Temperature and reaction rate

2017 ◽  
Author(s):  
Andrew Clarke
Keyword(s):  
Reaction Rate ◽  
Muscle Power ◽  
Evolutionary Time ◽  
Gibbs Energy Of Activation ◽  
Physiological Reaction ◽  
Enthalpy Of Activation ◽  
Different Temperatures ◽  
Entropy Of Activation ◽  
Atp Regeneration ◽  
Nervous Conduction

All other things being equal, physiological reaction rate increases roughly exponentially with temperature. Organisms that have adapted over evolutionary time to live at different temperatures can have enzyme variants that exhibit similar kinetics at the temperatures to which they have adapted to operate. Within species whose distribution covers a range of temperatures, there may be differential expression of enzyme variants with different kinetics across the distribution. Enzymes adapted to different optimum temperatures differ in their amino acid sequence and thermal stability. The Gibbs energy of activation tends to be slightly lower in enzyme variants adapted to lower temperatures, but the big change is a decrease in the enthalpy of activation, with a corresponding change in the entropy of activation, both associated with a more open, flexible structure. Despite evolutionary adjustments to individual enzymes involved in intermediary metabolism (ATP regeneration), many whole-organism processes operate faster in tropical ectotherms compared with temperate or polar ectotherms. Examples include locomotion (muscle power output), ATP regeneration (mitochondrial function), nervous conduction and growth.

Solvolysis of Sulphonyl Halides. I. The Hydrolysis of Aromatic Sulphonyl Chlorides in Aqueous Dioxan and Aqueous Acetone

1961 ◽  
Vol 14 (2) ◽  
pp. 190 ◽  
Author(s):  
FE Jenkins ◽  
AN Hambly
Keyword(s):  
Dielectric Constant ◽  
Reaction Rate ◽  
Acid Catalysis ◽  
Salt Effect ◽  
Aqueous Acetone ◽  
Low Dielectric Constant ◽  
Low Dielectric ◽  
Enthalpy Of Activation ◽  
Entropy Of Activation ◽  
Hydrolysis Of

The hydrolysis of benzene, p-toluene, p-bromobenzene, and p-nitrobenzene sulphonyl chlorides in 10-60 wt. % water-dioxan and water-acetone has been shown to follow an SN2 mechanism. The reaction does not show acid catalysis or any " salt " effect. Hammett?s equation does not describe fully the effects of substituents on the reaction rate. For solutions in which water has the same molarity, aqueous acetone gives lower rates than aqueous dioxan when the molarity of water is high but higher rates when the molarity of water is low. Change in the water content of the solvent produces only small changes in the enthalpy of activation except in solutions of low dielectric constant. The reduction in rate as solutions become less aqueous is mainly determined by the entropy of activation becoming more strongly negative.

Enzyme-Catalyzed Decomposition of Dibenzoyl Peroxide in Organic Solvents

2001 ◽  
Vol 56 (7-8) ◽  
pp. 553-558 ◽  
Author(s):  
Elena Horozova ◽  
Nina Dimcheva ◽  
Zinaida Jordanova
Keyword(s):  
Reaction Rate ◽  
Specific Rate ◽  
Michaelis Constant ◽  
Exponential Factor ◽  
Maximum Reaction Rate ◽  
Enthalpy Of Activation ◽  
Maximum Reaction ◽  
Specific Rate Constant ◽  
Entropy Of Activation ◽  
Dibenzoyl Peroxide

Catalytic activity of catalase (CAT, EC 1.11.1.6), immobilized on carbon black NORIT and soot PM-100, with respect to decomposition of dibenzoyl peroxide (BPO) in non-aque-ous media (acetonitrile and tetrachloromethane), was investigated with a quantitative UV-spectrophotometrical approach. Progress of the above reaction was controlled by selected kinetic parameters: the apparent Michaelis constant (Kmapp), the specific rate constant (Ksp), the activation energy (Ea), the maximum reaction rate (Vmax), and the Arrhenius’ pre-exponential factor (Z0). Conclusions on the tentative mechanism of the catalytic process observed were drawn from the calculated values of the Gibbs energy of activation (ΔG*), the enthalpy of activation (ΔH*), and entropy of activation (ΔS*)

scholarly journals Poly(N-isopropylacrylamide-co-methacrylic acid) microgel stabilized copper nanoparticles for catalytic reduction of nitrobenzene

