Reaction rates increasing

Hydrolysis of TEOS in various solvents is such that for a particular system increases directiy with the concentration of H" or H O" in acidic media and with the concentration of OH in basic media. The dominant factor in controlling the hydrolysis rate is pH (21). However, the nature of the acid plays an important role, so that a small addition of HCl induces a 1500-fold increase in whereas acetic acid has Httie effect. Hydrolysis is also temperature-dependent. The reaction rate increases 10-fold when the temperature is varied from 20 to 45°C. Nmr experiments show that varies in different solvents as foUows acetonitrile > methanol > dimethylformamide > dioxane > formamide, where the k in acetonitrile is about 20 times larger than the k in formamide. The nature of the alkoxy groups on the siHcon atom also influences the rate constant. The longer and the bulkier the alkoxide group, the lower the (3). 

Oxygen corrosion of steel doubles for every 35-55°F (20-30°C) rise in temperature, beginning near room temperature. Corrosion is nearly proportional to temperature up to about 180°F (80°C) in systems open to the air. Although reaction rates increase with temperature, dissolved oxygen is driven from solution as temperatures increase. As temperatures approach boiling, corrosion rates fall to very low values, since dissolved-oxygen concentration also decreases as water temperature rises (Fig. 5.4). 

Figure 8.P28 gives the pH-rate profile for conversion of the acid A to the anhydride B in aqueous solution. The reaction shows no sensitivity to buffer concentration. Notice that the reaction rate increases with the size of the alkyl substituent, and, in fact, the derivative with R = = CHj is still more reactive. Propose a mechanism which is... 

Chemical reaction rates increase with an increase in temperature because at a higher temperature, a larger fraction of reactant molecules possesses energy in excess of the reaction energy barrier. Chapter 5 describes the theoretical development of this idea. As noted in Section 5.1, the relationship between the rate constant k of an elementary reaction and the absolute temperature T is the Arrhenius equation ... 

The reaction rate increases when heated to temperatures up to 40°C. The amino derivatives can then be quaternized if desired. The N-methylol derivatives of polyacrylamide can be made cationic by heating with amines, or they can be made anionic by heating with aqueous bisulfite solution under basic conditions. 

While it is generally true to state that reaction rates increase with temperature, such a qualitative statement is not specific enough to be useful and in some circumstances can be incorrect, e.g. at high a values when the deceleratory character of the reaction may be sufficiently great to offset the acceleratory effect of a slow temperature rise. 

In the absence of added mineral acid, the effective chlorinating species was concluded to be chlorine acetate. Like the catalysed chlorination, the rate of chlorination (of toluene) falls rapidly on changing the solvent from anhydrous to 98 % aqueous acetic acid, passes through a shallow minimum and thence to a maximum in 50 % aqueous acid this was thus attributed to a combination of the decrease in concentration of chlorine acetate as water is added and a solvent effect. By correcting for the change in concentration of chlorine acetate in the different media it was shown that the reaction rate increases as the water content of the media increases. 

The amount of catalyst and pH of the reaction determine the extent of pheno-late formation. Phenol-formaldehyde mixtures (F/P = 1.5, 60°C) did not react at pH = 5.5 and reaction rate increased as the pH was increased to about 9.25.55... 

As a result of these branching processes, the chain produces an increasingly larger number of radicals that can take part in even more branching steps. The reaction rate increases rapidly, and an explosion typical of many combustion reactions may occur (Fig. 13.20). 

When 0.52 g of H2 and 0.19 g of 12 are confined to a 750.-mL reaction vessel and heated to 700. K, they react by a second-order process (first order in each reactant), with k = 0.063 L-mol -s 1 in the rate law (for the rate of formation of HI), (a) What is the initial reaction rate (b) By what factor does the reaction rate increase if the concentration of H2 present in the mixture is doubled ... 

A reaction rate increases by a factor of 1000. in the presence of a catalyst at 25°C. The activation energy of the original pathway is 98 kj-mol. What is the activation energy of the new pathway, all other factors being equal In practice, the new pathway also has a different pre-exponential factor. 

Rideout and Breslow first reported [2a] the kinetic data for the accelerating effect of water, for the Diels Alder reactions of cyclopentadiene with methyl vinyl ketone and acrylonitrile and the cycloaddition of anthracene-9-carbinol with N-ethylmaleimide, giving impetus to research in this area (Table 6.1). The reaction in water is 28 to 740 times faster than in the apolar hydrocarbon isooctane. By adding lithium chloride (salting-out agent) the reaction rate increases 2.5 times further, while the presence of guanidinium chloride decreases it. The authors suggested that this exceptional effect of water is the result of a combination of two factors the polarity of the medium and the... 

