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Lindemann-Christiansen Mechanism

In principle, unimolecular reactions should be one of the most conceptually simple reactions in chemistry. However, the history of the understanding of simple decomposition processes, such as [Pg.209]

The energised molecule may undergo de-energisation by collisions with a normal molecule, or it may undergo a reaction of molecularity equal to one to form products. There are, therefore, three distinct processes in this mechanism with their own rates (i) the rate of energisation is (ii) A can be de-energised at a rate i[A ][A] and (iii) A can be converted into products at a rate 2 [A ]. [Pg.210]

The rate of product formation depends on the [A ], which can be found from a steady [Pg.210]

In the vapour phase, at high pressures, one has A j [A ] and the rate of reaction [Pg.210]

At high pressures the reaction is a first-order process. Under those conditions, the rate of energisation and de-energisation are relatively fast steps, which can be treated as a fast preequilibrium. Thus, the rate determining step is the transformation of A into products. [Pg.210]


Note The Lindemann mechanism was also suggested independently by Christiansen. Hence, it is also sometimes referred to as the Lindemann-Christiansen mechanism. The theory of unimolecular reactions was further developed by Hinshelwood and refined by Rice, Rampsberger, Kassel and Marcus. [Pg.74]

Although the theory does need to be improved in a number of details before it can provide a quantitative description of experiment, the observation of fall-off from first order at high pressures to second order at low pressures is correctly explained by the Lindemann-Christiansen mechanism, and modem theories of unimolecular reactions are based on this mechanism. [Pg.6]

The second difficulty with the Lindemann-Christiansen mechanism becomes apparent when experimental data are plotted in another way... [Pg.212]

The first difficnlty of the Lindemann-Christiansen mechanism is associated with the fact that first-order rates are maintained down to lower concentrations than appear to be... [Pg.212]

According to the Lindemann-Christiansen hypothesis, formulated independently by both scientists in 1921, all molecules acquire and lose energy by collisions with surrounding molecules. This is expressed in the simplified form of the Lindemann mechanism, in which we use an asterisk to indicate a highly energetic or activated molecule, which has sufficient energy to cross the barrier towards the product side, and M is a molecule from the surroundings M may be from the same type as A ... [Pg.107]

After Lindemann and Christiansen put forward their mechanism, experimental work was carried out to verify if the unimolecular reactions did become second order at sufficiently low pressures. Figure 8.1 illustrates the order of dimethyl ether decomposition in the vapour phase as a function of the addition of a foreign gas. In qualitative terms, the mechanism of Lindemann-Christiansen gives a good account of the experimental observations,... [Pg.210]

When 8 is sufficiently high, every energised molecule A is essentially an activated species A, but this conditions depends on the value of s as shown in Figure 8.4. Figure 8.5 illustrates the apphcation of Lindemann-Christiansen-Hinshelwood, RRK mechanisms to the isomerisation of cyclopropane as a function of pressure [4]. [Pg.216]

In this complex state of affairs it seemed of interest to examine some reactions at pressures so low that some differentiation between the proposed mechanisms would be possible, or at least some experimental data in a simplified form would be available. It is evident that, at sufficiently low pressures, a profound modification of the velocity constant should take place whether the mechanism be that of Christiansen and Kramers, Lindemann, Perrin or Rodebush. The relation between collision frequency and observed reaction rate at this point would also be of considerable significance.11... [Pg.3]

Lindemann proposed the following mechanism, which was also advanced by Christiansen ... [Pg.545]


See other pages where Lindemann-Christiansen Mechanism is mentioned: [Pg.209]    [Pg.211]    [Pg.209]    [Pg.211]    [Pg.209]    [Pg.428]   


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