2015 ◽  
Vol 33 (3) ◽  
pp. 627-634 ◽  
Author(s):  
Zahoor H. Farooqi ◽  
Zonarah Butt ◽  
Robina Begum ◽  
Shanza Rhauf Khan ◽  
Ahsan Sharif ◽  
...  
Keyword(s):  
Copper Nanoparticles ◽  
Methacrylic Acid ◽  
Catalytic Reduction ◽  
Aqueous Media ◽  
Activation Parameters ◽  
Reducing Agent ◽  
Different Temperatures ◽  
Entropy Of Activation ◽  
Micro Reactors

Abstract Poly(N-isopropylacrylamide-co-methacrylic acid) microgels [p(NIPAM-co-MAAc)] were synthesized by precipitation polymerization of N-isopropylacrylamide and methacrylic acid in aqueous medium. These microgels were characterized by dynamic light scattering and Fourier transform infrared spectroscopy. These microgels were used as micro-reactors for in situ synthesis of copper nanoparticles using sodium borohydride (NaBH4) as reducing agent. The hybrid microgels were used as catalysts for the reduction of nitrobenzene in aqueous media. The reaction was performed with different concentrations of cat­alyst and reducing agent. A linear relationship was found between apparent rate constant (kapp) and amount of catalyst. When the amount of catalyst was increased from 0.13 to 0.76 mg/mL then kapp was increased from 0.03 to 0.14 min-1. Activation parameters were also determined by performing reaction at two different temperatures. The catalytic process has been discussed in terms of energy of activation, enthalpy of activation and entropy of activation. The synthesized particles were found to be stable even after 14 weeks and showed catalytic activity for the reduction of nitrobenzene.

scholarly journals Kinetic Study of Disulfonimide-Catalyzed Cyanosilylation of Aldehydes by Using a Method of Progress Rates

Synlett ◽  
2020 ◽  
Vol 31 (16) ◽  
pp. 1593-1597 ◽  
Author(s):  
Zhipeng Zhang ◽  
Martin Klussmann ◽  
Benjamin List
Keyword(s):  
Kinetic Study ◽  
Kinetic Data ◽  
Continuous Monitoring ◽  
Reaction Rates ◽  
Catalytic Reactions ◽  
In Situ Ftir ◽  
Bond Forming ◽  
Enthalpy Of Activation ◽  
Entropy Of Activation

Kinetic study of organic reactions, especially multistep catalytic reactions, is crucial to in-depth understanding of reaction mechanisms. Here we report our kinetic study on the chiral disulfonimide-catalyzed cyanosilylation of an aldehyde, which revealed that two molecules of TMSCN are involved in the rate-determining C–C bond-forming step. In addition, the apparent activation energy, enthalpy of activation, and entropy of activation were deduced through a study of the temperature dependence of the reaction rates. More importantly, a novel and efficient method that makes use of the progress rates was developed to treat kinetic data obtained by continuous monitoring of the progress of a reaction by in situ FTIR.

