Laboratory kinetic measurements

The kinetic studies of Morse and Berner (197 ) suggest that the rate of calcite dissolution varies exponentially with the carbonate ion content undersat iration (see Fig. 5). They also suggest that the rate depends strongly on the phosphate content of the sea water. For the typical phosphate content of deep sea water (i.e. 2.0+0.05 ym/kg) their rates follow the equation  

Although these calculations predict that short term experiments will lead to somewhat lower equilibrium carbonate ion 

In defence of his solubility results Berner makes two arguments with which we would like to take issue. First he states that since he calculated the solubility of calc it e in sea water from measurements of the solubility of aragonite in sea water and the ratio of the solubility of calcite to aragonite as measured in fresh water that he avoids the serious kinetic effects associated with calcite in sea water. Whereas we do not challenge the legitimacy of Berner s approach, we do challenge his contention that direct measurements of the solubility of calcite in sea water cannot be made because of kinetic effects which are not shared by aragonite. In this connection we make four observations. 

Second, Berner uses the argument that his solubility for calcite is consistent with that calculated from the true thermodynamic constant whereas the value of Ingle et al. is not. The relationship between these constants is as follows  

and = the activity product for calcite, and the first and second dissociation constants for carbonic acid in infinitely dilute aqueous solutions. 

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Laboratory kinetic measurements have shown that the reactions of DMS with halogen oxide radicals, specially IO, and probably to a much lesser extent CIO and BrO, are potentially important in the DMS oxidation in the marine atmosphere. Tne reaction of DMS with IO could explain the lower values of the DMS lifetime obtained from different field measurements. These values range from fractions of a hour to approximately 40 hours. The present paper successively reports on these field measurements, the laboratory kinetic data obtained for the reaction of DMS with IO,... 

The coupling of photochemistry and physical mixing in a model is a challenging task for three reasons. First, the photochemical production and decomposition rates, as well as the dark decay rates of Interest, are often poor estimates. This Is both because of the lack of good laboratory kinetic measurements and because the light attenuation models Into which such measurements are Incorporated are subject to additional uncertainties. Second, the one-dlmenslonal mixing models make certain assumptions and... 

General guidelines concerning the choice of the most proper reactor type for the particular system to study, modified after Mills et al. (1992) are given in Table 5.4-10. The types, applications, advantages, and disadvantages of several laboratory reactors for kinetic measurements are given in Table 5.4-11. 

UV/visible spectroscopy of organometallic transients has been extremely important for kinetic measurements on previously identified species, but the spectra are less valuable for structural identification since most spectra show broad and featureless bands. One way round this problem has been to utilise matrix IR spectroscopy for characterisation and to use the data obtained from the matrix UV/visible spectrum to monitor the room-temperature kinetics. A more satisfactory method is to record the IR spectra of transients directly and there has been much activity in both gas phase and solution organometallic chemistry this field has been recently reviewed ( 35). In our laboratory,... 

Frostad, S., Klein, B., Lawrence, R.W. 2002. Evaluation of laboratory kinetic test methods for measuring rates of weathering. Mine Water and the Environment, 21, 183-192. 

Recently, the steady-state reaction kinetics of CO oxidation at high pressure over Ru , Rh " , Pt, Pd, and Ir single crystals have been studied in our laboratory. These studies have convincingly demonstrated the applicability and advantages of model single crystal studies, which combine UHV surface analysis techniques with high pressure kinetic measurements, in the elucidation of reaction mechanisms over supported catalysts. 

Kinetics measurements. When detailed literature data are not available and when one badly needs accurate kinetics, then the only recourse is to obtain kinetic data in the laboratory. 

As noted by Carberry in 1987, only phenomenological values can be measured in the laboratory since it is not possible to a priori distinguish between A (the catalytic area) and A (exposed measurable area), per volume of catalyst agent. This yields a structure-sensitive reaction that is dependent on crystallite size. While it is clear that a mechanism cannot be determined from purely kinetic measurements, a proposed mechanism is only accepted after it can predict the observed kinetic measurements. The dominant issue of the observed measurements is whether A or A is being measured. This correct measurement will yield the proper intrinsic kinetics, but will not reveal much insight into the mechanism. Thus, it is imperative to identify and obtain as much information as possible on the nature of intermediate chemical species. 

There are little data available which can be used to predict the rates of uptake of the different vaporized radioactive elements or oxides. Since such data are important to the application of any fallout prediction model based on kinetics, a program has been started at this laboratory to measure the rates of uptake of a selected group of fission-product oxides under conditions approximating those found in the cooling fireball. The data from these measurements will be useful, not only as input to fallout models, but also for discovering the mechanisms which govern the rates of uptake. 

