Dissolved oxygen first-order rate constant

Under photostationary conditions, the slopes of the linear plots of the consumption of dissolved oxygen are the observed pseudo-first order rate constant of the chemical quenchers, k hs (Criado et al., 2008), and the rate constant for the reactive quenching of 1O2 by GA is calculated with eqn. 12. 

The composition of the reaction mixture in the vessel will be maintained at a constant low conversion by continuous withdrawal of the product stream and a steady inflow of fresh o-xylene. Under these conditions the reaction rate is approximately independent of the o-xylene concentration and is pseudo first-order with respect to the dissolved oxygen concentration C0. 

In activity tests, sections of the Zn composite were used as agitation paddles in a batch reactor and compared to granular zinc, which was loaded into a similar vessel with an inert agitator (Fig. 23). The reactors were charged with 1 L of water and sparged with nitrogen to remove dissolved oxygen. TCE was then added to a concentration of 1(X)0 ppm. A chloride selective electrode was used to monitor chloride ion formation as a function of reaction time. First order kinetics were assumed, and rate constants were calculated per mass of Zn. 

Some information regarding the Ea for ascorbic acid in food systems can be found in the literature. Kirk et al. (17) determined that the vitamin C destruction in a model dehydrated food system could be described by the first-order function. Rates of destruction were influenced by dw, moisture, and temperature of storage. Activation energies for TAA destruction at above 0.24 were approximately 18 kcal/mol, similar to those reported for RAA by Lee and Labuza (78). Lower EaS were reported at a s less than 0.24, suggesting a diflFerent mechanism for ascorbic acid destruction, perhaps by an anaerobic pathway. Rate constants were also influenced by the packaging used for the model food system, which may be attributed to the amount of dissolved oxygen present. 

These studies indicated that the photoproduction rates in solutions of varying composition were approximately proportional to the dissolved organic carbon (DOC) content. Assuming that the lifetime of the solvated electron in air-saturated water is 0.2 ps and that halocarbon concentrations are much lower than that of oxygen (and thus have little effect on the electron lifetime), the photoproduction rate observed in the Greifensee (DOC = 4 mg of C/L) corresponded to estimated near-surface pseudo-first-order photoreduction rate constants of about lOVh for several halocarbons known to be present in natural waters (Table V). These estimates were derived by using previously measured rate constants for reaction of solvated electrons with the halocarbons (48). 

The Sotolon formation was studied as a function of temperature, pH, SO2 and oxygen concentration. Temperature and to a lesser extent, dissolved oxygen were tlie most important parameters influencing the rate of Sotolon formation. A first order model was applied and the Arrhenius equation described well the temperature dependence of the reaction rate constant. Therefore, oxygen levels during aging have a major impact on age perception" in Colheita and Vintage Port wine. 

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