The kinetics of proton and deuteron transfer from 4-nitrophenylnitromethane and l-(4-nitrophenyl)-l-nitroethane to 2,7-dimethoxy-l,8-bis(dimethylamino)naphthalene in acetonitrile solvent

1981 ◽  
Vol 59 (21) ◽  
pp. 3034-3038 ◽  
Author(s):  
Kenneth T. Leffek ◽  
Przemyslaw Pruszynski
Keyword(s):  
Isotope Effect ◽  
Reaction Rate ◽  
Significant Contribution ◽  
Reaction Parameters ◽  
Deuterium Isotope Effect ◽  
First Order ◽  
Enthalpy Of Activation ◽  
Deuteron Transfer ◽  
Slow Dissociation ◽  
Kinetics Of

4-Nitrophenylnitromethane reacts with 2,7-dimethoxy-1,8-bis(dimethylamino)naphthalene in acetonitrile in a bimolecular proton transfer, which shows a primary deuterium isotope effect, kH/kD = 12.2 at 25 °C. The large isotope effect on the enthalpy of activation, (ΔHD≠ – ΔHH≠) = 4.6 ± 0.3 kcal mol−1 is consistent with a significant contribution of proton tunnelling to the reaction rate of the protium substrate.The analogous reaction of 1-(4-nitrophenyl)-1-nitroethane with the same base in acetonitrile gives contrasting kinetics and reaction parameters. The reaction is first order, showing no dependence on base concentration. While the isotope effect kH/kD = 9.3 at 25 °C, the enthalpy of activation difference (ΔHD≠ – ΔHH≠) is only 0.5 ± 0.1 kcal mol−1. It is concluded that the 1-(4-nitrophenyl)-1-nitroethane undergoes a slow dissociation, with a very small dissociation constant, followed by a fast association with the base to yield the carbanion ion-pair.

Analysis on Chemical Reaction Rate of Iron and Molten Tin

2011 ◽  
Vol 393-395 ◽  
pp. 1110-1113
Author(s):  
Hai Bin Li ◽  
Qing Xue Huang ◽  
Jian Mei Wang ◽  
Hai Lian Gui ◽  
Qin Ma
Keyword(s):  
Theoretical Analysis ◽  
Chemical Reaction ◽  
Reaction Rate ◽  
Experimental Results ◽  
Reaction Process ◽  
Different Temperatures ◽  
Chemical Reaction Rate

Based on experimental results and theoretical analysis at different temperatures and time of unit diffusion quantity，the chemical reaction rate in the reaction process between iron and molten tin, is investigated within the range of 260～350°C. The results indicate that the chemical reaction rate at different time decreases rapidly with the time at the same temperature, it take about four minutes to cease. Morever, the numerical value of the reaction rate at different time are close and decrease with the increasing of the temperature.

Kinetic isotope effect and tunnelling in the proton transfer reaction between 2,4,6-trinitrotoluene and 1,1′,3,3′-tetramethylguanidine in dimethylformamide solvent

1979 ◽  
Vol 57 (6) ◽  
pp. 669-672 ◽  
Author(s):  
Arnold Jarczewski ◽  
Przemyslaw Pruszynski ◽  
Kenneth T. Leffek
Keyword(s):  
Proton Transfer ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Transfer Reaction ◽  
Proton Transfer Reaction ◽  
Deuterium Isotope Effect ◽  
Kinetic Isotope ◽  
Enthalpy Of Activation ◽  
Entropy Of Activation ◽  
Large Primary

The proton transfer reaction between 2,4,6-trinitrotoluene and 1,1′,3,3′-tetramethylguanidine in dimethylformamide solvent shows a large primary deuterium isotope effect, kH/kD = 24.3 at 0 °C and 16.9 at 20 °C. The enthalpy of activation difference (ΔHD≠ − ΔHH≠) = 2.6 ± 0.4 kcal mol−1 and the entropy of activation difference (ΔSD≠ − ΔSH≠) = 3.4 ± 1.3 cal mol−1 K−1. This isotope effect, when fitted to Bell's equation, indicates that there is a considerable contribution to this reaction from tunnelling of the proton through the potential energy barrier.

