Specific Reaction Rate Constants Research Articles

High‐Temperature Reaction Rates of Several Metals with Hydrogen Chloride and Water Vapor

An experimental study has been made of the high‐temperature reaction rates of various metal filaments with and vapors and mixtures of the two. Measurements were made by an electrical method in which the change in resistance of the metal filament was related to the loss in pure metal due to the vapor‐metal reaction. Measurable reaction rates were determined for both nickel and iron in a temperature range from 1000° to 1600°K. Specific reaction rate constants and apparent activation energies are presented. The reaction rates of tungsten with vapor were measured in a temperature range from 1600° to 2000°K. The reaction rates of chromium, Inconel, stainless, steel 18‐8, and tungsten did not proceed at a measurable rate in either pure or in mixtures of and . Nickel, copper, Inconel, and stainless steel 18‐8 did not react appreciably with water vapor at temperatures approaching the melting points. The reaction rates for iron in pure varied from 0.03 to 0.04% area loss per second over the temperature range investigated with an apparent activation energy of 10.5 kcal/mole. The reaction rates of iron in mixtures of and varied from 0.08 to 0.17% area loss per second in the same temperature range with an apparent activation energy of 8.5 kcal/mole. Reaction rates of nickel in pure varied from 0.005 to 0.03% area loss per second in the temperature range of 1000° to 1600°K with an apparent activation energy of 13 kcal/mole. The reaction rates of nickel in the and mixtures varied from 0.004 to 0.03% area loss per second in the same temperature range with an apparent activation energy of 22 kcal/mole below 1300°K and 13 kcal/mole above this temperature. Reaction rates of iron in vapor varied from 0.002 to 0.05% area loss per second from 1120° to 1415°K with an activation energy of 28 kcal/mole. Reaction rates of tungsten in vapor varied from 0.02 to 0.03% area loss per second from 1700° to 2000°K with an activation energy of 14.5 kcal/mole.

The Kinetics of the Disproportionation of Plutonium(V)1

A study has been made of the kinetics of the disproportionation of plutonium(V) in perchlorate solutions of unit ionic strength in which the PuC/sub 2//sup +/ was prepared by the reduction of the plutonyl ion with iodide ion. With this method of preparation, the disproportionation of plutonium(V) was studied in the absence of significant quantities of plutonium(II) and (IV) in the initial phases of the experiments. The rate of disproportionation of plutonium(V) has been found to be directly proportional to the first power of the hydrogen ion concentration which suggests that the slow step is probably PuO/sub 2//sup +/+ Pu(O)OH/sup ++/ yields PuO/sub 2//sup ++/ Pu(O)OH/sup +/. An activation energy of 19.6 kcal. has been computed from the temperature dependence of the specific reaction rate constants for the slow step of the disproportiomation reaction. The disproportionation of plutonium(V) has also been studied in deuterium oxide to note the influence of a change in solvent upon the reaction rates. It appears from the kinetic results obtained that no evidence has been foumd which would support the hydrogen atom transfer mechanism in the plutonium(V) disproportionation reaction. Plutonium(V) also has been prepared from the plutonyl ion by the spontaneous alpha -reduction process. Themore » kinetic data appear to be adequately described by a consideration of previously determined rate and equilibrium constants and the rate constant for the Pu(V)-- Pu(V reaction which was obtained from the experiments in which the plutonyl ion was reduced with iodide. (auth)« less

A polarographic investigation of the kinetics of epoxidation of unsaturated fatty acid esters

SummaryA polarographic technique which uses a nonaqueous electrolytic solution consisting of 0.25M ammonium acetate in glacial acetic acid is a suitable medium for the investigation of the kinetics of fatty acid ester epoxidations. From the polarographic data the specific reaction rate constants for the perlauric acid epoxidation of vinyl laurate, methyl oleate, and vinyl oleate in benzene at 25°C. were found to be 12, 232, and 270 × 10−3 l./mole−1 min−1. The Arrhenius equation for the epoxidations of methyl oleate and vinyl oleate by perlauric acid can be expressed as

The reaction of tobacco mosaic virus with formaldehyde: III. Kinetics of the Loss of Infectivity

