Chemical reactions duration

Hence, the results considered above have shown the possibility of product of transesterification reaction (heptylbenzoate molecule) stmcture regulation by filler-catalyst change which are used as metal oxides nanoparticles. The indicated stmcture change results to active time essential variation, i.e., real chemical reaction duration, namely, for the considered conditions of reaction approximately in 20 times. In its turn, this tells on transesterification reaction main characteristics variation. The dependence of conversion degree on active time for all the used metal oxides is described by general linear correlation [63],... 

Calculation of the characteristic mixing time and chemical reaction duration, in relation to the mixing and reaction zones lengths, in turbulent reactors reveals the feasibility criterion for fast chemical processes using tubular turbulent devices [29] for polymer synthesis (polymerisation) ... 

The effective heat conduction coefficient Chemical reaction duration... 

The assumption that k values are constant over the entire duration of the reaction breaks down for termination reactions in bulk polymerizations. Here, as in Sec. 5.2, we can consider the termination process—whether by combination or disproportionation to depend on the rates at which polymer molecules can diffuse into (characterized by kj) or out of (characterized by k ) the same solvent cage and the rate at which chemical reaction between them (characterized by kj.) occurs in that cage. In Chap. 5 we saw that two limiting cases of Eq. (5.8) could be readily identified ... 

Another variation is the mode-locked dye laser, often referred to as an ultrafast laser. Such lasers offer pulses having durations as short as a few hundred femtoseconds (10 s). These have been used to study the dynamics of chemical reactions with very high temporal resolution (see Kinetic LffiASURELffiNTS). 

The availability of lasers having pulse durations in the picosecond or femtosecond range offers many possibiUties for investigation of chemical kinetics. Spectroscopy can be performed on an extremely short time scale, and transient events can be monitored. For example, the growth and decay of intermediate products in a fast chemical reaction can be followed (see Kinetic measurements). 

Anions of another group were derivatized with formation of gaseous chemiluminescing species. Chemical reaction - gas extraction has been used with chemiluminescence detection in the stream of canier gas in on-line mode. Rate of a number of reactions has been studied as well as kinetic curves of extraction of gaseous products. Highly sensitive and rapid hybrid procedures have been developed for the determination of lO, BrO, CIO, CIO, NO,, N03, CrO, CIO, Br, T, S, 803 with detection limits at the level of pg/L, duration of analysis 3 min. 

As the blast wave expands, it decays in strength, lengthens in duration, and slows down, both because of spherical divergence and because the chemical reaction is over, except for afterburning as the hot explosion products mix with the surrounding air. 

In many reacting flows, the reactants are introduced into the reactor with an integral scale L that is significantly different from the turbulence integral scale Lu. For example, in a CSTR, Lu is determined primarily by the actions of the impeller. However, is fixed by the feed tube diameter and feed flow rate. Thus, near the feed point the scalar energy spectrum will not be in equilibrium with the velocity spectrum. A relaxation period of duration on the order of xu is required before equilibrium is attained. In a reacting flow, because the relaxation period is relatively long, most of the fast chemical reactions can occur before the equilibrium model, (4.93), is applicable. 

Chapter 16 - It is shown, that there is principal difference between the description of generally reagents diffusion and the diffusion defining chemical reaction course. The last process is described within the framework of strange (anomalous) diffusion concept and is controled by active (fractal) reaction duration. The exponent a, defining the value of active duration in comparison with real time, is dependent on reagents structure. 

The overall effect of the preceding chemical reaction on the voltammetric response of a reversible electrode reaction is determined by the thermodynamic parameter K and the dimensionless kinetic parameter . The equilibrium constant K controls mainly the amonnt of the electroactive reactant R produced prior to the voltammetric experiment. K also controls the prodnction of R during the experiment when the preceding chemical reaction is sufficiently fast to permit the chemical equilibrium to be achieved on a time scale of the potential pulses. The dimensionless kinetic parameter is a measure for the production of R in the course of the voltammetric experiment. The dimensionless chemical kinetic parameter can be also understood as a quantitative measure for the rate of reestablishing the chemical equilibrium (2.29) that is misbalanced by proceeding of the electrode reaction. From the definition of follows that the kinetic affect of the preceding chemical reaction depends on the rate of the chemical reaction and duration of the potential pulses. 

