Reaction rate zero-order

In the calculation results, shown in Figure 28.4, phenol concentration decreases with time at a constant rate for about the first 30 days of reaction. Over this interval, the concentration is greater than the value of K, the half-saturation constant, so the ratio m/(m + K ) in Equation 28.9 remains approximately constant, giving a zero-order reaction rate. Past this point, however, concentration falls below K and the reaction rate becomes first order. Now, phenol concentration does not decrease linearly, but asymptotically approaches zero. 

Zero-order reactions Rates for these reactions don t depend on the concentration of any species but simply proceed at a characteristic and constant rate. 

A comparison of this analysis with the results shown in Figures 2 and 3 points to the fact that for our present kinetics, the behavior is dominated by zero order reaction rate. This is understandable too, considering the very low values of 1 (=1.28... 

In this respect, the overall mineralization rate of phenol has often been approximated with a zero-order reaction rate (Salaices et al., 2004) as it follows a fairly straight line. For the Fe-assisted PC reaction, however, this approximation cannot be applied given the sharp change of slope in the last part of the photoconversion reaction. Thus, a more complex kinetic rate equation needs to be developed to account for this behavior. 

Reproducible zero-order reaction rates for the [W(CN)g] /S203 " reaction could be obtained only upon addition of Na2EDTA, which is similar to that of the [Fe(CN)g] tional term in the rate law,... 

When an explosive slowly decomposes, the products may not follow the previously described hierarchy or be at the maximum oxidation states. The nitro, nitrate, nitramines, acids, etc., in an explosive molecule can break down slowly. This is due to low-temperature kinetics as well as the influence of light, infrared, and ultraviolet radiation, and any other mechanism that feeds energy into the molecule. Upon decomposition, products such as NO, NO2, H2O, N2, acids, aldehydes, ketones, etc., are formed. Large radicals of the parent explosive molecule are left, and these react with their neighbors. As long as the explosive is at a temperature above absolute zero, decomposition occurs. At lower temperatures the rate of decomposition is infinitesimally small. As the temperature increases, the decomposition rate increases. Although we do not always, and in fact seldom do, know the exact chemical mechanism, we do know that most explosives, in the use range of temperatures, decompose with a zero-order reaction rate. This means that the rate of decomposition is usually independent of... 

Equation (6) will give a zero order reaction rate in total concentration (pressure) when G is small compared to P However, it leads to a mole fraction dependence on dilution with competing molecules as demanded by the dilution experiments at 360°C. In only two cases is a... 

If the destruction of a component is presumed to be zero-order, a plot of C vs. t should give a straight line. Certain losses of vitamin C, particularly in frozen foods, are presumed to follow first-order kinetics (89). Labuza (76) observed that zero-order reaction rates for quahty losses may be assumed in some fluctuating temperature studies, but this may lead to a miscalculation of predicted changes. Therefore, from a theoretical standpoint, it is important that the proper order be used for predictions. In general, ascorbic acid destruction is assumed to be first-order, or pseudo first-order (17,27) except under specific conditions of heat and moisture (79). 

All the time-dependent terms in Equation 50 assembled between the braces are independent of the oxygen consumption rate, v. This means that the rate at which the concentration C at any depth approaches a steady-state value (dC/dt) is independent of the zero order reaction rate constant. The time-dependent terms contain, however, the eddy diffusion coefficient and advection velocity, and the rate of approach to steady-state is therefore dependent on these two physical characteristics of the environment. 

In pure systems under carefully controlled conditions, the reaction order is often 0,1, or 2. These reaction rates can be plotted linearly with respect to time by choosing the appropriate concentration axis (Fig. 3.8). The reaction order can be obtained by fitting data to such plots. Zero-order reaction rates are independent of the amount or concentration of the reactant studied ... 

Calculating the time to reach a given [A] in a zero-order reaction (rate = A ) (511) ... 

It shall be assumed that a simple conversion of A to B shall be performed in a batch reactor. It is further assumed that A is available in a close to infinitive amount, this way allowing the neglection of any consumption of A with progressing reaction time. Such a process may formally be described by a zero-order reaction rate law. The teniperature dependence of the reaction rate shall follow the Arrhenius relationship. With these prerequisites the heat production rate of this reaction can be expressed ... 

Figure 6-3 Graphic representation of zero order reaction - rate of changes in C (current account) and S (savings account), respectively, in relation to amount C at a given time (C(t))...

The right-hand side in Eqs. (26) contain the zero-order reaction rates ... 

Thus, a zero order reaction rate is obtained. It is characterized by a rate of substrate breakdown or product formation which is independent of substrate concentration, i. e. the reaction rate, V, is... 

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