2003 Alfred Bader Award LecturePredicting the rates of chemical reactions

2005 ◽  
Vol 83 (1) ◽  
pp. 1-8 ◽  
Author(s):  
J Peter Guthrie
Keyword(s):  
Computational Chemistry ◽  
Chemical Reactions ◽  
Chemical Reaction ◽  
Chemical Reactivity ◽  
Equilibrium Thermodynamics ◽  
Detailed Mechanism ◽  
Quantitative Tool

The dream of being able to predict the rate of a chemical reaction corresponding to a detailed mechanism is now almost within our grasp. No barrier theory (NBT), which makes the calculations relatively facile, is described, as are various applications of the approach to date. Illustrations are given of the use of NBT not just as a quantitative tool for predicting rates, but as a qualitative tool for thinking about which of a pair of reactions will have the higher intrinsic barrier, and thus be slower for similar thermodynamic driving force.Key words: rate, equilibrium, thermodynamics, kinetics, no barrier theory, computational chemistry, chemical reactivity.

scholarly journals Application of computational chemistry in chemical reactivity: a review

2021 ◽  
Author(s):  
C. W. Chidiebere ◽  
C. E. Duru ◽  
J. P. C. Mbagwu
Keyword(s):  
Computational Chemistry ◽  
Molecular Orbital ◽  
Chemical Reactions ◽  
Quantum Physics ◽  
Chemical Reactivity ◽  
Chemical Change ◽  
Molecular Orbitals ◽  
Automatic Data ◽  
Highest Occupied Molecular Orbital ◽  
Lowest Unoccupied Molecular Orbital

Molecular orbitals are vital to giving reasons several chemical reactions occur. Although, Fukui and coworkers were able to propose a postulate which shows that highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) is incredibly important in predicting chemical reactions. It should be kept in mind that this postulate could be a rigorous one therefore it requires an awfully serious attention in order to be understood. However, there has been an excellent breakthrough since the introduction of computational chemistry which is mostly used when a mathematical method is fully well built that it is automated for effectuation and intrinsically can predict chemical reactivity. At the cause of this review, we’ve reported on how HOMO and LUMO molecular orbitals may be employed in predicting a chemical change by the utilization of an automatic data processing (ADP) system through the utilization of quantum physics approximations.

scholarly journals On the law and mechanism of monomolecular reaction

1926 ◽  
Vol 110 (755) ◽  
pp. 543-560 ◽  
Keyword(s):  
Chemical Reactions ◽  
Chemical Reaction ◽  
Chemical Reactivity ◽  
Thermionic Emission ◽  
Black Body ◽  
Black Body Radiation ◽  
Single Frequency ◽  
Monomolecular Reaction ◽  
Wide Range ◽  
The Law

1. The object of the present paper is to work out an expression for the rate of monomolecular reaction on the basis of the idea that radiation is the cause of such reactions. The whole position of the radiation hypothesis of chemical reactivity up till now has been fully discussed by Harned. I only wish to draw attention to the fact, as pointed out by Langmuir, and Lewis and McKeown, that a great similarity exists between photo-electric emission of electrons and photo-chemical reaction. The true analogue of the thermo-chemical reaction should be sought, however, in the phenomenon of thermionic emission of electrons. It has long been shown experimentally by Richardson and others that the thermionic emission of electrons is vastly in excess of the total photo-electric emission at any temperature T. In the same way we should expect that the amount of thermo-chemical reaction in a system at a given temperature should be greater than the total photo-chemical reaction by black body radiation at the same temperature. Becker has shown that the distribution of velocities among the photo-electrons emitted from a metal by the action of black body radiation at a temperature T is similar to that found amongst the electrons emitted thermally from the hot metal at the same temperature T. It is thus natural to assume that the thermionic emission of electrons from a hot body is really due to the radiation in equilibrium with it. Richardson║ has recently given a very interesting discussion on the photo-electric theory of thermionic emission of electrons. Owing to the well-known difficulties the old view of the freely-moving electrons in a metal has, in recent years, been replaced by that of a lattice structure— a metal being considered to be constituted of interlaced lattices of ions and electrons. Such a view of metallic electrons precludes them from sharing in kinetic energy according to the equipartition law. It is rather more rational to imagine that the metallic electrons do exist in some modified quantum orbits, and are bound to the ions by a certain potential energy. If this view of the electronic structure in metals be accepted, then we have to look to radiation as the only controlling factor in the emission of electrons from hot bodies. The writer has tried to show that the law of thermionic emission derived on the basis of radiative mechanism is in good agreement with experiment. Lewis and McKeown have pointed out that “the concept of matter and radiation being at one and the same temperature means that as a result of absorption and emission, the system as a whole maintains a certain distribution of energy among all frequencies.” If by some process a set of frequencies are removed the system tends to make good the loss by a corresponding reverse process, provided the velocity of the process be not too large to make it physically impossible to keep the system at a fixed temperature by means of a thermostat. In my view the resemblance of photo-electric emission and photo-chemical reaction with thermionic emission and thermo-chemical reaction respectively arises from both kinds of processes being due to radiation. But the distinction lies in the fact that one is due to the action of high temperature radiation on a cold system, while the other is brought about by the action of radiation in temperature equilibrium with the system itself. 2. The Range of Frequencies of Radiation capable of bringing about a Chemical Reaction . Up till now it has been usually assumed that a single frequency, or rather a narrow range of frequencies, is capable of bringing about a chemical change. But experiments have shown that photo-chemical reactions are produced by the action of light of a wide range of frequencies. The simplest of all chemical reactions is the breaking up of atoms into ions and electrons, and it is widely known that the photo-electric action in various elements, both in solid and vapour phase, are brought about by all frequencies of radiation above a certain limiting frequency. The familiar reaction of practical photography is also known to be produced by light of a great variety of wave-lengths. It is, therefore, evident that a more complete theory of chemical reactivity should involve a summation of a number of frequencies, or, what is more plausible, an integration over a whole range of frequencies above a certain limiting value.

