• Title/Summary/Keyword: Chemical reaction kinetics

Search Result 739, Processing Time 0.021 seconds

Modeling of diffusion-reaction behavior of sulfate ion in concrete under sulfate environments

  • Zuo, Xiao-Bao;Sun, Wei;Li, Hua;Zhao, Yu-Kui
    • Computers and Concrete
    • /
    • v.10 no.1
    • /
    • pp.79-93
    • /
    • 2012
  • This paper estimates theoretically the diffusion-reaction behaviour of sulfate ion in concrete caused by environmental sulfate attack. Based on Fick's second law and chemical reaction kinetics, a nonlinear and nonsteady diffusion-reaction equation of sulfate ion in concrete, in which the variable diffusion coefficient and the chemical reactions depleting sulfate ion concentration in concrete are considered, is proposed. The finite difference method is utilized to solve the diffusion-reaction equation of sulfate ion in concrete, and then it is used to simulate the diffusion-reaction process and the concentration distribution of sulfate ion in concrete. Afterwards, the experiments for measuring the sulfate ion concentration in concrete are carried out by using EDTA method to verify the proposal model, and results show that the proposed model is basically in agreement with the experimental results. Finally, Numerical example has been completed to investigate the diffusion-reaction behavior of sulfate ion in the concrete plate specimen immersed into sulfate solution.

Interaction Metal Ions with NADH Model Compounds. Cupric Ion Oxidation of Dihydronicotinamides

  • Park, Joon-Woo;Yun, Sung-Hoe;Koh Park, Kwang-Hee
    • Bulletin of the Korean Chemical Society
    • /
    • v.9 no.5
    • /
    • pp.298-303
    • /
    • 1988
  • Kinetic studies on cupric ion ($Cu^{2+}$) oxidation of 1-benzyl- and 1-aryl-1,4-dihydronicotinamides (XNAH) in aqueous solution were performed. In the presence of dioxygen ($O_2$), the reaction followed first order kinetics with respect to both XNAH and $Cu^{2+}$. The oxidation reaction was found to be independent and parallel to the acid-catalyzed hydration reaction of XNAH. The catalytic role of $Cu^{2+}$ for the oxidation of XNAH in the presence of $O_2$ was attributed to $Cu^{2+}/Cu^+$ redox cycle by the reactions with XNAH and $O_2$. The second order rate constants of the Cu2+ oxidation reaction kCu, and acid-catalyzed hydration reaction $k_H$ were strongly dependent on the nature of the substituents in 1-aryl moiety. The slopes of log $k_{Cu}$ vs log $K_H$ and log $k_{Cu}$ vs ${\sigma}_p$ of the substituents plots were 1.64 and -2.2, respectively. This revealed the greater sensitivity of the oxidation reaction rate to the electron density on the ring nitrogen than the hydration reaction rate. A concerted two-electron transfer route involving XNAH-$Cu^{2+}$ complex was proposed for mechanism of the oxidation reaction.

Kinetics and Mechanism of the Pyridinolysis of Diethyl Isothiocyanophosphate in Acetonitrile

  • Adhikary, Keshab Kumar;Lee, Hai-Whang
    • Bulletin of the Korean Chemical Society
    • /
    • v.33 no.3
    • /
    • pp.1042-1046
    • /
    • 2012
  • The kinetics and mechanism of the pyridinolysis ($XC_5H_4N$) of diethyl isothiocyanophosphate are investigated in acetonitrile at $55.0^{\circ}C$. The Hammett and Bronsted plots for substituent X variations in the nucleophiles exhibit the two discrete slopes with a break region between X = 3-Ac and 4-Ac. These are interpreted to indicate a mechanistic change at the break region from a concerted to a stepwise mechanism with rate-limiting expulsion of the isothiocyanate leaving group from a trigonal bipyramidal pentacoordinated intermediate. The relatively large ${\beta}_x$ values with more basic and less basic pyridines imply much greater fraction of frontside nucleophilic attack TSf than that of backside attack TSb.

Thermal Decomposition Characteristics of Ethyl Methacrylate and Styrene Copolymer

  • Kwon, Jae Beom;Lee, Nae Woo;Kim, Nam Seok;Park, Keun Hok;Seul, Soo Duk
    • International Journal of Safety
    • /
    • v.2 no.1
    • /
    • pp.28-33
    • /
    • 2003
  • Thermal decomposition characteristics of ethyl methacrylate (EMA) and Styrene (St.) copolymer was investigated with synthesis at 8$0^{\circ}C$ in a continuous stirred tank reacto (CSTR) using toluene and benzoyl peroxide(BPO) as solvent and initiator, respectively. The thermal decomposition was considered to be side scission at below 30$0^{\circ}C$ and estimated 2nd-order reaction kinetics of EMA/St. copolymer. The activation energies of decomposition on this copolymers were in the ranges of 38-43 kcal/mol for EMA/St. and a good additivity rule was observed in each composition. The thermogravimetric trace curves agreed well with the theoretical calculation.

