Reaction constant physical significance

Sterigmatocystin, 48 Stevens rearrangements, 293 Stobbe reaction, 228 Substituent constant, a, 362 constancy of, 368, 372 determination of, 363 physical significance of, 364 and, 362... 

Km is the Michaelis constant representing the equilibrium enzyme-substrate intermediate, fcr the rate-determining constant, cE0 the initial enzyme concentration, and S the concentration of substrate. The physical significance is that the reaction rate is proportional to the substrate concentration at low values, but tends to maximum at higher values. If initial rate experiments are conducted then the limit of the reaction rate will correspond to a maximum initial rate Vmr, = krcE0. By replacing it into Eq. (15.1) the following kinetic expression is obtained ... 

A review of the physical significance of the dimensionless parameters is appropriate at this point. S is the maximum possible adiabatic temperature rise, scaled by the temperature coefficient of reaction rate. It is a measure of the sensitivity of the reaction to changes in operating conditions, and is sometimes designated by "B" in the literature. "D" is the residence time multiplied by the specific rate constant at the inlet, often called the "number of reaction units", x is the temperature rise, scaled by the temperature coefficient of reaction rate. The maximum possible value of x is S. 

Thus, Kn, the Michaelis constant, is a dynamic or pseudo-equilibrium constant expressing the relationship between the actual steady-state concentrations, rather than the equilibrium.concentrations. If Aj, is very small compared to A-i, reduces to K. A steady-state treatment of the more realistic reaction sequence E+ S ES EP E + P yields the same final velocity equation although now Km is a more complex function, composed of the rate constants of all the steps. Thus, the physical significance of K cannot be stated with any certainty in the absence of other data concerning the relative magnitudes of the various rate constants. Nevertheless, represents a valuable constant that relates the velocity of an enzyme-catalyzed reaction to the substrate concentration. Inspection of the Henri-Michaelis-Menten equation shows that Km is equivalent to the substrate concentration that yields half-maximal velocity ... 

The Arrhenius equation can be developed based on the Boltzmann s law. The physical significance can be better explained based on a comparison of equation (6.17) and (6.18). For example, the frequency factor can be compared with the number of particles which are available in the reaction zone and can potentially react to form the product. Reaction velocity constant can be compared with the number of molecules that has energy higher than the activation energy. 

It was possible to estimate parameters for OH complexes of K" ", Li" ", and Na in the fitting process. Of these complexes, the WATEQ and amended WATEQ models included a OH complex for Ba, and the value for the stability constant was similar to that calculated by the fitting process. In the fit model, the hi (Equation 6) parameters for the OH complexes of K, Li", and Na were 0.56, 0.4, and 0.42 respectively. The physical significance of these large h values is not clear. When the association reactions were written in terms of OH , the stability constants were -0.09,0.44, and 0.06, respectively. Calculations indicate that, in a 1.0 molal KOH solution, the concentration of the KOH complex is 0.14 molal. Additional experimental evidence from titrations or spectroscopy is needed to determine whether this ion pair actually exists and whether this concentration is reasonable. If there is no evidence that the OH salts are partially associated in solution, the large stability constants may indicate that specific-ion interactions are involved that can not be accounted for by the ion-association approach. 

The proton involved stoichiometrically in the reaction has been neglected in these formulations, and Keq/H+ is the true, pH-independent equilibrium constant. Consideration of the physical significance of < b and q (Table I) shows that the equilibrium constant for the reaction of enzyme-bound coenzymes and the substrates, EA - - B EP -p Q, is... 

We will now focus on the time-dependence of the slow component and its physical significance. Analysis of this part of the signal in all the alcohols reveals an exponential growth whose reciprocal rate constant we have called and plotted in Table I, in conjunction with other properties of the liquids. The data are quoted to 10%. In alcohols where C , the number of carbon atoms, is greater than 6, the first-order signal Uiils off into an even slower component but this may in part be because e formed at early times are now undergoing chemical reaction at times > 10 s. 

Here feo would presumably be the value of the rate constant as P —> 0, however, the precise physical significance of this may be a httle hard to grasp (i.e., is there a reaction at P = 0 ). It is probably just as well to view In A o as a constant that follows from the linear relationship. 

Kozlov, G. V Zaikov, G. E. The physical significance of reaction rate constant in Euclidean and fractal spaces at polymers thermooxidative degradation consideration. Theoretical Principles of Chemical Technology, 2003, 37(5), 555-557. 

It follows from (3.19) that equation (3.6) and (3.7) are accurate within a constant magnitude for definition of the relative contribution of an individual step and a chemical species in the chosen output parameter F of the reaction system. They also enable to predict accurately the behavior of the parameter F when the step rates and concentrations of species are varied. In fact, equation (3.19) enables to see clearly their physical significance. 

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