The experiments reported here were designed to elucidate the nature of the chemical group on tobacco mosaic virus nucleoprotein which causes the biological inactivation of the virus when it reacts with formaldehyde. The methods of chemical kinetics were used to determine the specific reaction rate constants for the inactivation of the virus by 2% formaldehyde at several pH values within the range 4.1 to 8.4 and at 30°, 35°, and 40°. The reaction rate was found to be only slightly pH dependent, indicating that the critical group does not dissociate within the pH range studied. The reaction did not vary with ionic strength. A plot of the Arrhenius equation for the velocity constants obtained at pH values of 5.3, 6.8, and 7.8 gave an energy of activation of 19,500 calories per mole, which is the approximate value found for a reaction involving a single chemical bond. The energy of activation was invariable with pH. The rate constant was dependent on formaldehyde concentration when 2% virus solutions were allowed to react with 1%, 2%, 4%, and 7% formaldehyde solutions at pH 6.6 and 30°. These results could be interpreted on the basis of the inactivation's being caused by the reaction of a single formaldehyde molecule at one site on the virus characteristic particle. Prior treatment of the virus nucleoprotein with iodine, diazotized sulfanilic acid, acetic anhydride, and propionaldehyde failed to produce any effect on the rate constants for the subsequent formaldehyde inactivation process, indicating that the sulfhydryl, phenolic hydroxy, and protein amino groups are probably not the ones which cause the inactivation when they react with formaldehyde. Since changes in pH did not appreciably affect the rate constant value between pH 4.1 and pH 8.4, certain other groups can be eliminated from consideration on the basis of their pK values. Proton donor groups with pK values less than 9 and proton acceptor groups with pK values greater than about pK 3 to 4 can be excluded. The amide groups are probably not fundamentally involved, since they are reported to react more readily in acid medium. If this is true, then the inactivation rate constant would increase with increasing acidity, which is contrary to the results of this work. It has been shown by other investigators that tryptophan in tobacco mosaic virus probably does not react with formaldehyde in the pH range employed here. On the basis of the foregoing considerations, it is probable that the groups most likely involved in the formaldehyde inactivation of tobacco mosaic virus are the beta hydroxy groups of serine and threonine, the hydroxy group of ribose, and the amino group on the pyrimidine and purine rings in the nucleic acid.

On the Relationship between the Natural Electrode Potential and the Corrosion Rate (III)

The corrosion reaction of iron in acid solutions have been studied by means of chemical kinetics. The cathodes of local cells in iron are oxygen electrodes at higher pH than 4 and hydrogen electrodes at lower pH than 4. The corrosion ersistivity of metals K is related to the standard electrode potential EM0 and the specific reaction rate constant of hydrogen electrode K1 by the expression(This article is not displayable. Please see full text pdf.) \ oindentwhere n is the valency of metal ions. 1>α>0, T the absolute temperature and R and F are universal constants. There seems to be some relation between K and the work function of metals. The general Eq. of corrosion rate are as follows:(This article is not displayable. Please see full text pdf.) \ oindentwhere β is a constant of the anode film, β≥1, C is the concentration of adsorbed water molecule on metals, DM is the diffusion constant of metal ions and δm the thickness of diffusion layer.

Studies of onion root respiration IV. Kinetics of the respiratory overshoot

The respiratory overshoot and regular respiration of mitotically active and mature onion root segments have been measured at temperatures ranging from 15 to 43°C. The regular respiration is zero order, the overshoot respiration, of the first order. The rebound reaction seems to be composed of two different reactions, as indicated by the fact that two separate values are obtained for the specific reaction rate constants characterized by different temperature coefficients and by the fact that there is a marked overpayment of the anaerobically incurred oxygen debt. Maxima appear in the total amount of oxygen necessary for the removal of accumulated metabolites in the post-anaerobic reaction. These maxima seem to be a function both of the temperature of the respiring system and of the length of the anaerobic period.

Theoretical Considerations Concerning the Separation of Isotopes

The relative importance of effusion processes, the half quanta due to van der Waals forces, and half quanta associated with homopolar bonds is considered with respect to the question of the separation of isotopes. Specific reaction rate constants for various isotopic molecules in effusion processes have been calculated. It is shown that only in the neighborhood of liquid hydrogen temperatures or lower are the half quanta due to van der Waals forces important. Specific reaction rate constants involving the zero point energy of homopolar molecules have been calculated for various isotopic molecules, principally those in which a hydrogen atom is one constituent, at temperatures of 20°K, 90°K, and 273°K. The advantage of working at as low a temperature as possible is rendered apparent. Even at ordinary temperatures the differences in the constants are in general much greater than in the case of effusion or van der Waals processes. A general equation is derived relating the concentration of the light and heavy isotopes, valid for any one of the three processes considered.