Kinetics of the Substitution of Norbornadiene in Tetracarbonyl(norbomadiene)molybdenum(0) by 2,2'-Bipyridine

2001 ◽  
Vol 56 (3) ◽  
pp. 281-286 ◽  
Author(s):  
Ceyhan Kayran ◽  
Eser Okan
Keyword(s):  
Reaction Rate ◽  
Activation Parameters ◽  
Bipy Ligand ◽  
First Order ◽  
Rate Determining Step ◽  
Vis Spectroscopy ◽  
Different Temperatures ◽  
Ft Ir ◽  
Thermal Substitution ◽  
Kinetics Of

Abstract The kinetics of the thermal substitution of norbornadiene (nbd) by 2,2'-bipyridine (2,2'-bipy) in (CO)4Mo(C7H9) was studied by quantitative FT-IR and UV-VIS spectroscopy. The reaction rate exhibits first-order dependence on the concentration of the starting complex, and the observed rate constant depends on the concentration of both leaving nbd and entering 2,2'-bipy ligand. The mechanism was found to be consistent with the previously proposed one, where the rate determining step is the cleavage of one of the two Mo-olefin bonds. The reaction was performed at four different temperatures (35 -50 °C) and the evaluation of the kinetic data gives the activation parameters which now support states.

scholarly journals Instantaneous activation energy of alkali activated materials

2019 ◽  
Vol 3 ◽  
pp. 121-123
Author(s):  
Shiju Joseph ◽  
Siva Uppalapati ◽  
Ozlem Cizer
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Reaction Rate ◽  
Arrhenius Equation ◽  
Isothermal Calorimetry ◽  
Traditional Methods ◽  
Cement Based Materials ◽  
Different Temperatures ◽  
Higher Temperature ◽  
Alkali Activated

Alkali activated materials (AAM) are generally cured at high temperatures to compensate for the low reaction rate. Higher temperature accelerates the reaction of AAM as in cement-based materials and this effect is generally predicted using Arrhenius equation based on the activation energy. While apparent activation energy is calculated from parallel isothermal calorimetry measurements at different temperatures, instantaneous activation energy is typically measured using a differential scanning calorimeter. Compared to the apparent activation energy, instantaneous activation energy has minimal effects on the microstructural changes due to the variation in temperature. In this work, the evolution of activation energy was determined by traditional methods and was compared with the instantaneous activation energy. It was found that while the activation energy changed with the progress of reaction over traditional methods, the instantaneous activation energy did not show any changes / or remained the same. The instantaneous activation energy was also found to be higher compared to the apparent activation energy determined with traditional methods.

Oxidation of secondary alcohols by sodium N-chlorobenzenesulphonamide in aqueous solution. A kinetic study

1991 ◽  
Vol 56 (8) ◽  
pp. 1671-1679 ◽  
Author(s):  
Chirchingi K. Mythily ◽  
Dandinasivara S. Mahadevappa ◽  
Kanchugarakoppal S. Rangappa
Keyword(s):  
Isotope Effects ◽  
Activation Parameters ◽  
Secondary Alcohols ◽  
Energy Relation ◽  
Linear Free Energy ◽  
Rate Limiting Step ◽  
Different Temperatures ◽  
Entropy Of Activation ◽  
Free Energy Relation ◽  
Solvent Isotope

The kinetics of oxidation of five secondary alcohols by sodium N-chlorobenzenesulphonamide (chloramine-B) has been studied in acid medium at 40°C. The reaction is first order with respect to the oxidant and alcohol and fractional order in [H+]. The influence of added halide ions and of reaction product and the effects of varying ionic strength and dielectric constant of the medium have also been studied. The solvent isotope effects k’(H2O)/k’(D2O) were determined. The rates were studied at four different temperatures and the activation parameters were evaluated. Attempts have been made to arrive at a linear free energy relation through the Taft treatment. An isokinetic relation is observed with β = 248 K, indicating the entropy of activation as the rate controlling factor. Protonated chloramine-T (monochloramine-T) has been postulated as the reactive oxidizing species, the main product of oxidation being the corresponding ketone. A mechanism involving the interaction of protonated haloamine species and the alcohol in a rate limiting step has been proposed.

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