Non-equilibrium kinetics of bimolecular reactions. Part 6. Transient rate coefficients

1994 ◽  
Vol 72 (3) ◽  
pp. 714-720
Author(s):  
Chris Carruthers ◽  
Heshel Teitelbaum
Keyword(s):  
Population Distribution ◽  
Bimolecular Reaction ◽  
Rate Coefficients ◽  
Exchange Reactions ◽  
Equilibrium Conditions ◽  
Bimolecular Reactions ◽  
Wide Range ◽  
Vibrational Population ◽  
Kinetics Of ◽  
Non Equilibrium

The master equation is solved numerically for the time dependence of the vibrational level populations of HCl (treated as a simple harmonic oscillator) during the bimolecular exchange reaction, Br + HCl → HBr + Cl, taking into account the competition between reaction and vibrational equilibration subject to Landau–Teller T–V excitation. Strong deviations from Boltzmann distributions are found. A wide range of reactant concentrations, diluent concentrations and temperatures were explored. It was found that no significant reaction occurs before the establishment of a steady vibrational population distribution, confirming that the rate coefficient for non-equilibrium bimolecular exchange reactions can be determined from a simple analytical steady state treatment (J. Chem. Soc. Faraday Trans. 87, 229 (1991)). The rate of an isolated elementary bimolecular reaction, A + BC → AB + C, under non-equilibrium conditions can deviate seriously from the standard expression, Keq [A][BC], and is better given by the law[Formula: see text]where [R] is the concentration of the collisional equilibrator, R, and a and g are constants depending only on temperature. This generalized rate law describes not only the initial rate but also the rate all the way up to completion, in the absence of the reverse reaction.

scholarly journals The thermal decomposition of acetaldehyde and the existence of different activated states

1933 ◽  
Vol 141 (843) ◽  
pp. 41-55 ◽  
Keyword(s):  
High Pressures ◽  
Initial Pressure ◽  
Bimolecular Reaction ◽  
Bimolecular Reactions ◽  
First Order ◽  
Straight Line ◽  
Gas Reactions ◽  
Pass Through ◽  
Low Pressures ◽  
Kinetics Of

Homogeneous thermal gas reactions were at one time tacitly assumed to possess a definite order, unimolecular and bimolecular reactions, for example, being sharply distinguished. The kinetics of the decomposition of acetalde­ hyde, CH 3 CHO = CH 4 + CO, over the pressure range of 100 to 400 mm. were found to satisfy the criterion of a bimolecular reaction, namely, that the reciprocal of the time for half change (1/ t 1/2 ) )plotted against the initial pressure ( p 0 ) gave a straight line inclined to the axes. The line, however, did not pass through the origin, as may be seen in fig. 1 of the present paper. This indicated the presence of some first order reaction, the nature of which was not determined. Subsequently, in accordance with the collision theory of activation and deactivation, it was shown that certain reactions, sometimes called quasiummolecular, change their order from the second at low pressures to the first at high pressures. This apparently was the reverse of the behaviour shown by acetaldehyde.

scholarly journals Technical note: Entrainment-limited kinetics of bimolecular reactions in clouds

2021 ◽  
Author(s):  
Christopher D. Holmes
Keyword(s):  
Atmospheric Chemistry ◽  
Reaction Rates ◽  
Bimolecular Reaction ◽  
Technical Note ◽  
Cloud Chemistry ◽  
Bimolecular Reactions ◽  
Kinetic Rate ◽  
First Order Kinetics ◽  
Fractional Cloud ◽  
Kinetics Of

Abstract. The method of entrainment-limited kinetics enables atmospheric chemistry models that do not resolve clouds to simulate heterogeneous (surface and multiphase) cloud chemistry more accurately and efficiently than previous numerical methods. The method, which was previously described for reactions with first-order kinetics in clouds, incorporates cloud entrainment into the kinetic rate coefficient. This technical note shows how bimolecular reactions with second-order kinetics in clouds can also be treated with entrainment-limited kinetics, enabling efficient simulations of a wider range of cloud chemistry reactions. Accuracy is demonstrated using oxidation of SO2 to S(VI) – a key step in formation of acid rain – as an example. Over a large range of reaction rates, cloud fractions, and initial reactant concentrations, the numerical errors in the entrainment-limited bimolecular reaction rates are typically << 1 % and always < 4 %, which is far smaller than the errors found in several commonly used methods of simulating cloud chemistry with fractional cloud cover.

