6. Changing the identity of matter

2014 ◽  
pp. 86-105
Author(s):  
Peter Atkins
Keyword(s):  
Activation Energy ◽  
Reaction Mechanism ◽  
Equilibrium Constant ◽  
Chemical Kinetics ◽  
Chemical Reactions ◽  
Chemical Dynamics ◽  
Rate Determining Step ◽  
Constant Rate ◽  
Key Terms ◽  
Spontaneous Reaction

A great deal of chemistry is concerned with changing the identity of matter by the deployment of chemical reactions. Physical chemists are interested in a variety of aspects of chemical reactions, including the rates at which they take place (chemical kinetics) and the details of the steps involved during the transformation (chemical dynamics). Chemical reactions can be achieved simply by mixing and heating, but some are stimulated by light (photochemistry) and others by electricity (electrochemistry). ‘Changing the identity of matter’ explains the key terms of chemical kinetics and chemical dynamics such as spontaneous reaction, reaction quotient, equilibrium constant, rate law, reaction mechanism, rate-determining step, activation energy, and catalysis.

scholarly journals Mechanistic Insights into Water-Catalyzed Formation of Levoglucosenone from Anhydrosugar Intermediates by Means of High-Level Theoretical Procedures

2016 ◽  
Vol 69 (9) ◽  
pp. 943 ◽  
Author(s):  
Wenchao Wan ◽  
Li-Juan Yu ◽  
Amir Karton
Keyword(s):  
Activation Energy ◽  
Reaction Mechanism ◽  
Ring Opening ◽  
Reaction Pathway ◽  
Fast Pyrolysis ◽  
Rate Determining Step ◽  
Dehydration Reactions ◽  
High Level ◽  
Multistep Reaction ◽  
Hydration And Dehydration

Levoglucosenone (LGO) is an important anhydrosugar product of fast pyrolysis of cellulose and biomass. We use the high-level G4(MP2) thermochemical protocol to study the reaction mechanism for the formation of LGO from the 1,4:3,6-dianhydro-α-d-glucopyranose (DGP) pyrolysis intermediate. We find that the DGP-to-LGO conversion proceeds via a multistep reaction mechanism, which involves ring-opening, ring-closing, enol-to-keto tautomerization, hydration, and dehydration reactions. The rate-determining step for the uncatalyzed process is the enol-to-keto tautomerization (ΔG‡298 = 68.6 kcal mol–1). We find that a water molecule can catalyze five of the seven steps in the reaction pathway. In the water-catalyzed process, the barrier for the enol-to-keto tautomerization is reduced by as much as 15.1 kcal mol–1, and the hydration step becomes the rate-determining step with an activation energy of ΔG‡298 = 58.1 kcal mol–1.

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.

Insight into the electronic effect of phosphine ligand on Rh catalyzed CO2 hydrogenation by investigating the reaction mechanism

2016 ◽  
Vol 18 (6) ◽  
pp. 4860-4870 ◽  
Author(s):  
Shao-Fei Ni ◽  
Li Dang
Keyword(s):  
Activation Energy ◽  
Reaction Mechanism ◽  
Coordination Sphere ◽  
Metal Hydride ◽  
Electronic Effect ◽  
Catalytic Efficiency ◽  
Co2 Hydrogenation ◽  
Diphosphine Ligand ◽  
Rate Determining Step ◽  
Insight Into

The effect of the outer coordination sphere of the diphosphine ligand on the catalytic efficiency of [Rh(PCH2XRCH2P)2]+ (XR = CH2, N–CH3, CF2) catalyzed CO2 hydrogenation was studied. It was found that the hydricity of the metal hydride bond determined the activation energy of the rate determining step of the reaction.

Pt-Pd Nanoalloy for the Unprecedented Activation of Carbon-Fluorine Bond at Low Temperature

2019 ◽  
Author(s):  
Raghu Nath Dhital ◽  
keigo nomura ◽  
Yoshinori Sato ◽  
Setsiri Haesuwannakij ◽  
Masahiro Ehara ◽  
...  
Keyword(s):  
Activation Energy ◽  
Low Temperature ◽  
Dft Calculations ◽  
Bond Activation ◽  
Mild Conditions ◽  
Selective Transformation ◽  
Rate Determining Step ◽  
Highly Active ◽  
Harsh Conditions ◽  
Reaction Profile

