Calculation Of Reaction Rate Constants Research Articles

Pyrolysis and microwaves

The historic background, 1750–1950, of pyrolysis is sketched. At the end of this period the role of pressure, temperature and reaction vessel surface had been clarified. The use of a standard Stark-modulated microwave spectrometer (18–40 GHz) as the detector for polar products of pyrolysis at 0.001–0.01 mm Hg is described and examples given. The gap between theories for calculation of reaction rate constants and experimental results obtained by closed-vessel pyrolysis is still too large, presently leaving us with the production of new species as the most worthwhile results.

EVOLUTION DE L’UREE PLACEE EN BANDES DANS DEUX SOLS ACIDES DU QUEBEC

The objectives of this experiment were to determine the power of Morin (sand) and Achigan (sandy-loam) soils to hydrolyze urea and to nitrify ammonium. The urea was applied at a rate of 1500 mg N/kg soil in a drill 6 cm below the soil surface. The soils were incubated for 63 days at 20 °C and 25% moisture content (vol/wt) in 2-L containers. The band-applied urea hydrolysis was directly proportional to the logarithm of its remaining concentration in the soil (i.e. first-order reaction). Calculated reaction rate constants were −0.112 and −0.143 per day for the sand and the sandy loam, respectively. The unequal reaction rates were, presumably, related to the different chemical and physical properties of these soils. The rate of urea ammonification was significantly more rapid than the ammonium nitrification. One week after starting the incubation, only 18.3% and 11.5% of the applied urea remained in the Morin and Achigan soils, respectively. However, no nitrification was detected until about the 20th day and it was more active in the sandy soil. Soil pH increased and decreased significantly as ammonification or nitrification progressed, respectively.

Trajectory study of O+H2 reactions on fitted a b i n i t i o surfaces I: Triplet case

Classical trajectory calculations of cross sections for the reaction 0(3P)+H2(1Σ+g; ν, j) →OH(2Π; ν′, j′)+H(2S) have been performed for collision energies 1 kcal/mol⩽E⩽40 kcal/mol using an analytical fit to a recent ab inito potential energy surface. Three initial vibrational states of H2, ν=0, 1, and 2, are considered in order to study the influence of vibrational reactant energy on the OH production. With increasing vibrational quantum number, (a) the threshold shifts to lower energies, and (b) the cross sections rise more steeply with collision energy. Rotational excitation of H2 enhances the total reaction cross section for each vibrational state over the range of H2(ν,j) states studied. The cross sections have been used to calculate reaction rate constants for temperatures 300°K⩽T⩽1000°K and the three lowest vibrational states. The ratio k (T,ν=0):k (T,ν=1):k (T,ν=2) is found to be 1:1.13×104:1.42×106 at 300°K and 1:2.12×101:1.24×102 at 1000°K, demonstrating that vibrational energy strongly enhances the reaction rate. At low temperatures, T≲500°K, the calculated rate constants for ν=0 are considerably smaller than the experimental results indicating that the barrier in the potential surface is probably too high. Agreement with experiments is improved for intermediate temperatures and is best for T≳1500°K where threshold effects are least important. The present calculations are in very good agreement with a recent rate measurement at T∼302°K by Light for reactions of vibrationally excited H2(ν=1) molecules.

Collision Theory Approach to I'+HI→I'H+I Reaction

The impact-parameter method is applied to the hydrogen transfer reaction which has a similarity to resonant charge-transfer processes, due to the fact that mass ratio of H and I is fairly small. The cases for the four combinations (with or without taking account of the momentum transfer; either rectilinear and or curvilinear trajectories) are studied and compared. A (6-12) Lennard-Jones type potential is assumed to determine the curvilinear trajectory of the incident particle. A binding potential between H and I is assumed to be a Morse type. The calculated total cross section shows an undulating structure as a function of the incident velocity, similar to the glory effect, which is discussed in detail. The calculated reaction rate constants at room temperature are about 7×10 12 cc mol -1 sec -1 in the four cases. From our calculation, it appears that the momentum transfer effect is important and that the important contribution to the reaction rate comes from the cases where three atoms are in the collisi...

Reactions of amines with epoxy group. III. Calculation of reaction rate constants of aromatic diamines with p-tolyl glycidyl ether

Reactions of amines with epoxy group. III. Calculation of reaction rate constants of aromatic diamines with p-tolyl glycidyl ether

Calculation of reaction rate constants in ammonia synthesis over a reversibly steam-poisoned catalyst in continuous flow reactors

Calculation of reaction rate constants in ammonia synthesis over a reversibly steam-poisoned catalyst in continuous flow reactors

Method of calculating reaction rate constants from the structure of the reacting molecules

1. It is shown that it is possible to use an additive scheme of calculation to express the relation between the structure of a molecule and its reactivity, considering only the geometry of the molecule, the types of bonds and their position with respect to the reaction center. 2. An empirical formula is given for calculating reaction rate constants from the structural formulas of the reacting molecules.

Improved Method of Calculating Reaction Rate Constants for Free Radicals

Improved Method of Calculating Reaction Rate Constants for Free Radicals