The effect of the volume and the surface catalytic reaction is sketched in Figs. 2.80 and 2.81, respectively. Obviously, the voltammetric behavior of the mechanism (2.188) is substantially different compared to the simple catalytic reaction described in Sect. 2.4.4. In the current mechanism, the effect of the volume catalytic reaction is remarkably different to the surface catalytic reaction, revealing that SWV can discriminate between the volume and the surface follow-up chemical reactions. The extremely high maxima shown in Fig. 2.81 correspond to the exhaustive reuse of the electroactive material adsorbed on the electrode surface, as a consequence of the synchronization of the surface catalytic reaction rate, adsorption equilibria, mass transfer rate of the electroactive species, and duration of the SW potential pulses. These results clearly reveal how powerful square-wave voltammetry is for analytical purposes when a moderate adsorption is combined with a catalytic regeneration of the electroactive material. This is also illustrated by a comparative analysis of the mechanism (2.188) with the simple surface catalytic reaction (Sect. 2.5.3) and the simple catalytic reaction of a dissolved redox couple (Sect. 2.4.4), given in Fig. 2.82. 

The primary objective of the shock tube tests is to enable only reactions that occur at the catalyst surface, which is done by removing all aspects of mass transport and to quickly stop all reactions in precisely defined time duration. The right choice of a test mixture composition can help to isolate the chemical reaction under investigation, while varying initial conditions allows for a wide range of concentration, pressures and temperatures. 

It is suggested that the objection can be overcome if initiation temperature is inde-. pendent of the size and duration of the hot spot and if these latter quantities are important only as they influence the hot spot temperature. In these spots, at least, the temperature in the shock front may be high enough to initiate chemical reaction in the ordinary sense. This brings both initiation and the subsequent chemical reaction into the domain of ordinary chemical kinetics (Ref 5,p 216)... 

Detonation, Reaction Zone in. When a stick of explosive is detonated from one end,the chemical reaction which completely transforms the stick to burnt gases is of extremely short duration and for this reason the layer where the reaction takes place is very narrow. This layer is known as reaction zone. It is that part of the detonation zone which is behind the very thin shock zone. 

The above models describe a simplified situation of stationary fixed chain ends. On the other hand, the characteristic rearrangement times of the chain carrying functional groups are smaller than the duration of the chemical reaction. Actually, in the rubbery state the network sites are characterized by a low but finite molecular mobility, i.e. R in Eq. (20) and, hence, the effective bimolecular rate constant is a function of the relaxation time of the network sites. On the other hand, the movement of the free chain end is limited and depends on the crosslinking density 82 84). An approach to the solution of this problem has been outlined elsewhere by use of computer-assisted modelling 851 Analytical estimation of the diffusion factor contribution to the reaction rate constant of the functional groups indicates that K 1/x, where t is the characteristic diffusion time of the terminal functional groups 86. ... 

A period of induction is characteristic of chemical reactions which take place in a series of intermediate stages. This is a necessary consequence of the law of mass action. The duration of the period depends on the relative magnitude of the velocity constants of the intermediate reactions. For example, with the reaction A=M=B, the rate of formation of the intermediate compound, M in the A=M reaction, will be quickest at the start, and the rate of formation of B by the destruction of M in the M=B reaction will be slowest at first, and increase with time as the amount of M accumulates in the system. At first, during the period of acceleration, the speed of the A=M reaction exerts a preponderating influence and M accumulates in the system but the increasing speed of the M=B reaction gradually neutralizes the effect of the first reaction, until the rate of formation of M by the A=M reaction is equal to the rate of its destruction by the M=B reaction, and finally, the M is consumed faster than it is formed. The amount of M in the system at any moment thus determines the rate of formation of B, so that the curves showing (i) the rate of formation of B, and (ii) the amount of M in the system at different moments, are similar in shape. This is illustrated by the dotted line in Fig. 6. The duration of the period of induction naturally depends upon the relative speeds of the two reactions. If the rate of formation of the intermediate compound is immeasurably fast, there will be no appreciable period of induction. 

Fig 13 Critical acceleration and energy release rate curves determined from long-duration pulse experiments, as functions of shock amplitude v in PBX 9404. Energy rate shown is the net result of mechanical dissipation and exothermic chemical reaction. Following thermochemical convention, energy release rate due to exothermic reaction is denoted as a negative value of H ... 

The possibility of reflection of electrons by an evanescent wave formed upon the total internal reflection of femtosecond light pulses from a dielectric-vacuum interface is quite realistic. The duration of the reflected electron pulses may be as long as 100 fs. In the case of electrons reflecting from a curved evanescent wave, one can simultaneously control the duration of the reflected electron pulse and affect its focusing (Fig. lc). Of course, one can imagine many other schemes for controlling the motion of electrons, as is now the case with resonant laser radiation of moderate intensity [9, 10]. In other words, one can think of the possibility of developing femtosecond laser-induced electron optics. Such ultrashort electron pulses may possibly find application in studies into the molecular dynamics of chemical reactions [1,2]. 

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