Initial rates of formation

Noncatalytic Reactions Chemical kinetic methods are not as common for the quantitative analysis of analytes in noncatalytic reactions. Because they lack the enhancement of reaction rate obtained when using a catalyst, noncatalytic methods generally are not used for the determination of analytes at low concentrations. Noncatalytic methods for analyzing inorganic analytes are usually based on a com-plexation reaction. One example was outlined in Example 13.4, in which the concentration of aluminum in serum was determined by the initial rate of formation of its complex with 2-hydroxy-1-naphthaldehyde p-methoxybenzoyl-hydrazone. ° The greatest number of noncatalytic methods, however, are for the quantitative analysis of organic analytes. For example, the insecticide methyl parathion has been determined by measuring its rate of hydrolysis in alkaline solutions. 

These definitions are valid only when the concentration of the enzyme is very small compared with that of the substrate. Moreover, they apply only to the initial rate of formation of products in other words, the rate of formation of the first few percent of the product, before the substrate has been depleted and products that can interfere with the catalytic reaction have accumulated. 

Actually one observes (Fig. 4) the formation of acetone and isopropanol, with only traces of isobutyric acid (reaction (9), both products being formed in amounts exceeding 80 % of the amount of DiPK decomposed as indicated by the initial rate of formation). 

Initial rates of formation of C for various initial concentrations of A and B at 400°C are as follows ... 

The initial rate of formation of H2S from hydrogen and sulfur was measured with the results tabulated. In all experiments the closed reaction vessel contained the same initial weights of sulfur and hydrogen. The rate is g H2S/(1iter) (s). Find the activation energy. 

We then use Cleland s procedure to write the expression for the initial rate of formation of labeled P from A. 

A 2-L Pyrex glass flask was filled with a gaseous mixture of xenon (350 ml) and fluorine (374 ml). The total pressure in the flask was 724Torr at 25C. The flask was kept for 3 weeks at rt and exposed to daylight. The formation of fine crystals was noticed on the second day of standing. The initial rate of formation of XeF2 was about 35 mg per day. The total amount of product obtained during 3 weeks varied yield 0.5 to 0.75 g (19-28%). 

Many assays for tyrosinase activity have been developed. Procedures in the literature include use of the oxygen electrode, oxidation of tyrosine followed at 280 nm, and oxidation of dopa followed at 475 nm. The most convenient assay involves following the tyrosinase-catalyzed oxidation of dopa by monitoring the initial rate of formation of dopachrome at 475 nm (Figure E5.8). 

Effect of platinum content. Since a beneficial role of platinum deposited on titania had been reported for the photocatalytic oxidation of some organic compounds (refs 6, 7), several catalysts, from 0.5 to 10 wt % Pt with a constant particle size, were prepared and studied. The variations of the initial rate of formation of cyclohexanone as a function of Pt contents are shown in Fig. 2. There is not only no beneficial effect of Pt as mentioned in refs.(6, 7) but a... 

Fig. 11 shows the theoretical curve for the thermal reaction of the formation of nitric oxide in the combustion products at 2435°K. The equilibrium amount of nitric oxide at this temperature is equal to 0.74%, the initial rate of formation of nitric oxide is 25 volume percent per second. As can be seen from the figure, the observed rate at first coincides closely withj the computed value. Then a lag sets in which is explained naturally by the fall... 

Enzyme kinetics usually are studied by mixing the enzyme and substrates and measuring the initial rate of formation of product or the disappearance of a reactant. Special techniques are necessary to measure very fast reactions. It is common to measure the rate as a function of substrate concentration, pH, and temperature. 

Experiment Initial [NO] Initial [Oz] Initial Rate of Formation of NOz (M/s)... 

Experiment Temperature (K) Initial [A] Initial [B] Initial Rate of Formation of C... 

Initial Rates of Formation of Products (Heicklen and Johnston67)... 

The initial rate of formation of the radical species was temperature dependent. The Arrhenius equation reasonably describes the temperature dependence of the specific rate constants over the temperature range 77°-121° K. The calculated specific rate constants are plotted as a function of temperature in Figure 6 the solid line is the least-squares line through the experimental points. Thus, in the temperature range 77°-121° K., the rate of formation of the paramagnetic entity can be ex-... 

Yang (1991) and Wang et al. (1986) found in a microreactor that the initial rate of formation of (CO + COz) was zero it then climbed to a maximum and decreased gradually according to an exponential function, as shown in Fig. 6. They proposed the formation of an intermediate compound (Cj,Ox) of carbon oxidation and suggested the following mechanism ... 

Rj, is the initial rate of formation of copper protoporphyrin ester in the presence of 5% hexadecyltrimethylammonium bromide. 

The results of an experiment are shown in Figure 10.6. The formation of GMP and IMP from guanine and hypoxanthine, respectively, can be followed. With this method it was possible to track the initial rates of formation of IMP and GMP separately, the initial rates of both determined simultaneously, and the rate of PRibPP utilization with a fixed ratio of hypoxanthine and guanine. 

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