Correlation of reaction rates with acidity functions in strongly basic media. Part III. The effect of temperature and leaving group for aromatic S n2 reactions

1967 ◽  
pp. 1076 ◽  
Author(s):  
C. H. Rochester
Keyword(s):  
Reaction Rates ◽  
Effect Of Temperature ◽  
Leaving Group ◽  
Acidity Functions

Bisulfite Degrades Aflatoxin: Effect of Temperature and Concentration of Bisulfite

1978 ◽  
Vol 41 (10) ◽  
pp. 774-780 ◽  
Author(s):  
M. P. DOYLE ◽  
E. H. MARTH
Keyword(s):  
Rate Constant ◽  
Aflatoxin B1 ◽  
Reaction Rate ◽  
Reaction Rates ◽  
Reaction Rate Constant ◽  
Effect Of Temperature ◽  
Kcal Mole ◽  
First Order ◽  
Potassium Acid Phthalate ◽  
Acid Phthalate

Bisulfite reacted with aflatoxin B1 and G1 resulting in their loss of fluorescence. The reaction was first order with rate depending on bisulfite (or the bisulfite and sulfite) concentration(s). Aflatoxin G1 reacted more rapidly with bisulfite than did aflatoxin B1. In the presence of 0.035 M potassium acid phthalate-NaOH buffer (pH 5.5) plus 1.3% (vol/vol) methanol at 25 C, the reaction rate constant for degradation of aflatoxin G1 was 2.23 × 10−2h− and that for aflatoxin B1 was 1.87 × 10−2h− when 50 ml of reaction mixture contained 1.60 g of K2SO3. Besides bisulfite concentrations, temperature influenced reaction rates. The Q10 for the bisulfite-aflatoxin reaction was approximately 2 while activation energies for degrading aflatoxin B1 and aflatoxin G1 were 13.1 and 12.6 kcal/mole, respectively. Data suggest that treating foods with 50 to 500 ppm SO2 probably would not effectively degrade appreciable amounts of aflatoxin. Treating foods with 2000 ppm SO2 or more and increasing the temperature might reduce aflatoxin to an acceptable level.

The Kinetics Effect in SOFCs on Heat and Mass Transfer Limitations: Interparticle, Interphase and Intraparticle Transport

2011 ◽  
Author(s):  
Hedvig Paradis ◽  
Martin Andersson ◽  
Jinliang Yuan ◽  
Bengt Sunde´n
Keyword(s):  
Mass Transfer ◽  
Kinetic Parameters ◽  
Heat And Mass Transfer ◽  
Electrochemical Reaction ◽  
Catalyst Particle ◽  
Reaction Rates ◽  
Transport Processes ◽  
Effect Of Temperature ◽  
Parameter Study ◽  
Time Saving

The transport processes in the porous, micro-structured electrodes are one of the least understood areas of research of the solid oxide fuel cell (SOFC). To enhance the knowledge of the transport process’ impact on the performance in the electrodes, the micro-structure needs to be modeled in detail. But at these smaller scales, it can be both cost and time saving to first conclude at which scales, the limiting action on the transport processes occurs. This study investigates the limiting effect of the kinetic parameters’ on the heat and mass transfer at interparticle, interphase and intraparticle transport level. The internal reaction and the electrochemical reaction rates are studied at three levels in the microscopic range or even smaller. At the intraparticle level the effect of temperature distribution, i.e., heat transfer, within a catalyst particle is often less limiting than the internal mass diffusion process, while at the interphase level the former is more limiting. In this study, no severe risk for transport limitations for the anode and the cathode of the SOFC was found with the chosen kinetic parameters. It was found that the reaction rates constitute the largest risk. A parameter study was conducted by increasing the steam reforming and the electrochemical reaction rates by a factor of 100 without any transport limitations for the same kinetic parameters. The result of this study provides one type of control of the kinetic parameters which in turn have an impact on the reforming reaction rates and the cell performance.

scholarly journals Hot Summers: Effect of Extreme Temperatures on Ozone in Sydney, Australia