Normal approximations for distributions arising in the stochastic approach to chemical reaction kinetics

1981 ◽  
Vol 18 (01) ◽  
pp. 263-267 ◽  
Author(s):  
F. D. J. Dunstan ◽  
J. F. Reynolds
Keyword(s):  
Reaction Kinetics ◽  
Chemical Reactions ◽  
Chemical Reaction ◽  
Stochastic Approach ◽  
Algebraic Functions ◽  
Chemical Reaction Kinetics ◽  
Normal Approximations ◽  
Formal Solutions

Earlier stochastic analyses of chemical reactions have provided formal solutions which are unsuitable for most purposes in that they are expressed in terms of complex algebraic functions. Normal approximations are derived here for solutions to a variety of reactions. Using these, it is possible to investigate the level at which the classical deterministic solutions become inadequate. This is important in fields such as radioimmunoassay.

Epitaxy and Chemical Reactions During Thin Film Formation from Low Energy Ions New Kinetic Pathways, New Phases and New Properties

1991 ◽  
Vol 236 ◽  
Author(s):  
Nicole Herbots ◽  
O.C. Hellman ◽  
O. Vancauwenberghe
Keyword(s):  
Thin Film ◽  
Chemical Reactions ◽  
Degrees Of Freedom ◽  
Film Growth ◽  
Film Formation ◽  
Chemical Reactivity ◽  
Ion Beam ◽  
Low Energy ◽  
Low Energy Ions ◽  
Beam Deposition

AbstractThree important effects of low energy direct Ion Beam Deposition (IBD) are the athermal incorporation of material into a substrate, the enhancement of atomic mobility in the subsurface, and the modification of growth kinetics it creates. All lead to a significant lowering of the temperature necessary to induce epitaxial growth and chemical reactions. The fundamental understanding and new applications of low temperature kinetics induced by low energy ions in thin film growth and surface processing of semiconductors are reviewed. It is shown that the mechanism of IBD growth can be understood and computed quantitatively using a simple model including ion induced defect generation and sputtering, elastic recombination, thermal diffusion, chemical reactivity, and desorption The energy, temperature and dose dependence of growth rate, epitaxy, and chemical reaction during IBD is found to be controlled by the net recombination rate of interstitials at the surface in the case of epitaxy and unreacted films, and by the balance between ion beam decomposition and phase formation induced by ion beam generated defects in the case of compound thin films. Recent systematic experiments on the formation of oxides and nitrides on Si, Ge/Si(100), heteroepitaxial SixGe1−x/Si(100) and GaAs(100) illustrate applications of this mechanism using IBD in the form of Ion Beam Nitridation (IBN), Ion Beam Oxidation (IBO) and Combined Ion and Molecular beam Deposition (CIMD). It is shown that these techniques enable (1) the formation of conventional phases in conditions never used before, (2) the control and creation of properties via new degrees of freedom such as ion energy and lowered substrate temperatures, and (3) the formation of new metastable heterostructures that cannot be grown by pure thermal means.

scholarly journals Revising global ozone dry deposition estimates based on a new mechanistic parameterisation for air-sea exchange and the multi-year MACC composition reanalysis

2017 ◽  
Author(s):  
Ashok K. Luhar ◽  
Matthew T. Woodhouse ◽  
Ian E. Galbally
Keyword(s):  
Chemical Reaction ◽  
Dry Deposition ◽  
Tropospheric Ozone ◽  
Surface Resistance ◽  
Chemical Reactivity ◽  
Deposition Velocity ◽  
Water Layer ◽  
Turbulent Transfer ◽  
Dominant Term ◽  
Deposition Velocities

