detail. Accordingly, this reaction serves well as a model for other dangerous processes in the explosive regime such as many oxidations with pure oxygen. 

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