Rate-limiting steps, in reactions

The rate-limiting step in Reaction Scheme 10 was determined to be conversion of trans- Ir(N02)4Cl2]3 to [Ir(N02)6]3. The kinetics were studied gravimetrically between 80 °C and... 

It is assumed that the reaction catalyzed by RubisCO is a rate-limiting step in reactions of photosynthetic carbon fixation expressed as follows in the lump ... 

As with the other surface reactions discussed above, the steps m a catalytic reaction (neglecting diffiision) are as follows the adsorption of reactant molecules or atoms to fomi bound surface species, the reaction of these surface species with gas phase species or other surface species and subsequent product desorption. The global reaction rate is governed by the slowest of these elementary steps, called the rate-detemiming or rate-limiting step. In many cases, it has been found that either the adsorption or desorption steps are rate detemiining. It is not surprising, then, that the surface stmcture of the catalyst, which is a variable that can influence adsorption and desorption rates, can sometimes affect the overall conversion and selectivity. 

Tubular reactors often offer the greatest potential for inventory reduction. They are usually simple, have no moving parts, and a minimum number of joints and connections that can leak. Mass transfer is often the rate-limiting step in gas-liquid reactions. Novel reactor designs that increase mass transfer can reduce reactor size and may also improve process yields. 

According to the Hammond postulate (Section 6.10), any factor that stabilizes a high-energy intermediate also stabilizes the transition state leading to that inlermediate. Since the rate-limiting step in an S l reaction is the spontaneous, unimolecLilar dissociation of the substrate to yield a carbocation, the reaction is favored whenever a stabilized carbocation intermediate is formed. The more stable the carbocation intermediate, the faster the S l reaction. 

The rate-limiting step in the reaction 2 NaH2P04 = Na2H2P207 + H20... 

Figure 2.8. Rate-limiting steps in a CVD reaction (a) surface reaction kinetics control, (b) diffusion control.

In the A sector (lower right), the deposition is controlled by surface-reaction kinetics as the rate-limiting step. In the B sector (upper left), the deposition is controlled by the mass-transport process and the growth rate is related linearly to the partial pressure of the silicon reactant in the carrier gas. Transition from one rate-control regime to the other is not sharp, but involves a transition zone where both are significant. The presence of a maximum in the curves in Area B would indicate the onset of gas-phase precipitation, where the substrate has become starved and the deposition rate decreased. 

Consider the NO/N02-catalyzed ozone destruction cycle, reactions 5 and 6 in Section 5.4.3. One could perform a calculation to determine which reaction is the rate-limiting step (i.e., the slowest step that determines the rate of the overall reaction) in this cycle. In this case, a theoretical doubling of ks reduces the ozone concentration by about 2%. On the other hand, doubling kf, reduces the ozone concentration by nearly 50%. (a) Which reaction is the rate-limiting step in N0/N02-catalyzed ozone destruction (b) The concentrations of NO and NO2 are [NO] = 2.9 X 10 /cm and [NO2] = 6.1 x 10 /cm. How do these data support or refute your answer to (a) ... 

Hence, l/K only approximates l/K under conditions where the association and dissociation of the ES complex is rapid relative to the rate-limiting step in catalysis. For the many enzyme-catalyzed reactions for which + kj is not approximately equal to k j, IIK will underestimate IIK,. 

As with chlorine-containing oxidants, JV-bromo species have been used to oxidize sulphoxides to sulphones (with no bromine incorporation) through the initial formation of a bromosulphonium ion, by nucleophilic attack of the sulphoxide sulphur atom on the electrophilic halogen atom. Such reactions involve JV-bromosuccinimide ° bromamine-T, iV-bromoacetamide ° and iV-bromobenzenesulphonamide. All reported studies were of a kinetic nature and yields were not quoted. In acid solution all oxidations occurred at or around room temperature with the nucleophilic attack on the electrophilic bromine atom being the rate-limiting step. In alkaline solution a catalyst such as osmium tetroxide is required for the reaction to proceed . ... 

HPLC is a very powerful technique for qualitative and quantitative analysis. In the support of process development, HPLC plays an important role in monitoring a reaction, since each reaction component can be quantitated. In this role, the HPLC method must be fast, rugged, and specific, capable of separating all reactants, products, and byproducts. Development of appropriate analytical methods is often a rate-limiting step in process development. 

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