Carbon-Fluorine (C-F) bonds are considered the most inert organic functionality and their selective transformation under mild conditions remains challenging. Herein, we report a highly active Pt-Pd nanoalloy as a robust catalyst for the transformation of C-F bonds into C-H bonds at low temperature, a reaction that often required harsh conditions. The alloying of Pt with Pd is crucial to activate C-F bond. The reaction profile kinetics revealed that the major source of hydrogen in the defluorinated product is the alcoholic proton of 2-propanol, and the rate-determining step is the reduction of the metal upon transfer of the <i>beta</i>-H from 2-propanol. DFT calculations elucidated that the key step is the selective oxidative addition of the O-H bond of 2-propanol to a Pd center prior to C-F bond activation at a Pt site, which crucially reduces the activation energy of the C-F bond. Therefore, both Pt and Pd work independently but synergistically to promote the overall reaction

Full Kinetics and a Mechanism Investigation for the Generation of 4- Substituted 1, 4-Dihydropyridine Derivatives in the Presence of Green Catalyst and Aqueous Medium: Experimental Procedure

2020 ◽  
Vol 17 ◽  
Author(s):  
Sayyed Mostafa Habibi-Khorassani ◽  
Mehdi Shahraki ◽  
Sadegh Talaiefar
Keyword(s):  
Reaction Mechanism ◽  
Reaction Centre ◽  
Green Catalyst ◽  
Experimental Procedure ◽  
Dominant Mechanism ◽  
Rate Determining Step ◽  
12 Steps ◽  
Reaction Constant ◽  
Substituted 1 ◽  
Dihydropyridine Derivatives

Aims and Objective: The main objective of the kinetic investigation of the reaction among ethyl acetoacetate 1, ammoniumacetat 2, dimedone 3 and diverse substitutions of benzaldehyde 4-X, (X= H, NO2, CN, CF3, Cl, CH (CH3)2, CH3, OCH3, OCH3, and OH) for the generation of 4-substituted 1, 4-dihydropyridine derivatives (product 5) was the recognition of the most realistic reaction mechanism. The layout of the reaction mechanism studied kinetically by means of the UV-visible spectrophotometry approach. Materials and Methods: Among the various mechanisms, only mechanism1 (path1) involving 12 steps was recognized as a dominant mechanism (path1). Herein, the reaction between reactants 1 and 2 (kobs= 814.04 M-1 .min-1 ) and also compound 3 and 4-H (kobs= 151.18 M-1 .min-1 ) were the logical possibilities for the first and second fast steps (step1 and step2, respectively). Amongst the remaining steps, only step9 of the dominant mechanism (path1) had substituent groups (X) near the reaction centre that could be directly resonated with it. Results and Discussion: Para electron-withdrawing or donating groups on the compound 4-X increases the rate of the reaction 4 times more or decreases 8.7 times less than the benzaldehyde alone. So, this step is sensitive for monitoring any small or huge changes in the reaction rate. For this reason, step9 is the rate-determining step of the reaction mechanism (path1). Conclusion: The recent result is the agreement with the Hammett description with an excellent dual substituent factor (r = 0.990) and positive value of reaction constant (ρ = +0.9502) which confirmed both the resonance and inductive effects “altogether” contributed on the reaction centre of step9 in the dominant mechanism (path1).

Chemical equilibrium and chemical kinetics

2018 ◽  
Author(s):  
Dennis Sherwood ◽  
Paul Dalby
Keyword(s):  
Free Energy ◽  
Equilibrium Constant ◽  
Gibbs Free Energy ◽  
Chemical Kinetics ◽  
Chemical Equilibrium ◽  
First Principles ◽  
Effect Of Temperature ◽  
Total System ◽  
Free Energies

Building on the previous chapter, this chapter examines gas phase chemical equilibrium, and the equilibrium constant. This chapter takes a rigorous, yet very clear, ‘first principles’ approach, expressing the total Gibbs free energy of a reaction mixture at any time as the sum of the instantaneous Gibbs free energies of each component, as expressed in terms of the extent-of-reaction. The equilibrium reaction mixture is then defined as the point at which the total system Gibbs free energy is a minimum, from which concepts such as the equilibrium constant emerge. The chapter also explores the temperature dependence of equilibrium, this being one example of Le Chatelier’s principle. Finally, the chapter links thermodynamics to chemical kinetics by showing how the equilibrium constant is the ratio of the forward and backward rate constants. We also introduce the Arrhenius equation, closing with a discussion of the overall effect of temperature on chemical equilibrium.