Atmosphere ◽  
2018 ◽  
Vol 9 (12) ◽  
pp. 466 ◽  
Author(s):  
Steven Utembe ◽  
Peter Rayner ◽  
Jeremy Silver ◽  
Elise-Andree Guérette ◽  
Jenny Fisher ◽  
...  
Keyword(s):  
Air Quality ◽  
Elevated Temperatures ◽  
Reaction Rates ◽  
Extreme Heat ◽  
Effect Of Temperature ◽  
Biogenic Emissions ◽  
Hot Weather ◽  
Ozone Episodes ◽  
The Impact ◽  
Averaged Model

Poor air quality is often associated with hot weather, but the quantitative attribution of high temperatures on air quality remains unclear. In this study, the effect of elevated temperatures on air quality is investigated in Greater Sydney using January 2013, a period of extreme heat during which temperatures at times exceeded 40 ∘ C, as a case study. Using observations from 17 measurement sites and the Weather Research and Forecasting Chemistry (WRF-Chem) model, we analyse the effect of elevated temperatures on ozone in Sydney by running a number of sensitivity studies in which: (1) the model is run with biogenic emissions generated by MEGAN and separately run with monthly average Model of Emissions of Gases and Aerosols from Nature ( MEGAN) biogenic emissions (for January 2013); (2) the model results from the standard run are compared with those in which average temperatures (for January 2013) are only applied to the chemistry; (3) the model is run using both averaged biogenic emissions and temperatures; and (4 and 5) the model is run with half and zero biogenic emissions. The results show that the impact on simulated ozone through the effect of temperature on reaction rates is similar to the impact via the effect of temperature on biogenic emissions and the relative impacts are largely additive when compared to the run in which both are averaged. When averaged across 17 sites in Greater Sydney, the differences between ozone simulated under standard and averaged model conditions are as high as 16 ppbv. Removing biogenic emissions in the model has the effect of removing all simulated ozone episodes during extreme heat periods, highlighting the important role of biogenic emissions in Australia, where Eucalypts are a key biogenic source.

scholarly journals Kinetics of Alkoxysilanes and Organoalkoxysilanes Polymerization: A Review

Polymers ◽  
2019 ◽  
Vol 11 (3) ◽  
pp. 537 ◽  
Author(s):  
Ahmed Issa ◽  
Adriaan Luyt
Keyword(s):  
Density Functional ◽  
Early Stage ◽  
Reaction Medium ◽  
Reaction Rates ◽  
Dft Methods ◽  
Functional Theory ◽  
Kinetics Of Polymerization ◽  
Leaving Group ◽  
Technical Article ◽  
Kinetics Of

Scientists from various different fields use organo-trialkoxysilanes and tetraalkoxysilanes in a number of applications. The silica-based materials are sometimes synthesized without a good understanding of the underlying reaction kinetics. This literature review attempts to be a comprehensive and more technical article in which the kinetics of alkoxysilanes polymerization are discussed. The kinetics of polymerization are controlled by primary factors, such as catalysts, water/silane ratio, pH, and organo-functional groups, while secondary factors, such as temperature, solvent, ionic strength, leaving group, and silane concentration, also have an influence on the reaction rates. Experiments to find correlations between these factors and reaction rates are restricted to certain conditions and most of them disregard the properties of the solvent. In this review, polymerization kinetics are discussed in the first two sections, with the first section covering early stage reactions when the reaction medium is homogenous, and the second section covering when phase separation occurs and the reaction medium becomes heterogeneous. Nuclear magnetic resonance (NMR) spectroscopy and other techniques are discussed in the third section. The last section summarizes the study of reaction mechanisms by using ab initio and Density Functional Theory (DFT) methods alone, and in combination with molecular dynamics (MD) or Monte Carlo (MC) methods.

scholarly journals Effect of Temperature on Fenton oxidation of young landfill leachate: Kinetic Assessment and Sludge Properties

2013 ◽  
Vol 14 (4) ◽  
pp. 487-495
Keyword(s):  
Landfill Leachate ◽  
Reaction Rates ◽  
Fenton Oxidation ◽  
Volume Index ◽  
Effect Of Temperature ◽  
Molar Ratio ◽  
Initial Reaction ◽  
Capillary Suction ◽  
Sludge Properties ◽  
Increasing Temperature

