Reactions Bodenstein

Accordingly, for a bimolecular reaction, Bodenstein and Wohlgast find... 

The scheme proposed in (18) and (19) resembles one frequently applied to multi-step reactions (Bodenstein, 1913). If a steady-state concentration is assumed for the complex (and for the chain carrier RO2 radicals) the overall rate of the process consisting of steps (18) and (19) is... 

Why did adding CO slow up the reaction Bodenstein and Fink drew on earlier work by Walther Nernst to suggest an answer. They assumed that CO and O2 would only react rapidly at the platinum surface. The CO, they suggested, formed a film several molecules thick on that surface - the more CO, the thicker the film. And the thicker the film, the longer it took the O2 to diffuse through and get to the platinum, so the slower the reaction. ... 

Definitions of a Catalyst.—(1) A catalyst is a substance that accelerates a reaction but cannot induce a reaction (Bodenstein, 1902). 

This equilibrium has been extensively studied by Bodenstein. Unlike the other halogen-hydrogen reactions, it is not a chain reaction but a second order, bimolecular, combination. 

Hydrogen Bromide H2 -i- Bi"2 2HBr (Bodenstein, 1906). The chain of reactions is ... 

Mixing of product and feed (backmixing) in laboratory continuous flow reactors can only be avoided at very high length-to-diameter (aspect) ratios. This was observed by Bodenstein and Wohlgast (1908). Besides noticing this, the authors also derived the mathematical expression for reaction rate for the case of complete mixing. 

Humans can not know the ultimate and detailed true reaction mechanism of any reaaJon, or the kinetics that can be derived from it.. Bodenstein (1906) studied the mechanism of the H2 + Br2 = 2 HBr reaction and after several decades of work and dozens of publications wrote the final paper on the subject. Within a few years one of his students published a correction to Bodenstein s explanations. 

Bodenstein and Lind [3] first studied the thermal reaction over the temperature range of 500-600 K. The relative reaction rates of hydrogen and bromine and the formation of hydrogen bromide are ... 

Chain reactions ivere discovered around 1913, ivhen Bodenstein and Dux found that the reaction betv een H2 and CI2 could be initiated by irradiating the reaction mixture ivith photons. They ivere surprised to find that the number of HCl molecules per absorbed photon, called the quantum yield, is around 10 Nernst explained this phenomenon in 1918 the photon facilitated the dissociation of CI2 into Cl radicals (the initiation step), which then started the following chain process ... 

The theoretical approach involved the derivation of a kinetic model based upon the chiral reaction mechanism proposed by Halpem (3), Brown (4) and Landis (3, 5). Major and minor manifolds were included in this reaction model. The minor manifold produces the desired enantiomer while the major manifold produces the undesired enantiomer. Since the EP in our synthesis was over 99%, the major manifold was neglected to reduce the complexity of the kinetic model. In addition, we made three modifications to the original Halpem-Brown-Landis mechanism. First, precatalyst is used instead of active catalyst in om synthesis. The conversion of precatalyst to the active catalyst is assumed to be irreversible, and a complete conversion of precatalyst to active catalyst is assumed in the kinetic model. Second, the coordination step is considered to be irreversible because the ratio of the forward to the reverse reaction rate constant is high (3). Third, the product release step is assumed to be significantly faster than the solvent insertion step hence, the product release step is not considered in our model. With these modifications the product formation rate was predicted by using the Bodenstein approximation. Three possible cases for reaction rate control were derived and experimental data were used for verification of the model. 

Bellman et al. (1967) have considered the estimation of the two rate constants k and k2 in the Bodenstein-Linder model for the homogeneous gas phase reaction of NO with 02 ... 

In 1906 Bodenstein and Lind (24) investigated the gas phase homogeneous reaction between molecular bromine and molecular hydrogen at pressures in the neighborhood of 1 atm. They fitted their experimental data with a rate expression of the form... 

ILLUSTRATION 4.3 USE OF THE BODENSTEIN STEADY-STATE APPROXIMATION TO DERIVE A RATE EXPRESSION FROM A CHAIN REACTION MECHANISM... 

The rate law obtained from a chain-reaction mechanism is not necessarily of the power-law form obtained in Example 7-2. The following example for the reaction of H2 and Br2 illustrates how a more complex form (with respect to concentrations of reactants and products) can result. This reaction is of historical importance because it helped to establish the reality of the free-radical chain mechanism. Following the experimental determination of the rate law by Bodenstein and Lind (1907), the task was to construct a mechanism consistent with their results. This was solved independently by Christiansen, Herzfeld, and Polanyi in 1919-1920, as indicated in the example. 

The reaction between hydrogen and bromine was studied by Bodenstein Lind (2 physik Chem 57 168, 1907). Data were obtained at 277.5 C of time,... 

This reaction and the synthesis of HBr have also received much less attention than the corresponding reactions of the HI system. The problem of the mechanism of the H2+Br2 reaction which Bodenstein and Lind33 found to be complex was later solved independently by Christiansen34, Herzfeld35 and Polanyi36. The well-known mechanism and the kinetic equation resulting from the stationary-state solution are given below... 

The kinetics of neither the photochemical nor the thermal decomposition of this compound have received much attention. Bodenstein et al.53 in 1937 showed that the hydrogen and fluorine reaction could not be photosensitised by chlorine at room temperature. 

The thermal and photochemical syntheses of phosgene have been very thoroughly investigated. Apart from the initiation process the mechanisms of the two reactions are essentially the same. A long controvervy between Bodenstein et al.125 and Rollefson and Lenher126 was finally settled in the favour of the former and their mechanism is shown below. 

Henri and Michaelis-Menten kinetics assumed that the rate of formation of products was much less than that for the back reaction from ES to yield E + S. Van Slyke assumed the reverse. A more rigorous formulation was offered by Briggs and Haldane (1925) using steady-state assumptions previously applied to chemical kinetics by Bodenstein (1913). 

There are many ways to measure the concentrations of reacting species or species formed during the reaction, such as there are gc, UV-visible spectroscopy, IR spectroscopy, refiactometry, polarometry, etc. Conversion can be monitored by pressure measurements, gas-flow measurements, calorimetry, etc. Data are collected on a computer and many programmes are available for data analysis [3,4], The two-reaction system described above can be treated graphically, if it fulfils either the Bodenstein or Michaelis-Menten criteria. 

In most instances, two reacting molecules do not react directly as H2 and I2 do rather one molecule dissociates first to form radicals. These radicals then initiate a chain of steps. Interestingly, this procedure occurs in the reaction of H2 with another halogen, Br2. Experimentally, Bodenstein [12] found that the rate of formation of HBr obeys the expression... 

Bodenstein explained this result by suggesting that the H2-Br2 reaction was chain in character and initiated by a radical (Ih ) formed by the thermal dissociation of Br2. He proposed the following steps ... 

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