Hydrogen peroxide coefficients

HO-oxidation of an individual NMHCj produces H02 radicals with a yield aj, and oxidation of the NMHC oxidation product produces H02 in stoichiometric amount The lumped coefficients or yields a and p need not be integers, and represent the effectiveness of a particular NMHCj in producing RO2. and H02 radicals (lumped together as HO2) that will then oxidize NO. to N02 in processes such as R6 and R13, producing one net ozone molecule each. Alternatively, when the NO. concentration is low, peroxyl radicals may form PAN (as in R22) or hydrogen peroxide (as in R33) which are other oxidant species. In this formulation, transport is expressed by an overall dilution rate of the polluted air mass into unpolluted air with a rate constant (units = reciprocal time dilution lifetime=1// ). This rate constant includes scavenging processes such as precipitation removal as well as mixing with clean air. 

It is worth mentioning that an attempt was made by Tsao and Willmarth to determine the acid dissociation constant of HO2. The reaction between hydrogen peroxide and peroxydisulphate was used for the generation of the HO2 radical. However, these experiments, like others where the HO2 radical is studied under steady-state conditions, could yield only a value of acidity constant multiplied by a coefficient consisting of a ratio of kinetic parameters. Unfortunately, in this case there are no independent data for the kinetic coefficient, and the value of cannot be evaluated. Considering the kinetic analogue of the titration curve it can be stated only that ionization of HO2 becomes important in the pH range from 4.5-6.5. The value of acidity constant of HO2 obtained by Czapski and Dorfman is (3.5 + 2.0)x 10 mole.l. . ... 

The oxidation of primary and secondary alcohols in the presence of 1-naphthylamine, 2-naphthylamine, or phenyl-1-naphthylamine is characterized by the high values of the inhibition coefficient / > 10 [1-7], Alkylperoxyl, a-ketoperoxyl radicals, and (3-hydroxyperoxyl radicals, like the peroxyl radicals derived from tertiary alcohols, appeared to be incapable of reducing the aminyl radicals formed from aromatic amines. For example, when the oxidation of tert-butanol is inhibited by 1-naphthylamine, the coefficient /is equal to 2, which coincides with the value found in the inhibited oxidation of alkanes [3], However, the addition of hydrogen peroxide to the tert-butanol getting oxidized helps to perform the cyclic chain termination mechanism (1-naphthylamine as the inhibitor, T = 393 K, cumyl peroxide as initiator, p02 = 98 kPa [8]). This is due to the participation of the formed hydroperoxyl radical in the chain termination ... 

Fig. 2. Rate coefficients for the low-pressure region of the unimolecular decomposition of hydrogen peroxide. A, Ref. 10 , ref. 15 O, refs. 16,17 (total density 10"2 mole.I-1) , refs. 16, 17 (total density 10 1 mole.l 1).

Pierotti, C., Deal, C., and Derr, E. Activity coefficient and molecular structure, Ind. Chem. Eng. Fundam., 51 95-101, 1959. Pignatello, J.J. Dark and photoassisted Fe -catalyzed degradation of chlorophenoxy herbicides by hydrogen peroxide. Environ. 

Die next parameter we need is the diffusion coefficient Df of hydrogen peroxide in water. Here, we can assume the approximate value of 10 9 m2/s. However, this coefficient will be needed further in this example for the determination of the effective solid-phase diffusion coefficient, in a calculation that is extremely sensitive to the value of the liquid-phase diffusion coefficient. For this reason, coefficient should be evaluated with as much accuracy as possible. The diffusion coefficient of solutes in dilute aqueous solutions can be evaluated using the Hayduk and Laudie equation (see eq. (1.26) in Appendix I) ... 

You can balance unbalanced equations by adding or changing coefficients to produce correct ratios. (It s important not to change subscripts, however, because to do so changes the compound s identity—H20 is water, but H202 is hydrogen peroxide ) For example, to balance the preceding equation, add a 3 before the NO ... 

The stoichiometric yield of OH0 is the greatest from the photolysis of hydrogen peroxide. But - as already mentioned - the photolysis of ozone yields more OH0 than that from hydrogen peroxide because of the higher molar extinction coefficient of ozone compared to hydrogen peroxide (see Table 2-3). 

Fig. 7. Absorption spectrum of hydrogen peroxide vapor. The absorption coefficient, a, is defined by the equation / = 70 exp (— atcd), where c is the concentration in molecules/cc. and d is the length of the light path in cm. Curve (a) and point O after Holt et al. (45,46). Curve (b) after Urey et al. (85). This figure based on refs. (46) and (85) with the permission of The Journal of Chemical Physics and the Journal of the American Chemical Society.

RATE COEFFICIENTS FOR THE REACTIONS OF BORONIC ACIDS WITH HYDROGEN PEROXIDE IN SOLVENT WATER AT 25 °C16... 

The experimental Tafel slope does not appear to deviate significantly from 120mV/decade, which corresponds to a transfer coefficient of 0.5, and this over the complete investigated range of hydrogen peroxide concentration and pH (Fig.4.6). This Tafel slope is found within a potential range restricted from ca. -0.10 to 0.20V vs. SCE. Above =0.20 V vs. SCE, the inclination of the current-potential curve appears to decrease. In Fig. 4.7,... 

If the experimental observations are summarised, a constant finding is the value of 0.5 for the transfer coefficient of the oxidation reaction, with all the combinations of hydrogen peroxide concentration and pH. Obviously, this is valid only in the potential range in which this transfer coefficient was experimentally determined. With potentials outside this range, the transfer coefficient cannot be used as a criterion. This value of the transfer coefficient is a primary requirement which every postulated reaction mechanism should meet theoretically. Furthermore, it is certain that hydroxide ions interfere in the oxidation reaction. 

Although the anodic term is dependent both on the hydrogen peroxide concentration and on the hydroxide ions concentration, the theoretically predicted value of the anodic transfer coefficient, i.e. 1, is twice that at the experimentally observed value. Moreover, Equation 4.36 predicts that the anodic current depends on the concentration of dissolved oxygen, which is not observed experimentally. When k 2 k3 is assumed, this mechanism also should consequently be rejected. 

When k 3 k4" and/or k 2 k4" is assumed, the transfer coefficient of the anodic current corresponds to the one obtained experimentally. For the reaction orders of hydrogen peroxide and OH, a value of 1 is predicted. These orders, predicted by one of the postulated competing mechanisms, should not be compared to the experimentally obtained orders, which are also influenced by both the orders in the second sub-mechanism and by the other parameters in the rate equations concerned. Only the orders resulting from a combination of two not rejected mechanisms are to be compared with the experimentally obtained orders. Hence, mechanism 1 with substage 4 as RDS qualifies as a possible sub-mechanism in the complete wave. 

Under the condition k, " k5", the confrontation of the predicted consequences of the anodic term with the experimental evidence leads us to the conclusion that mechanism 1 of which stage 5 is the RDS cannot explain the experimental observations in the foot of the prewave because of the diverging transfer coefficient. Since with more positive potentials, the transfer coefficient cannot be used as a criterion, mechanism 1 with stage 5 as RDS should not be rejected with these potentials, because the predicted anodic current depends on the hydroxide ions concentration and the hydrogen peroxide concentration, as is experimentally observed. 

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