Abstract. Dry deposition at the Earth’s surface is an important sink of atmospheric ozone. Currently, dry deposition of ozone to the ocean surface in atmospheric chemistry models has the largest uncertainty compared to deposition to other surface types, with implications for global tropospheric ozone budget and associated radiative forcing. Most models assume that the dominant term of surface resistance in the parameterisation of ozone dry deposition velocity at the oceanic surface is constant. We present a consistent, process-based parameterisation scheme for air-sea exchange in which the surface resistance accounts for the simultaneous waterside processes of ozone solubility, molecular diffusion, turbulent transfer, and a first-order chemical reaction of ozone with dissolved iodide. The new scheme makes the following realistic assumptions: (a) the thickness of the top water layer is of the order of a reaction-diffusion length scale (a few micrometres) within which ozone loss is dominated by chemical reaction and the influence of waterside turbulent transfer is negligible; (b) in the water layer below, both chemical reaction and waterside turbulent transfer act together and are accounted for; and (c) iodide (hence chemical reactivity) is present through the depth of the oceanic mixing layer. The asymptotic behaviour of the new scheme is consistent with the known limits when either chemical reaction or turbulent transfer dominates. It has been incorporated into the ACCESS-UKCA global chemistry-climate model and the results are evaluated against dry deposition velocities from currently best available open-ocean measurements. In order to better quantify the global dry deposition loss and its interannual variability, the modelled 3-h ozone deposition velocities are combined with the 3-h MACC (Monitoring Atmospheric Composition and Climate) reanalysis ozone for the years 2003–2012. The resulting ozone dry deposition is found to be 98.4 ± 4.5 Tg O3 yr−1 for the ocean and 722.8 ± 20.9 O3 yr−1 globally. The new estimate of the ocean component is approximately a third of the current model estimates. This reduction corresponds to an approximately 20 % decrease in the total global ozone dry deposition, which is equivalent to an increase of approximately 5 % in the modelled tropospheric ozone burden and a similar increase in tropospheric ozone lifetime.

scholarly journals Mapping the Space of Chemical Reactions using Attention-Based Neural Networks

2020 ◽  
Author(s):  
Philippe Schwaller ◽  
Daniel Probst ◽  
Alain C. Vaucher ◽  
Vishnu H Nair ◽  
David Kreutter ◽  
...  
Keyword(s):  
Neural Networks ◽  
Reaction Center ◽  
Chemical Reactions ◽  
Chemical Reaction ◽  
Classification Accuracy ◽  
Similarity Searching ◽  
Reaction Space ◽  
Fine Grained ◽  
Visual Clustering ◽  
Better Than

<div><div><div><p>Organic reactions are usually assigned to classes grouping reactions with similar reagents and mechanisms. Reaction classes facilitate communication of complex concepts and efficient navigation through chemical reaction space. However, the classification process is a tedious task, requiring the identification of the corresponding reaction class template via annotation of the number of molecules in the reactions, the reaction center and the distinction between reactants and reagents. In this work, we show that transformer-based models can infer reaction classes from non-annotated, simple text-based representations of chemical reactions. Our best model reaches a classification accuracy of 98.2%. We also show that the learned representations can be used as reaction fingerprints which capture fine-grained differences between reaction classes better than traditional reaction fingerprints. The unprecedented insights into chemical reaction space enabled by our learned fingerprints is illustrated by an interactive reaction atlas providing visual clustering and similarity searching. </p><p><br></p><p>Code: https://github.com/rxn4chemistry/rxnfp</p><p>Tutorials: https://rxn4chemistry.github.io/rxnfp/</p><p>Interactive reaction atlas: https://rxn4chemistry.github.io/rxnfp//tmaps/tmap_ft_10k.html</p></div></div></div>

scholarly journals Mass transfer with complex reversible chemical reactions—I. Single reversible chemical reaction

1989 ◽  
Vol 44 (10) ◽  
pp. 2295-2310 ◽  
Author(s):  
G.F. Versteeg ◽  
J.A.M. Kuipers ◽  
F.P.H. Van Beckum ◽  
W.P.M. Van Swaaij
Keyword(s):  
Mass Transfer ◽  
Chemical Reactions ◽  
Chemical Reaction ◽  
Reversible Chemical Reaction

Kinetic study of key species and reactions of atmospheric pressure pulsed corona discharge in humid air

2021 ◽  
Author(s):  
Yongkang Peng ◽  
Xiaoyue Chen ◽  
Yeqiang Deng ◽  
Lan Lei ◽  
Zhan Haoyu ◽  
...  
Keyword(s):  
Chemical Reactions ◽  
Chemical Reaction ◽  
Atmospheric Pressure ◽  
Discharge Plasma ◽  
Reaction Rates ◽  
Global Model ◽  
Discharge Process ◽  
Humid Air ◽  
Pressure Discharge ◽  
Atmospheric Pressure Discharge