Near-Infrared Chemiluminescence. The technique of chemiluminescence has been most successfully applied in the atmosphere to the measurement of NO and other oxides of nitrogen through various conversion procedures. Glaschick-Schimpf et al. (115) and Holstein et al. (116) reported results of laboratory kinetic studies in which the H02 concentration was determined through the chemiluminescence reaction system shown in equations 28 and 29. It involves the same molecular transitions in the near-infrared as discussed previously (for H02 emission from the 2A state). 

Fluorescence measurements of HO have been a common feature of laboratory kinetics studies of the reaction-rate coefficients of HO with various molecules and of studies of this free radical in combustion systems (24). In fact, although direct tropospheric fluorescence HO measurements were first... 

To preface the presentation of factors affecting kinetics measurements by time-resolved mass spectrometry in the next section, it is useful to see how a typical experimental setup would be configured. The following is a description of the apparatus originally designed and built in the author s laboratory at the University of Minnesota by S. B. Moore [35], and subsequently modified and improved, primarily by Fuxiang Wu. 

Other laboratory techniques applied to heterogeneous kinetics measurements are the entrained aerosol flow tube [73,76,77], the aerosol chamber technique [78] and the liquid flow jet [79]. 

Hammes (4S6) has summarized some of the extensive studies from his laboratory on the interaction of a variety of nucleotides with RNase-A as seen by relaxation kinetic measurements. The bimolecular and isomerization steps that occur with each of the nucleotides are very much faster than the rate determining steps separating the different substances. Thus the kinetic parameters for the interaction of each nucleotide can be established separately and then combined with steady state kinetic data to provide a detailed kinetic picture. The bimolecular steps are recognized by the concentration dependence of the relaxation time and the isomerization steps by the lack of a concentration dependence. 

Fluorescence microspectrophotometry typically provides chemical information in three modes spectral characterization, constituent mapping in specimens, and kinetic measurements of enzyme systems or photobleaching. All three approaches assist in defining chemical composition and properties in situ and one or all may be incorporated into modem instruments. Software control of monochrometers allows precise analysis of absoiption and/or fluorescence emission characteristics in foods, and routine detailed spectral analysis of large numbers of food elements (e.g., cells, fibers, fat droplets, protein bodies, crystals, etc.) is accomplished easily. The limit to the number of applications is really only that which is imposed by the imagination - there are quite incredible numbers of reagents which are capable of selective fluorescence tagging of food components, and their application is as diverse as the variety of problems in the research laboratory. 

Recently, we have carried out studies on the free radical chemistry of sulfite. These studies have included kinetic measurements on the reactions of organic and inorganic free radicals with sulfite and bisulfite, and on the reactions of the sulfite derived radicals SO and S0 with organic and inorganic substrates. In this paper, I will review some of our results and results from other laboratories on the radical chemistry of sulfite and discuss these results in relation to the problem of S02 autoxidation. 

FIG. 10 (a) Slow hematite aggregation kinetics measured in the laboratory... 

Corresponding to the different use of the criteria, a subdivision into two groups appears to be useful. Experimental criteria are needed when the kinetics of the reaction under consideration are still unknown, i.e. neither the type of rate law nor the intrinsic values of the kinetic parameters have yet been identified. This may be the case during an early stage of a laboratory kinetic study when a new reaction is analyzed for the first time. Experimental criteria in general contain only directly observable quantities, i.e. the measured effective rate of reaction as well as some (effective) physical properties of the catalyst and the reaction mixture (R, Z>c, Ac, etc.). Therefore, these can be easily applied. However, experimental criteria suffer from the disadvantage to be sometimes less conservative when more complex kinetics prevail. 

When the catalyst is available in a small amount, a microreactor assembly is often used (Miller, 1987). This is a simple T-type reactor heated by a fluidized sand bath. The mixing is provided by mechanical agitation that shakes the reactor up and down within the fluidized bed. Because of the small amount of slurry, and an effective heat transfer in the fluidized sand bath, the heat-up period in such a reactor is small. The nature of mechanical agitation is, however, energy-efficient. The reactor provides only a small sample for the product analysis, which makes the usefulness of the reactor for detailed kinetic measurements somewhat limited. The reactor has been extensively used for laboratory catalyst screening tests in coal liquefaction. 

Detailed kinetic measurements of the initial rates of iron uptake by rat liver mitochondria have been carried out in this laboratory during the last few years using 59Fe(III)-sucrose as the donor complex (23, 24, 27-32). The general features given in Table II support the concept that iron, like other cations, is accumulated by an energy-dependent as well as an energy-independent mechanism, and these two processes have different time, pH, and temperature dependencies. 

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