Reaction determining step

Si(OC2H5). In the two-step process of hydrolysis of the silane to the silanol species and the condensation (silanols to siloxane), the reaction-determining step is the rate of hydrolysis [54]. However, for polyfunctional silanes, hydrolysis and condensation overlap. Under defined reaction conditions, the reaction between the surface hydroxyl groups of the sihca and the silane compound follows a distinct stochiometry, which can be expressed by the number of surface hydroxyl groups that react with the organosilane. For monofunctional silanes this ratio is unity. 

MASS TRANSPORT COEFFIECINT 4.1 Reaction determining step... 

The reaction determining step in Scheme 21 is the transformation of the radical derived from the o -complex. It can undergo dissociation of either C-H (Ac hG°) or C-Nu bond (Ac nuG°) to give radical-anion of the Sn product or the starting... 

If the first step would limit the reaction rate, the cathodic Tafel coefficient would be identical to that of the Volmer-Heyrovsky mechanism (the anodic Tafel coefficient would be different though). On the other hand, if the second step is rate determining the cathodic Tafel slope differs. The rate of the reaction determining step, Vn, is given by... 

The measurement of rates and activation energy of chemisorption is very important for catalytic mechanism and its applied research. It is clear that when the adsorption is the reaction determining step of catalytic reaction, the rate of adsorption process will determine the rate of the reaction and activity of catalysts. Therefore, activation energy and heat of adsorption can reflect the nature of the active site and distinguish the t3rpe of active site imder certain conditions. 

CO -I- M CO — M equilibrium constant Kco V2O2 -I- M -o- O — M equilibrium constant Ko Surface reaction (determining step)... 

The treatment may be made more detailed by supposing that the rate-determining step is actually from species O in the OHP (at potential relative to the solution) to species R similarly located. The effect is to make fi dependent on the value of 2 and hence on any changes in the electrical double layer. This type of analysis has permitted some detailed interpretations to be made of kinetic schemes for electrode reactions and also connects that subject to the general one of this chapter. 

The measurement of a from the experimental slope of the Tafel equation may help to decide between rate-determining steps in an electrode process. Thus in the reduction water to evolve H2 gas, if the slow step is the reaction of with the metal M to form surface hydrogen atoms, M—H, a is expected to be about If, on the other hand, the slow step is the surface combination of two hydrogen atoms to form H2, a second-order process, then a should be 2 (see Ref. 150). 

B. Reaction within the Adsorbed Film as the Rate-Determining Step... 

The above equations can apply when the rate-determining step is first order even though the complete reaction mechanism is complicated. Thus for the reac-... 

It may seem, at first sight, paradoxical that a competition reaction carried out under conditions in which the measured rate is independent of the concentration of the aromatic can tell us about the relative reactivities of two aromatics. Obviously, the measured rate has nothing to do with the rate of the product-determining step, and what is important in determining relative reactivities is the ratio of the values of ( 3.2.4) for two compounds. The criteria to be met for a correct application of the competitive method are well understood. ... 

With the potential energies shown on a common scale we see that the transition state for formation of (CH3)3C is the highest energy point on the diagram A reaction can proceed no faster than its slowest step which is referred to as the rate determining step In the reaction of tert butyl alcohol with hydrogen chloride formation of the... 

Assuming that the rate determining step in the reaction of cyclohexanol with hydrogen bro mide to give cyclohexyl bromide is unimolecular write an equation for this step Use curved arrows to show the flow of electrons... 

Like the reaction of tert butyl alcohol with hydrogen chloride step 2 m which tert butyloxonium ion dissociates to (CH3)3C and water is rate determining Because the rate determining step is ummolecular the overall dehydration process is referred to as a ummolecular elimination and given the symbol El... 

Because the rate determining step involves two molecules—the alkyloxonium ion and water—the overall reaction is classified as a bimolecular elimination and given the sym bol E2... 

Both steps m this general mechanism are based on precedent It is called elec trophilic addition because the reaction is triggered by the attack of an acid acting as an electrophile on the rr electrons of the double bond Using the two rr electrons to form a bond to an electrophile generates a carbocation as a reactive intermediate normally this IS the rate determining step... 

Table 6 3 shows that the effect of substituents on the rate of addition of bromine to alkenes is substantial and consistent with a rate determining step m which electrons flow from the alkene to the halogen Alkyl groups on the carbon-carbon double bond release electrons stabilize the transition state for bromonium ion formation and increase the reaction rate... 

The reaction occurs in two stages Only the first stage involves nucleophilic substitution It IS the rate determining step... 

The Stvfl mechanism is an ionization mechanism The nucleophile does not participate until after the rate determining step has taken place Thus the effects of nucleophile and alkyl halide structure are expected to be different from those observed for reactions pro ceedmg by the 8 2 pathway How the structure of the alkyl halide affects the rate of Stvfl reactions is the topic of the next section... 

Overall the reaction exhibits second order kinetics Both the ester and the base are involved m the rate determining step or m a rapid step that precedes it... 

Since the rate of a chemical reaction only depends on the slowest, or rate-determining step, and any preceding steps, species B will not show up in the rate law. 

Until now we have been discussing the kinetics of catalyzed reactions. Losses due to volatility and side reactions also raise questions as to the validity of assuming a constant concentration of catalyst. Of course, one way of avoiding this issue is to omit an outside catalyst reactions involving carboxylic acids can be catalyzed by these compounds themselves. Experiments conducted under these conditions are informative in their own right and not merely as means of eliminating errors in the catalyzed case. As noted in connection with the discussion of reaction (5.G), the intermediate is stabilized by coordination with a proton from the catalyst. In the case of autoprotolysis by the carboxylic acid reactant, the rate-determining step is probably the slow reaction of intermediate [1] ... 

An important consequence of the isotope-dependence of Dq is that, if a chemical reaction involves bond dissociation in a rate-determining step, the rate of reaction is decreased by substitution of a heavier isotope at either end of the bond. Because of the relatively large effect on Dq, substitution of for H is particularly effective in reducing the reaction rate. 

In the normal process ( ), step (J) occurs very rapidly and step (/) is the rate-determining step, whereas in the inhibition process (B), step (3) occurs very slowly, generally over a matter of days, so that it is rate determining. Thus it has been demonstrated with AChE that insecticides, eg, tetraethyl pyrophosphate and mevinphos, engage in first-order reactions with the enzyme the inhibited enzyme is a relatively stable phosphorylated compound containing one mole of phosphoms per mole of enzyme and as a result of the reaction, an equimolar quantity of alcohoHc or acidic product HX is hberated. 

The mechanism of the synthesis reaction remains unclear. Both a molecular mechanism and an atomic mechanism have been proposed. Strong support has been gathered for the atomic mechanism through measurements of adsorbed nitrogen atom concentrations on the surface of model working catalysts where dissociative N2 chemisorption is the rate-determining step (17). The likely mechanism, where (ad) indicates surface-adsorbed species, is as follows ... 

In this reaction sequence, equation 47, the formation of the complex ion, Zn(OH)3, is the rate determining step. Once the solubiUty of 2incate, Zn(OH), is exceeded, 2inc hydroxide [20427-58-17, Zn(OH)2, precipitates. The crystal form that falls out of solution depends on the concentration of the alkah. 

For most color photographic systems, development is the rate determining step, and within that step the formation of semiquinone is the slow process (37). The fate of the highly reactive QDI is deterrnined by the relative rates of a number of competing processes (38). The desired outcome is reaction with ionized coupler to produce dye (eq. 3). Typically, the second-order rate constant for this process with ionized coupler is about 10 to 10 ... 

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