Reproducibility, rate data

Reduction of CIOJ by citrate, tartrate and EDTA complexes of Fe(II) and by Cu(NH3)4 has been examined polarographically. All four reactions are first-order in reductant and C102. The data for the citrate and tartrate complexes were not reproducible but estimates of k2 (27 °C) were obtained. The rate data are... 

Steady state measurements of NO decomposition in the absence of CO under potentiostatic conditions gave the expected result, namely rapid self-poisoning of the system by chemisorbed oxygen addition of CO resulted immediately in a finite reaction rate which varied reversibly and reproducibly with changes in catalyst potential (Vwr) and reactant partial pressures. Figure 1 shows steady state (potentiostatic) rate data for CO2, N2 and N2O production as a function of Vwr at 621 K for a constant inlet pressures (P no, P co) of NO and CO of 0.75 k Pa. Also shown is the Vwr dependence of N2 selectivity where the latter quantity is defined as... 

The viscosity vs. shear rate data for PTF and BTF (Figure 9) were obtained in n-heptane solution at 25°C using a Contraves low shear rate instrument. n-Heptane was used as a nonpolar solvent, as it has a high enough boiling point to avoid losses due to evaporation during the measurement period. The curves presented here are reproducible in both directions of shear and are thus t ime-independent. 

To obtain reproducible kinetic data, Reiksfel d had to add styrene to a solution of [PhCH=CH2PtCl2]2 before MeCl2SiH was added. When the silane was added first and styrene was withheld for about 10 minutes, the rate of hydrosilation was noticeably retarded. 

One should be aware that the rate data are especially prone to variation. We have already seen that 1-alkenes are hydroformylated at a much higher rate, but at the same time they are rapidly isomerised to the much less reactive internal alkenes. This together with the highly exothermic reaction may result in low reproducibility. The results will thus strongly depend on the experimental procedures and how carefully they were executed. 

Fig. 29. Evaporation rate data for several low-volatility species in Nj measured by Tallin et al. (1988) by levitating microdroplets in an electrodynamic balance. From Measurement of Droplet Interfacial Phenomena by Light-Scattering Techniques, by Daniel C. TafBin, S. FI. Zhang, Theresa Allen and E. James Davis, A/CIiE Journo/, 34, No. 8, pp. 1310-1320, reproduced by permission of the American Institute of Chemical Engineers 1988 AIChE.

Ionic polymerizations, especially cationic polymerizations, are not as well understood as radical polymerizations because of experimental difficulties involved in their study. The nature of the reaction media in ionic polymerizations is often not clear since heterogeneous inorganic initiators are often involved. Further, it is extremely difficult in most instances to obtain reproducible kinetic data because ionic polymerizations proceed at very rapid rates and are extremely sensitive to the presence of small concentrations of impurities and other adventitious materials. The rates of ionic polymerizations are usually greater than those of radical polymerizations. These comments generally apply more to cationic than anionic polymerizations. Anionic systems are more reproducible because the reaction components are better defined and more easily purified. 

In view of these difficulties, as well as that of obtaining hydrocarbons of reproducible purity, we consider that the published over-all rate studies on mixtures of hydrocarbons are useful empirical observations, but that most quantitative treatments, including calculation of < values, are not yet really useful. We therefore endorse the statement by Allen and Plesch (6) on < values in copolymerization It would be. . . appropriate to point out that most of the simplifying assumptions, plausible enough in their context, made in polymer kinetics come home to roost in the factor. Therefore we omit our own rate data they are consistent with those already published (1, 2, 3, 4, 8, 30, 31, 32, 33). 

Slurry Viscosities. In addition to the yield stress, the characteristic shear stress-shear rate relation of the fuel slurry should be known since the shape of the shear rate-shear stress curve (consistency curve) is an indication of the gel characteristics. Low shear rate data (102 sec."1) are useful mainly in determining batch-to-batch reproducibility, while high shear rate data (104 to 106 sec."1) are required to assess the flow characteristics in engine hardware. 

Benzene alkylation with ethene was studied over HY, LaY, and SK-500 between 488° and 599°K and for C6 C2 from 0.7 to 10. Ethylbenzene ethylation was also studied. For propene alkylation, conditions were similar except that the temperature range was 350° to 493°K, and the study was less complete than for the ethene system. The experimental rate data typically exhibited a maximum with respect to time and underwent extended decay (Figure 1). The location of the peak is a function of reaction conditions, particularly temperature. The propene system deactivated more rapidly than the ethene system. Data for the ethene system were reproducible to 10%. 

