Order with respect to concentration

For example, at 480°C the gaseous decomposition of acetaldehyde has an order with respect to concentration of 3/2. The main reaction is CH3CHO = CH4 +CO... 

A reaction order determined by the methods shown in Tables 2-1 and 2-2 and Fig. 2-5 is called an order with respect to concentration. ... 

The initial rate method yields the reaction order with respect to concentration. 

The rate of a second-order reaction may be proportional to two concentrations, v = [A][B] with [B]0 s> [A]o it follows first-order kinetics. Some authors refer to these as the order with respect to concentration and the order with respect to time. 

Although not very commonly used (with the exception of the initial rate procedure for slow reactions), the differential method has the advantage that it makes no assumption about what the reaction order might be (note the contrast with the method of integration, Section 3.3.2), and it allows a clear distinction between the order with respect to concentration and order with respect to time. However, the rate constant is obtained from an intercept by this method and will, therefore, have a relatively high associated error. The initial rates method also has the drawback that it may miss the effect of products on the global kinetics of the process. 

Indeed, catalysis of the water gas shift reaction is observed using (I) dissolved in methanol (50 ml) and water (25 ml) as catalyst in a 300 mL bomb at 100°C and with pressures of CO from 80-160 psi. Under these conditions the rate of reaction is independent of CO pressure and first order with respect to concentration of catalyst (I), giving a turnover rate of 3.6 0.6 (moles C02 or H2)/(mole catalyst)(hour). Good linear kinetics are observed for at least one day and solutions remain homogeneous... 

The rate of release of Mn from a Mn(III/IV) oxide is a function of the concentration of reductant in solution and oxide. The data in Fig. 7-5 and 7-6 show that with increasing concentrations of oxide or p-methylphenol the rate of release of Mn increases. With sufficient time the rate plots are curved (Fig. 7-6) due to the consumption of Mn oxide, because the reductant was in excess (Stone, 1987). At lower reductant concentrations the reaction is first-order with respect to concentration of reductant added (Stone and Morgan, 1984 Stone, 1987). The reduction is pH dependent with the rate increasing at lower pH. This is not surprising because reduction reactions consume protons and the adsorption of ligands is pH dependent. 

The number of nuclei reacting in a specified way with neutrons in unit time is proportional to the number of nuclei present and to the concentration of neutrons. In the language of chemical kinetics, neutron reactions are first-order with respect to concentration of nuclei and neutrons, and it is because neutron reactions are simple first-order Irreversible processes that a very detailed quantitative treatment of the rate processes in a nuclear reactor can be given. 

In the second method, slopes are measured only at the very beginning of the reaction, and the reaction is run at various initial concentrations. This type of procedure is represented schematically in Figure 9.6. The order, determined by plotting logiov(initial) against iogio a, is now known as the order with respect to concentration, since it is now the concentration that is varied. This order has been called the true... 

The hydrogenation of methoxybenzenes was found to be first order with respect to hydrogen pressure, zero order with respect to concentration of hydrogen acceptor, and directly proportional to the weight of catalyst used. The reaction rate is given by (4) ... 

In 1980, Baldea and Munteano" investigated the kinetics of the reaction between chromate and ascorbic acid. They found that the reaction was first order with respect to both ascorbate and chromate and 0.7 order with respect to concentration. We have... 

This is the simple Smoluchowski equation of orthokinetic flocculation, and shows that the rate of flocculation is second-order with respect to concentration, depends linearly on the velocity gradient and is proportional to the third power of the collision radius. Consequently, in these simple terms theory states that the rate of flocculation can be increased by ... 

It has to be pointed out that the heat of adsorption of NO (See ka4, Table 1) as reported by Oh and Cavendish (1981) has the wrong sign. Moreover, the dependence of F(x) in terms of T seems to be suspect. If the reactions are second-order with respect to concentrations, then should appear. This suggests that the rate expressions are not based on a clear mechanism, and that they should be considered semiempirical. They only fit well the experimental data of the authors. Finally, these rate expressions are valid at atmospheric pressure, an extrapolation to higher pressures could be questionable. 

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