The Kinetics of Reactions in and Near the Cytochrome b/f Complex of Chloroplast Thylakoids. I. Proton Deposition

1988 ◽  
Vol 15 (5) ◽  
pp. 695 ◽  
Author(s):  
AB Hope ◽  
J Liggins ◽  
DB Matthews
Keyword(s):  
Rate Constant ◽  
Bimolecular Reaction ◽  
Plastoquinone Pool ◽  
Rate Limiting Step ◽  
Fixed Concentration ◽  
Wide Range ◽  
Entropy Of Activation ◽  
Electron Donation ◽  
Rate Limiting ◽  
Kinetics Of

The kinetics of proton deposition in the intrathylakoid spaces of pea chloroplasts were measured under a wide range of conditions. With duroquinol added to reduce the plastoquinone pool, and 3-(3,4-dichlorophenyl)-1,1-dimethylurea added to inhibit photosystem II, but no ionophore present, the proton deposition, attributed to plastoquinol oxidation, was biphasic. About half the deposition had an apparent rate constant (k) of 150-200 s-1, the other half about 10 s-1. Valinomycin or nonactin (<0.1 �M) plus potassium ions made the deposition almost monophasic, with k = 140 s-1. When the state of reduction of the plastoquinone pool was varied by the addition of varied concentrations of duroquinol, in the presence of 1 �M nonactin, k for proton deposition varied from about 20 (0.01 mM duroquinol) up to a maximum of 140 s-1 (0.5 mM duroquinol). When temperature was varied between 4 and 23°C, with 1 �M nonactin, an Arrhenius plot of ln(k) for proton deposition was linear; the activation enthalpy was 67 kJ mol-1, the entropy of activation, 23 J K-1 mol-1. The data are analysed in terms of a bimolecular reaction between a varying concentration of plastoquinol and a fixed concentration of oxidised Rieske centre. The results are consistent with a rate constant, for the first electron donation by plastoquinol, of 28 s-1 (the rate-limiting step), followed by a relatively fast second electron donation to cytochrome b563 (low potential), followed by deposition of two protons. The speed of the second proton deposition is dependent on the membrane potential difference.

scholarly journals Isotope exchange reactions involving HCO+ with CO: A theoretical approach

2017 ◽  
Vol 605 ◽  
pp. A22 ◽  
Author(s):  
M. Mladenović ◽  
E. Roueff
Keyword(s):  
Reaction Rate ◽  
Isotopic Exchange ◽  
Least Squares Method ◽  
Outer Space ◽  
Nonlinear Least Squares ◽  
Rate Coefficients ◽  
Exchange Reactions ◽  
Forward Reaction ◽  
Equilibrium Conditions ◽  
Nonlinear Least Squares Method

Aims. We aim to investigate fractionation reactions involved in the 12C/13C, 16O/18O, and 17O balance. Methods. Full-dimensional rovibrational calculations were used to compute numerically exact rovibrational energies and thermal equilibrium conditions to derive the reaction rate coefficients. A nonlinear least-squares method was employed to represent the rate coefficients by analytic functions. Results. New exothermicities are derived for 30 isotopic exchange reactions of HCO+ with CO. For each of the reactions, we provide the analytic three-parameter Arrhenius-Kooij formula for both the forward reaction and backward reaction rate coefficients, that can further be used in astrochemical kinetic models. Rotational constants derived here for the 17O containing forms of HCO+ may assist detection of these cations in outer space.

Kinetics of the unimolecular reaction of CH2OO and the bimolecular reactions with the water monomer, acetaldehyde and acetone under atmospheric conditions

2015 ◽  
Vol 17 (30) ◽  
pp. 19862-19873 ◽  
Author(s):  
Torsten Berndt ◽  
Ralf Kaethner ◽  
Jens Voigtländer ◽  
Frank Stratmann ◽  
Mark Pfeifle ◽  
...  
Keyword(s):  
Rate Coefficients ◽  
Unimolecular Reaction ◽  
Atmospheric Conditions ◽  
Bimolecular Reactions ◽  
Kinetics Of

The rate coefficients of the unimolecular reaction of CH2OO and the bimolecular reactions with the water monomer and carbonyls were measured.

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