Materials. Palladium acetate was prepared by oxidizing palladium black in acetic acid by 02 or by nitric acid (20). Material from nitric acid oxidation was crystallized five times or more before use, or more often, was purified by the following procedure. Finely powdered palladium acetate was made into a paste with sulfuric acid and digested at 140°-150°C for 30 min. Palladium (II) was thus converted into palladium sulfate, and crucial impurities were destroyed. Palladium sulfate was dissolved in water. After the sulfuric acid was neutralized, the addition of excess acetic acid precipitated purified palladium acetate. Oxi-dizable impurities were removed from acetic acid by repeated fractionation from CrOa and KMn04 solutions. Olefins were treated with alumina before use to remove peroxides. The reproducibility of the rate data was used as a test of the purity of reagents since the results were erratic when inadequate precautions had been taken. 

C/min) divided by the flow rate (F ml/min). Because of this, it may be hard to reproduce retention data in temperature programmed GC exactly, because whereas it may be possible to accurately control the heating rate, it may be more difficult to reproduce the flow rate F within 0.5%. 

HPLC on a 2.1mm column at 400 til min-1 flow. Two drugs are monitored by selected ion monitoring. Left 400 pi min-1 is injected in the source. Centre 132 almin-1 is split to the source. Right 15 pi min-1 is split to the source. The integration values are displayed on top of the peaks and show that at reduced flow rates the sensitivity is slightly increased. Reproduced with data from Covey T., Analytical Characteristics of the Electrspray Ionization Process pp. 21-59 in Biochemical and Biotechnological Applications of Eletrospray Ionization Mass Spectrometry Snyder A.P., ed., ACS Symposium Series 619, American Chemical Society, 1996. 

The reader will observe that the discussion of the empirical description of kinetic systems in the preceding section was resolved by a verbal sleight of hand. Whereas the raw kinetic data are usually in the form of concentrations of chemical components at given times (and indeed our aim is to reproduce such data by mathematical equations that represent these concentrations as functions of the time), our very first statement involved an entirely different language, that of the concentration derivatives (the rates of reaction) and their relations to concentrations. 

The generalized EE model fits conversion rate data for propane, n-butane, and n-hexane within the reproducibility of separate sets of data. The conversion range covered is from 10% or less to 99% or more. 

Several years ago Noxon et al. [23] first observed NO3 radicals in the atmosphere by means of its absorption at 662 nm of lunar light. Many subsequent measurements [24, 25] have been made and the general conclusion can be drawn that the observed atmospheric concentrations of NO3 are not accurately reproduced by attempts to model its chemistry with the available reaction rate data. This conclusion has stimulated a great deal of interest and activity involving NO3 chemistry. 

Photon spectroscopy associates two numbers with the pair of states involved in a transition, the energy-level difference and the transition rate. The correlated emission directions of photons in successive transitions are determined trivially by the dipole selection rule. In most cases it is impossible to solve the many-body problem accurately enough to reproduce spectroscopic data within experimental error and we are left wondering how good our theoretical methods really are. 

All the radicals in the system are good chain carriers, and propagation processes should be fast. It should also be noted that extensive wall conditioning was required before the rate data were reproducible. This is a characteristic of long chain processes. 

FIGURE 4.39. Comparison of the dependence of the surface fluoride cocnentration ([SiF], M) and the etch rate on the NH4F concentration (M) in the Si02-H20-HCI-NH4F-NH4Cl system etch rate data from Judge.- After Osseo-Asare. (Reproduced by permission of The Electrochemical Society, Inc.)... 

Methods. Using an Agla microsyringe, alkyl alcohol solution (0.025 ml) was spread on the subsolution of 0.01 M HC1. A time interval of 5 minutes was allowed for spreading solvents to evaporate or diffuse in the subsolution from the monolayers. The monolayer was compressed at a constant rate by an electrically operated motor. The surface pressure area curve for a monolayer was recorded automatically by x-y recorder. Three to five mono-layers of each mixture were studied and the results reported are average values. The reproducibility of data was + 0.15 8 /molecule. The detailed discussion of the apparatus is given elsewhere (17). 

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