Bodenstein and Lind

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 ... 

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... 

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. 

This has the same form as that obtained experimentally by Bodenstein and Lind earlier. 

The study of the reactions of the simple free radicals begun by Bodenstein and Lind in 1906 on the kinetics of gas phase reactions showed that the reactions of H2 with CI2 and Bt2 were complex processes/ and a radical chain mechanism for these reactions (equations 14-18) was proposed in 1919 by Christiansen, Herzfeld, and Polanyi/ The theoretical basis for understanding these reactions in terms of free radicals was presented by G.N. Lewis in 1916, with the theory of the electron pair bond, and free radicals, or odd molecules / Further studies on chain reactions including the extension to explosions in gaseous systems were made by Hinshelwood and by Semenovwho shared the Nobel Prize in 1956. 

Although all reactions showing a closed sequence could be considered to be catalytic, there is a difference between those in which the entity of the active site is preserved by a catalyst and those in which it survives for only a limited number of cycles. In the first category are the truly catalytic reactions, whereas the second comprises the chain reactions. Both types can be considered by means of the steady-state approximation, as in Christiansen s treatment. This important development dates to 1919 (reaction between hydrogen and bromine reported earlier by Bodenstein and Lind. 

The formation of hydrogen bromide from its elements takes place in an unexpectedly complicated manner. Bodenstein and Lind measured the velocity at 200° to 300° C. and found that it could be expressed by the equation... 

At a temperature of 250°C in experiments by Bodenstein and Lind as well only a very slow chemical reaction occurred, requiring long hours to complete. 

In a not too complicated case, e.g., in the case of the hydrogen-bromine reaction investigated so thoroughly by the Bodenstein school, it can be shown with certainty that its well known mechanism is really the only one which conforms with the (very accurate) experiments by Bodenstein and Lind and later experimenters. In this and often in more complicated cases, too, the calculations permit expressing the time from the beginning of the experiment by means of the sum of a number of known functions of the degree of advancement x, each multiplied by a constant. 

The first paper by Christiansen treating the disentanglement of the mechanism of a chemical reaction was the one from 1919 (9). In this the mechanism of the hydrogen bromide formation was elucidated on the basis of the experiments of 1907 by Bodenstein and Lind (16a). It was independent of but simultaneous with the papers by Herzfeld (8) and Polanyi (10). 

In 1906, Bodenstein and Lind showed that the kinetics of the reaction of H2 and Br2 (which proceeds at a conveniently measurable rate between 230 and 300 C) could be presented empirically by the equation... 

Bodenstein and Lind have studied the thermal reaction between H2 and Br2 to form HBr. Their careful study showed this reaction to be of apparently much greater complexity than the H2-I2 reaction. As was pointed out later in the interpretations of this data by Christiansen, Herzfeld, and Polanyi the reaction proceeds by a free radical chain mechanism involving bromine and hydrogen atoms. Assuming the bromine atom concentration to be governed by the Br2 = 2Br thermal equilibrium, the mechanism of HBr formation is... 

The most self-consistent value of k /k found by Bodenstein and Lind was 10, independent of temperature. This result together with K and k furnishes ki, the rate coefficient for reaction (2), as given in Table 6. It should be noted that /c2 is not sensitive to k jk if [HBr] is small. 

KINETIC DATA FOR THE OVERALL REACTION OF HYDROGEN AND BROMINE AND FOR THE REACTION Bt2-1-H2 FROM THE RESULTS OF BODENSTEIN AND LIND ... 

This equation has the same form as Eq. (32.64), the empirical equation of Bodenstein and Lind. (The integrated form of this equation has no particular utility.)... 

The classical gas phase between H2 and Br2 to form HBr between 200 and 300°C is not limited by equilibrium. Yet Bodenstein and Lind found that its rate is inhibited by its product." Although the authors obtained the correct rate expression, they were unable to explain their kinetic observations. The explanation came 13 years later, independently and almost simultaneously. Without... 

This reaction was studied by Bodenstein and Lind nearly 90 years ago, and the rate law found was written as... 

The homogeneous reaction between H2 and Br2 to form HBr was investigated in 1906 by Bodenstein and Lind [8], who studied it in the range 230-300°C. Their empirical representation of the rate was given by... 

So far here and in Chapter 7, we have considered straightforward analysis of reaction rates measured by the extent of the reaction based on mole mmover rate, but there are many reactions which follow more complicated rate equations. The classic problem of this more complicated type was first treated by Bodenstein and Lind [6] and later by Christiansen [7], Herzfeld [8], and Polanyi [9]. The first experimental data for the reaction of hydrogen and bromine were fitted accurately to an expression, which is far from what might be expected ... 

The concept of a reaction mechanism was undoubtedly a product of nineteenth chemistry, but it was not until the turn of the century, when the idea was inseparably joined with chemical kinetics, that the possibility of meaningful conclusions was established by the experiments of Lapworth At about the same time, Bodenstein and Lind were studying the gas-phase reaction of hydrogen and bromine, obtaining a rate law which was mechanistically interpreted thirteen years later by Christiansen He rzfeld and Polanyi These triumphs, together with the subsequent successes of Rice and Herzfeld mechanisms for the decomposition of organic molecules, provided considerable impetus to the idea that it was only necessary to discover the correct mechanisms in order to account for most chemical reactions. 

In 1907, Bodenstein and Lind studied the kinetics of the gas reaction H2 + Br2 — 2HBr in the temperature interval from 200 to 300 °C. They experimentally established the kinetic law and formulated it as follows ... 

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