Gas Cell Infrared and Attenuated Total Reflection Infrared Spectroscopic Studies for Organic–Inorganic Interactions in Adsorption of Fulvic Acid on the Goethite Surface Generating Carbon Dioxide

2021 ◽  
pp. 000370282199121
Author(s):  
Yuki Nakaya ◽  
Satoru Nakashima ◽  
Takahiro Otsuka
Keyword(s):  
Carbon Dioxide ◽  
Activation Energy ◽  
Fulvic Acid ◽  
Spectroscopic Studies ◽  
Reaction Model ◽  
Total Reflection ◽  
Attenuated Total Reflection ◽  
Gas Cell ◽  
Rate Determining Step ◽  
Ir Spectroscopic

The generation of carbon dioxide (CO2) from Nordic fulvic acid (FA) solution in the presence of goethite (α-FeOOH) was observed in FA–goethite interaction experiments at 25–80 ℃. CO2 generation processes observed by gas cell infrared (IR) spectroscopy indicated two steps: the zeroth order slower CO2 generation from FA solution commonly occurring in the heating experiments of the FA in the presence and absence of goethite (activation energy: 16–19 kJ mol–1), and the first order faster CO2 generation from FA solution with goethite (activation energy: 14 kJ mol–1). This CO2 generation from FA is possibly related to redox reactions between FA and goethite. In situ attenuated total reflection infrared (ATR-IR) spectroscopic measurements indicated rapid increases with time in IR bands due to COOH and COO– of FA on the goethite surface. These are considered to be due to adsorption of FA on the goethite surface possibly driven by electrostatic attraction between the positively charged goethite surface and negatively charged deprotonated carboxylates (COO–) in FA. Changes in concentration of the FA adsorbed on the goethite surface were well reproduced by the second order reaction model giving an activation energy around 13 kJ mol–1. This process was faster than the CO2 generation and was not its rate-determining step. The CO2 generation from FA solution with goethite is faster than the experimental thermal decoloration of stable structures of Nordic FA in our previous report possibly due to partial degradations of redox-sensitive labile structures in FA.

Vulcanization of Elastomers. 23. The Chemical Kinetics of Vulcanization Reactions and The Physical Properties of The Vulcanizates. I

1960 ◽  
Vol 33 (2) ◽  
pp. 335-341
Author(s):  
Walter Scheele ◽  
Karl-Heinz Hillmer
Keyword(s):  
Activation Energy ◽  
Physical Properties ◽  
Chemical Kinetics ◽  
Kcal Mole ◽  
First Order ◽  
Equilibrium Swelling ◽  
Kinetics Of ◽  
Kinetics Of Vulcanization ◽  
Limiting Value ◽  
Good Agreement

Abstract As a complement to earlier investigations, and in order to examine more closely the connection between the chemical kinetics and the changes with vulcanization time of the physical properties in the case of vulcanization reactions, we used thiuram vulcanizations as an example, and concerned ourselves with the dependence of stress values (moduli) at different degrees of elongation and different vulcanization temperatures. We found: 1. Stress values attain a limiting value, dependent on the degree of elongation, but independent of the vulcanization temperature at constant elongation. 2. The rise in stress values with the vulcanization time is characterized by an initial delay, which, however, is practically nonexistent at higher temperatures. 3. The kinetics of the increase in stress values with vulcanization time are both qualitatively and quantitatively in accord with the dependence of the reciprocal equilibrium swelling on the vulcanization time; both processes, after a retardation, go according to the first order law and at the same rate. 4. From the temperature dependence of the rate constants of reciprocal equilibrium swelling, as well as of the increase in stress, an activation energy of 22 kcal/mole can be calculated, in good agreement with the activation energy of dithiocarbamate formation in thiuram vulcanizations.

Kinetics Studies for Catalytic Oxidation of Methyl Orange over the Heterogeneous Fe/Beta Catalysts

2013 ◽  
Vol 807-809 ◽  
pp. 361-364
Author(s):  
Fang Guo ◽  
Jun Qiang Xu ◽  
Jun Li
Keyword(s):  
Activation Energy ◽  
Hydrogen Peroxide ◽  
Reaction Mechanism ◽  
Methyl Orange ◽  
Incipient Wetness Impregnation ◽  
Kinetics Studies ◽  
Optimum Reaction ◽  
Catalyst Dosage ◽  
Oxidation Degradation ◽  
Degradation Of Methyl Orange

The Fe/Beta catalysts were prepared by conventional incipient wetness impregnation. The catalysis oxidation degradation of methyl orange was carried out in catalyst and H2O2 process. The results indicated that the catalyst and hydrogen peroxide were more benefit to degradation of methyl orange. The reaction condition was optimized. The optimum reaction process was as follow: iron amount of catalyst was 1.25%, the catalyst dosage and H2O2 concentration was 1 mg/L and 1.5 mg/L, and reaction temperature was 70 °C. The apparent activation energy (65 KJ/mol) was obtained according to the arrhenius formula, which was benefit to study the reaction mechanism.

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