After the discovery of the remarkable acceleration of some Diels Alder reactions performed in water, a number of polar non-aqueous solvents and their salty solutions were investigated as reaction medium. This revolutionized the concept that the Diels-Alder reaction is quite insensitive to the effect of the medium and emphasized that a careful choice of the solvent is crucial for the success of the reaction. The polarity of the reaction medium is an important variable which also provides some insights into the mechanism of the reaction. If the reaction rate increases by using a polar medium, this means that the transition state probably has polar character, while the absence of a solvent effect is generally related to an uncharged transition state. 

These observations are consistent with the proposed mechanism of the reaction being diffusion controlled in the laminar flow regime. The mass transport is aided by the velocity gradient and thus the reaction rate increases as the Reynolds number is increased. 

Figure k shows the observed pressure and temperature data for Test 2. Initially, the external electric heater controlled the system s temperature and supplied heat to initiate the reaction. Later, as the reaction rate increased, the reaction itself generated heat at a significantly higher rate than the heater imput. 

Suppose this reaction is occurring in a CSTR of fixed volume and throughput. It is desired to find the reaction temperature that maximizes the yield of product B. Suppose Ef > Ef, as is normally the case when the forward reaction is endothermic. Then the forward reaction is favored by increasing temperature. The equilibrium shifts in the desirable direction, and the reaction rate increases. The best temperature is the highest possible temperature and there is no interior optimum. 

The reaction rate increased with temperature. The hydrolysis rate of AG at temperatures lower than 70 °C was very slow. At 80 °C, only complete release of arabinose was achieved, but partially hydrolyzed galactose residue was left. The conversion of AG was 43%. A complete conversion of AG to monomers was achieved at 90 and 100 °C. After the hydrolysis at 100 °C, traces of degradation products such as furfural were observed. For this reason, the temperature for AG hydrolysis shall not exceed 100 °C. 

Fig. 2 shows the effects of the intensity on the reaction rate of TCE. As shown, the TCE reaction rate increases with an increasing UV light intensity and it seems fliat more electron-hole pairs are produced by the UV li t. Thus, more photons can bring forth a greats degradation of the TCE. Obbe and Brown [4] reported that the dependency of the photoreaction rate on the ultraviolet li t intensity followed a power law. The reaction rate on the ultraviolet intensity follows a power law such as ... 

When a reaction proceeds in a single elementary step, its rate law will mirror its stoichiometry. An example is the rate law for O3 reacting with NO. Experiments show that this reaction is first order in each of the starting materials and second order overall NO + 03- NO2 + O2 Experimental rate = i [N0][03 J This rate law is fully consistent with the molecular view of the mechanism shown in Figure 15-7. If the concentration of either O3 or NO is doubled, the number of collisions between starting material molecules doubles too, and so does the rate of reaction. If the concentrations of both starting materials are doubled, the collision rate and the reaction rate increase by a factor of four. 

Polymerizations conducted in nonaqueous media in which the polymer is insoluble also display the characteristics of emulsion polymerization. When either vinyl acetate or methyl methacrylate is polymerized in a poor solvent for the polymer, for example, the rate accelerates as the polymerization progresses. This acceleration, which has been called the gel effect,probably is associated with the precipitation of minute droplets of polymer highly swollen with monomer. These droplets may provide polymerization loci in which a single chain radical may be isolated from all others. A similar heterophase polymerization is observed even in the polymerization of the pure monomer in those cases in which the polymer is insoluble in its own monomer. Vinyl chloride, vinylidene chloride, acrylonitrile, and methacryloni-trile polymerize with precipitation of the polymer in a finely divided dispersion as rapidly as it is formed. The reaction rate increases as these polymer particles are generated. In the case of vinyl chloride ... 

The cementition reaction between zinc oxide powder and aqueous zinc chloride was found to be both rapid and extremely exothermic. Although at least four days equilibration was allowed before examining any of the cements in detail, Sorrell found evidence that reaction was complete within 20 to 30 minutes and occurred without observable development of intermediate phases. He also found that, as the concentration of reactants was increased, so reaction rate increased until, at sufficiently high concentrations, reaction occurred too quickly to allow proper mixing of the reactants. Preheating the zinc oxide at 900 °C for 16 hours was found to slow the reaction down, but only slightly. 

An increase in reaction rate with ethylene partial pressure was observed, but does not follow a first-order law. An averaged formal order of 0.53 was calculated [4]. The reaction rate increases with increasing oxygen partial pressure on OAOR-modified silver with an order of 0.78 with respect to oxygen ]4]. 

GL 16] [R 12] [P 15] On increasing the gas flow rate from 3.2 to 6.6 seem min at a constant liquid flow rate of 75 mg min, the conversion and average reaction rate increase [11] (see also [58]). This is a hint for mass transfer limitations. 

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