Treatment of young landfill leachate, collected from municipal solid waste site of city of Konya, was investigated by using the Fenton process. The leachate itself showed the characteristics of pH 7.25, COD 38.2 g L-1 and BOD5 22 g L-1. Ratio of BOD5 to COD with 0.58 indicates that leachate can be defined young. Fenton oxidation of landfill leachate was expressed in two-stage process, where a fast initial reaction (H2O2/Fe2+) was followed by a much slower one (H2O2/Fe3+). Overall kinetics can be described by a second-order rate equation followed by zero-order one. The kinetic studies were undertaken at the different temperatures and reaction rates increcesed by increasing temperature. The apparent kinetic constants at 303 K are k = 3.16 x10-3 L g-1 min-1 and k0 = 0,171 g L-1 min-1, respectively. Fenton reagents effectively degraded the leachate organics and most of the degradation was completed within 30 minutes for all temperatures. The performance of Fenton process was not only presented as a COD removal but also expressed as the amount of generated sludge and its properties. Sludge properties were revealed with Capillary Suction Time (CST) and Sludge Volume Index (SVI). The minimum CST value was obtained at the optimum molar ratio of 4.12 mol/mol and increasing temperature resulted in a positive effect on CST values. All SVI values were significantly low which indicates that sludge itself had good settling properties.

Chemical Kinetics

2021 ◽  
pp. 228-254
Author(s):  
Christopher O. Oriakhi
Keyword(s):  
Activation Energy ◽  
Chemical Kinetics ◽  
Chemical Reactions ◽  
Half Life ◽  
Reaction Rates ◽  
Effect Of Temperature ◽  
Collision Theory ◽  
Rate Laws ◽  
Reaction Orders

Chemical Kinetics discusses the rate at which chemical reactions occur and how these rates can be expressed mathematically, with a review of the factors which affect reaction rates. Topics presented with a numerical focus include reaction rate measurements, rate laws and their components including rate constants, determination of reaction orders from integrated rate laws, and effects of temperature on rates. Reaction half life and its determination are discussed. Collision theory, which forms the basis of the rate law, is presented with emphasis on the effect of temperature on the rate constant and the rate. The Arrhenius equation and the concept of activation energy are discussed with illustrative calculations for determining the energy of activation.

Reaction Mechanisms of Organometallic Systems

2007 ◽  
Author(s):  
Robert B. Jordan
Keyword(s):  
Metal Carbonyl ◽  
Cone Angle ◽  
Reaction Rates ◽  
Organometallic Complexes ◽  
Dielectric Constants ◽  
Substitution Reactions ◽  
Low Dielectric ◽  
Wide Range ◽  
Leaving Group ◽  
The Subject

The general principles discussed in Chapter 3 also apply to reactions of organometallic complexes. Because these systems do not have a wide range of structurally similar complexes with different metal atoms for comparative studies across the Periodic Table, comparisons are usually made down a particular group. However, there is a wide range of ligands available for studies of entering and leaving group effects. This area has been the subject of several recent reviews. A major difference from the systems discussed in Chapter 3 is that many of these complexes are soluble in organic solvents, including hydrocarbons. This can minimize the complicating factor of solvent coordination, but these solvents often have quite low dielectric constants so that various types of preassociation are more probable. The metal carbonyl family of compounds is typical of the range of structures and reactivities of organometallic complexes. The rate of CO exchange was examined in early studies, and this work is the subject of a recent review. The order of reaction rates is as follows: Where the rate law has been determined, the reaction is first-order in [M(CO)R] and zero-order in [CO]. This implies a D mechanism, since a solvent intermediate is unlikely for the "noncoordinating" solvents. This mechanism also is probable for other ligand substitutions. The main mechanistic exception to the above generalizations is V(CO)6, which has an Ia mechanism for PR3 substitution reactions. This compound is unique in that it is the only 17-electron metal carbonyl and also is by far the most labile. Some kinetic results for substitution on V(CO)6 in hexane are given in Table 5.1. The substitution rates have rather low ΔH* values, and the negative ΔS* values are typical of an associative process. The rates for various entering groups correlate with the basicity rather than the size, as measured by the cone angle. It has been suggested that formation of a 19-electron associative intermediate from a 17-electron reactant is much more favorable than a 20-electron intermediate from an 18-electron reactant.

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