Abstract The traditional corona discharge fluid model considers only electrons, positive and negative ions, and the discharge parameters are determined using the simplified weighting method involving the partial pressure ratio. Atmospheric pressure discharge plasma in humid air involves three main neutral gas molecule types: N2, O2, and H2O(g). However, in these conditions, the discharge process involves many types of particles and chemical reactions, and the charge and substance transfer processes are complex. At present, the databases of plasma chemical reaction equations are still expanding based on scholarly research. In this study, we examined the key particles and chemical reactions that substantially influence plasma characteristics. In summarizing the chemical reaction model for the discharge process of N2–O2–H2O(g) mixed gases, 65 particle types and 673 chemical reactions were investigated. On this basis, a global model of atmospheric pressure humid air discharge plasma was developed, with a focus on the variation of charged particles densities and chemical reaction rates with time under the excitation of a 0–200 Td pulsed electric field. Particles with a density greater than 1% of the electron density were classified as key particles. For such particles, the top ranking generation or consumption reactions (i.e., where the sum of their rates was greater than 95% of the total rate of the generation or consumption reactions) were classified as key chemical reactions On the basis of the key particles and reactions identified, a simplified global model was derived. A comparison of the global model with the simplified global model in terms of the model parameters, particle densities, reaction rates (with time), and calculation efficiencies demonstrated that both models can adequately identify the key particles and chemical reactions reflecting the chemical process of atmospheric pressure discharge plasma in humid air. Thus, by analyzing the key particles and chemical reaction pathways, the charge and substance transfer mechanism of atmospheric pressure pulse discharge plasma in humid air was revealed, and the mechanism underlying water vapor molecules’ influence on atmospheric pressure air discharge was elucidated.

Chemical Reaction Kinetics in Solution

2004 ◽  
Author(s):  
W. Ronald Fawcett
Keyword(s):  
Reaction Kinetics ◽  
Chemical Reactions ◽  
Chemical Reaction ◽  
Physical Property ◽  
Theoretical Description ◽  
Time Range ◽  
Chemical Changes ◽  
Elementary Reactions ◽  
Chemical Reaction Kinetics ◽  
Liquid Solutions

The kinetics of chemical reactions were first studied in liquid solutions. These experiments involved mixing two liquids and following the change in the concentration of a reactant or product with time. The concentration was monitored by removing a small sample of the solution and stopping the reaction, for example, by rapidly lowering the temperature, or by following a physical property of the system in situ, for example, its color. Although the experiments were initially limited to slow reactions, they established the basic laws governing the rate at which chemical changes occur. The variables considered included the concentrations of the reactants and of the products, the temperature, and the pressure. Thus, the reacting system was examined using the variables normally considered for a system at equilibrium. Most reactions were found to be complex, that is, to be made up of several elementary steps which involved one or two reactants. As the fundamental concepts of chemical kinetics developed, there was a strong interest in studying chemical reactions in the gas phase. At low pressures the reacting molecules in a gaseous solution are far from one another, and the theoretical description of equilibrium thermodynamic properties was well developed. Thus, the kinetic theory of gases and collision processes was applied first to construct a model for chemical reaction kinetics. This was followed by transition state theory and a more detailed understanding of elementary reactions on the basis of quantum mechanics. Eventually, these concepts were applied to reactions in liquid solutions with consideration of the role of the non-reacting medium, that is, the solvent. An important turning point in reaction kinetics was the development of experimental techniques for studying fast reactions in solution. The first of these was based on flow techniques and extended the time range over which chemical changes could be observed from a few seconds down to a few milliseconds. This was followed by the development of a variety of relaxation techniques, including the temperature jump, pressure jump, and electrical field jump methods. In this way, the time for experimental observation was extended below the nanosecond range.

scholarly journals VIII. On the apparent change in weight during chemical reaction

1913 ◽  
Vol 212 (484-496) ◽  
pp. 227-260
Keyword(s):  
Chemical Reactions ◽  
Chemical Reaction ◽  
Experimental Work ◽  
Total Mass ◽  
Apparent Change ◽  
Chemically Reacting

During the year 1890 the late Prof. Landolt inaugurated his prolonged researches upon the apparent alteration in the total mass of chemically reacting substances. From the time of its inception until it was brought to a conclusion in 1907, the experimental work was freely varied both as regards the conditions and the nature of the chemical reactions involved. The methods and precautions adopted, together with the final results obtained, are to be found embodied and set forth in detail in Landolt’s important memoir, “Über die Erhaltung der Masse hei Chemischen Umsetzungen.”* Before proceeding to deal with my own investigations in this field of research, it may not be inappropriate first very briefly to recall the chief features of Landolt’s work and conclusions.

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