Kinetic Study on Absorption of Carbonyl Sulfide in Aqueous Monoethanolamine

  • Park, Moon-Ki;Moon, Yung-Soo;Suh, Dong-Soo
    • Environmental Sciences Bulletin of The Korean Environmental Sciences Society
    • /
    • v.4 no.3
    • /
    • pp.195-200
    • /
    • 2000
  • The kinetics of the reaction between carbonyl sulfide and aqueous monoethanolamine were studied over a range of temperature (298-348 K) and amine concentrations using a wetted-sphere absorber. The key physicochemical properties used to interpret the data included the solubility and diffusivity of the COS in the aqueous amine solution. The experimental data were interpreted using a zwitterion mechanism, which produced an Arrhenius plot with third-order kinetic rate constants. The fit of these data was $K_3$=$1.32\times10(sup)10exp(\frac{-6136}{T}}$

  • PDF

Evaluation of Sulfite Solution to Predict Oxygen Transfer Rates in Artificial Lung (인공폐에서의 산소전달 속도를 예측하기 위한 아황산용액의 평가)

  • Lee, S.C.;Kim, K.B.;Jheong, G.R.
    • Proceedings of the KOSOMBE Conference
    • /
    • v.1998 no.11
    • /
    • pp.237-238
    • /
    • 1998
  • The kinetics of sulfite oxidation must be fast and the concentration of sulfite must be low to emulate oxygen uptake by blood. The kinetics were studied yielding a first order rate constant in sulfile, zero order in oxygen. Limitations of the technique were evaluated using the experimental rate constant and an adaptation of Lightfoot's approximation, while the reaction of hemoglobin is reversible and essentially instantaneous, that for sulfite is irreversible and finite. Thus if the approach to saturations not monotonic or if the mass transfer resistance is significantly lowered, e. g. when blood film thicknesses are thinner than a few hundred microns, deviations may occur.

  • PDF

Kinetics of the Rearrangement of $\beta$-4-Nitroazoxybenzene in Strongly Acidic Solution (强酸性 溶液中에서의 $\beta$-4-Nitroazoxybenzene의 轉位反應에 關한 反應速度論的 硏究)

  • Han, Chi-Sun;Lee, Kwi-Ja;Nam Goong, Ha-Il
    • Journal of the Korean Chemical Society
    • /
    • v.11 no.4
    • /
    • pp.173-178
    • /
    • 1967
  • The rearrangement of ${\beta}$-4-nitroazoxybenzene into 4-hydroxy-4'-nitroazobenzene in strongly acidic solutions has been as certained by UV spectrophotometry. The kinetics of the rearrangement in 20 vol. % ethanol and 80 vol. % of aqueous sulfuric acid-water solutions has been studied, and the rearrangement was found to be acid catalyzed pseudo-frst-order reaction. The mechanism of the rearrangement is also discussed.

  • PDF

Kinetics and Mechanism of the Pyridinolysis of Dimethyl Isothiocyanophosphate in Acetonitrile

  • Adhikary, Keshab Kumar;Lee, Hai-Whang
    • Bulletin of the Korean Chemical Society
    • /
    • v.33 no.7
    • /
    • pp.2260-2264
    • /
    • 2012
  • The kinetics and mechanism of the pyridinolysis ($XC_5H_4N$) of dimethyl isothiocyanophosphate are investigated in acetonitrile at $55.0^{\circ}C$. The Hammett and Br$\ddot{o}$nsted plots for substituent X variations in the nucleophiles exhibit two discrete slopes with a break region between X = 3-Ac and 4-Ac. These are interpreted to indicate a mechanistic change at the break region from a concerted to a stepwise mechanism with a rate-limiting expulsion of the isothiocyanate leaving group from the intermediate. The relatively large ${\beta}x$ values imply much greater fraction of frontside nucleophilic attack TSf than that of backside attack TSb. The steric effects of the two ligands play an important role to determine the pyridinolysis rates of isothiocyanophosphates.

Kinetic Studies on Enzymatic Hydrolysis of Cellulose(I) -Effect of Structural Features of Cellulose on Enzyme Adsorption- (섬유소 가수분해반응에 관한 연구(I) -효소흡착에 대한 섬유소의 구조적 특성-)

  • Lee, Yong-Hun;Kim, Chul
    • KSBB Journal
    • /
    • v.6 no.2
    • /
    • pp.157-166
    • /
    • 1991
  • The structural properties of cellulose are significantly changed with the progress of hydrolysis reaction. The effects of changes on such properties of cellulosic substrate as crystallinity, amicessibility of enzyme to the active site of cellulose surface, and particle size on the kinetics of enzymatic hydrolysis have been studied. Among those physical studies, the apparent surface active site of cellulose particle was found to have the most significant effect on the hydrolysis kinetics. Based on the experimental results, the adsorption affinity of enzyme and hydrolysis rate were mainly influenced by the surface roughness of cellulose particle. The extent of accesssible active site may be expressed as the change of particle diameter. The Langmuir isotherm was proposed in terms of enzyme activity to explain the actual action of enzyme protein.

  • PDF

Enzyme Kinetics of Multiple Inhibition in the Presence of Two Reversible Inhibitors

  • Han, Moon H.;Seong, Baik L.
    • Bulletin of the Korean Chemical Society
    • /
    • v.3 no.3
    • /
    • pp.122-129
    • /
    • 1982
  • In order to extend our understanding on the multiple inhibition enzyme kinetics, a general equation of an enzyme reaction in the presence of two different reversible inhibitors was derived by what we call "match-box mechanism" under the combined assumption of steady-state and quasi-equilibrium for inhibitor binding. Graphical methods were proposed to analyze the multiple inhibition of an enzyme by any given sets of different inhibitors, i.e., competitive, noncompetitive, and uncompetitive inhibitors. This method not only gives an interaction factor $({\alpha})$ between two inhibitors, but also discerns ${\alpha}_1$ and ${\alpha}_2$ with and without substrate binding, respectively. The factors involved in the dissociation constants of inhibitors can also be evaluated by the present plot. It is also shown that the present kinetic approach can be extended to other forms of activators or hydrogen ions with some modification.