Reaction rate constant, measurement

McFarland M, Albritton D L, Fehsenfeld F C, Ferguson E E and Schmeltekopf A L 1973 Flow-drift technique for ion mobility and ion-molecule reaction rate constant measurements. I. Apparatus and mobility measurements J. Chem. Phys. 59 6610-19... 

The results reflected by the data in Table 12.5 are similar to those on the crystal-growth kinetics of Na2HP04, />., the values for the reaction rate constant measured in the SCISR, Ais, are systematically higher than those measured in the STR, kSJ, by about 20%. 

An additional information relates to the microviscosity of the PP solutions. Their macroscopic viscosity is very high. However, the Ps reaction rate constant measured above Rc0 is only slightly lower than what it is in water on a microscopic scale, the diffusive properties of Ps inside the net created in the PP solution by the polymeric chains are similar to those in neat water... 

Albritton D.L., Ion-neutral reaction rate constants measured in flow reactors through 1977. In Atomic Data and Nuclear Tables , Vol. 22, No. 1. New York, Academic Press, 1978. 

Error limits on the rate constants are estimated as follows. The reproducibility of the rate constants is typically <10%. Sources of error include the above reproducibility ( 10%), measurement of temperature ( 2%), pressure ( 1%), ion flight time ( 5%), an end correction related mainly to reactant gas mixing ( 2 cm or 4%), buffer gas flow rate (relative, 1%, or absolute, 2%), and neutral reactant gas flow rate (relative, 3%, or absolute, 15%). Propagation of errors leads to a net relative uncertainty of 13% and a net absolute uncertainty of 19%. The reaction rate constants measured with the HTFA apparatus are quoted with relative and absolute uncertainties of 15% and 25%, respectively, to account for the possibility of systematic errors not treated in the above analysis. 

F. C. Fehsenfeld, A. L. Schmeltekopf, D. M. Dunkin, and E. E. Ferguson, Compilation of Reaction Rate Constants Measured in the ESSA Flowing Afterglow System to August, 1969, ESSA Technical Report ERL 135-AL3 (September 1969), U.S. Gov t. Priniting Office. 

Such advantages have motivated some to use IMS instruments for elementary studies such as ion/molecule association and displacement reactions, where results for standard enthalpy and entropy measurements are found to be in excellent agreement with those obtained by more usual methods. Reaction rate constant measurements for association and displacement reactions have been determined and, in the case of the displacement of Br from CHjBr by Cl an effect of pressure on the rate constant has been observed. Electron association and detachment reactions are studied more easily in an ambient pressure ion mobility spectrometer than the more conventional swarm-beam method and we suggest that this will be the method of choice in future studies. 

The flowing afterglow technique for ion-molecule reaction rate constant measurements has been developed since 1963 in the NOAA laboratories in Boulder, Colorado by A. L. Schmeltekopf, F. C. Fehsenfeld, and the author. This technique has also been applied recently to ion-molecule reaction studies in the laboratories of H. I. Schiff at York University, Toronto, W. L. Fite and F. Kaufman at Pittsburgh University, N. D. Twiddy at York University, England, " and perhaps elsewhere, so that extended results from this technique are to be expected in the future. 

The form of kinetic equation has been established, based on die reaction rate constant for each individual series of experiments (the relationship between the acid number and time), assuming various power functions (reaction order). The magnitude of the spread of the reaction rate constant, measured in a few experiments conducted in constant temperature using varying starting molar ratios of alcohol to methacrylic acid, was used as a criterion in a selection of a correct form of the kinetic equation. The range should not exceed a few per cent. As it turned out, such a discriminate approach, a classical one fixim the kinetics point of view, worked very well and allowed for a precise establishment of a kinetic equation. 

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