Second step is rate limiting

For a number of inorganic reductants, the second step is rate-limiting and... 

Addition of primary amines to carbonyl groups has been the subject of extensive study, notably by Jencks and co-workers.91 The most striking feature of these reactions is the characteristic maximum in the graph of reaction rate as a function of pH.92 Figure 8.10 illustrates the observations for the reaction of hydroxylamine with acetone. It is also found that the sensitivity of rate to acid catalysis,93 and to substituent effects,94 is different on either side of the maximum in the pH-rate curve. These phenomena may be understood in terms of the two-step nature of the reaction. In acetal formation, we saw in Section 8.3 that the second step is rate-limiting in the overall process, and it is relatively easy to study the two steps separately here, the rates of the two steps are much more closely balanced, so that one or the other is rate-determining depending on the pH. 

Eq. (61). If steady-state conditions are met3 and the second step is rate limiting, Eq. (61) leads to the kinetic law represented by Eq. (62). 

Reaction energy diagrams for two hypothetical reactions. The rate-limiting step in each is determined by the difference in height between a low point and a subsequent high point. In (a), the first step is rate-limiting in (b), the second step is rate-limiting. 

At high pressnres or concentrations eqnilibrium is established in the first step and the second step is rate limiting. First order kinetics are observed. Chain reactions proceed throngh a series of elementary reactions, one or more of which is repeated many times. 

It is commonly assumed that the second step is rate limiting. Land-auer and Rydon (206,284) cited the fact that action of methyl iodide on triethyl phosphite produces almost exclusively diethyl methyl phos-phonate as evidence for virtual completion of the first step before any appreciable amount of ethyl iodide has been liberated in the valency expansion step. However, the methyl halides are exceptionally reactive members of their homologous series for substitution reactions in general and for the Michaelis-Arbuzov reaction in particular (26) also, when other alkyl halides are employed, back reaction of the halide formed frequently does occur (177). 

For a reaction with time-independent stoichiometry and a proposed two-step reaction mechanism in which the second step is rate-limiting then the overall rate of reaction is determined by the second step and the first step can be treated as a rapidly established pre-equilibrium. 

In this mechanism, the second step is rate limiting, and the adsorption of NiOHads follows the Langmuir isotherm. Find the values for the following quantities expressed in base-10 logarithms ... 

The second condition is that the rate law predicted by the mechanism must be consistent with the experimentally observed rate law. Since the second step is rate limiting, we write the following expression for the rate law ... 

If the second step is rate-limiting, the first step can be assumed to be at equilibrium. We now present a simple equilibrium theory of adsorption in order to discuss the equilibrium of the first step of this mechanism. 

We assume that the second step is rate-limiting. Using Eq. (13.1-8) for the assumed equilibrium of the first step, the rate is given by... 

Assume that the second step is rate-limiting. 

Since molecules must collide to react, this mechanism means that the B molecules from the fluid phase must collide with the adsorbed A molecules without first being adsorbed. If the second step is rate-limiting, the rate law is... 

In either of these mechanisms, it is possible for different metals that either the first step or the second step is rate-limiting. If the first step of the mechanism of Eq. (13.5-27) is rate-limiting in both directions,... 

Do we have any information about the slow step of the process Well, since we know that the reaction of iodonium salts 1 with /jora-substituted A-(arenesul-fonyl)benzaldimines is sensitive to the nature of the substituents present on the sulfonyl aromatic ring, the imines must be necessarily involved in the rate-determining step of the reaction. In consequence, if the reaction between the ylides and the imines (second step) is rate-limiting, the formation of the ylides (first step) must be a fast pre-equilibrium. 

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