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Attila K. Horváth - One of the best experts on this subject based on the ideXlab platform.
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Compatible Mechanism for a Simultaneous Description of the Roebuck, Dushman, and Iodate-Arsenous Acid Reactions in an Acidic Medium.
Inorganic chemistry, 2016Co-Authors: László Valkai, Attila K. HorváthAbstract:The iodine–Arsenous Acid (Roebuck), iodide–iodate (Dushman), and iodate–Arsenous Acid reactions have been studied simultaneously by a stopped-flow technique by monitoring the absorbance–time profiles at the isosbestic point of the I2/I3– system (468 nm). Using the well-accepted rate coefficients of iodine hydrolysis, we have proven that iodine is the kinetically active species of the iodine–Arsenous Acid reaction. Strong iodide inhibition of this system is explained by a rapidly established equilibrium between iodine and Arsenous Acid to produce an iodide ion, a hydrogen ion, and a short-lived intermediate H2AsO3I, which is shifted far to the left. Taking into consideration the generally accepted kinetic model of the Dushman reaction where I2O2 plays a key role to account for all of the most important observations in this subsystem and a sequence of simple formal oxygen-transfer reactions between Arsenous Acid and iodic Acid as well as iodous Acid and hypoiodous Acid, we propose a 13-step comprehensive ki...
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A Simple Kinetic Model for Description of the Iodate–Arsenous Acid Reaction: Experimental Evidence of the Direct Reaction
The journal of physical chemistry. A, 2015Co-Authors: György Csekő, László Valkai, Attila K. HorváthAbstract:The autocatalytic iodate-Arsenous Acid reaction was investigated by a stopped-flow instrument under strongly Acidic medium (pH ≤ 1) by monitoring the absorbance-time profiles at 468 nm. The kinetic traces were found to exhibit a perfect sigmoidal shape in stoichiometric excess of iodate with a well-defined and reproducible induction period that depends on the initial concentration of the reactants as well as on the pH. All the experimental curves can be globally fitted by a simple kinetic model involving the direct reaction between the reactants to produce iodide ion, the Dushman and the Roebuck reactions, and two rapid equilibria. Our measurements along with simultaneous evaluation of the kinetic traces clearly support that indeed the initiation reaction exists at strongly Acidic conditions and contributes to the overall kinetics. The measured traces cannot be described adequately by the iodide ion impurity-driven Dushman and Roebuck reactions with assuming no direct reaction at all.
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a simple kinetic model for description of the iodate Arsenous Acid reaction experimental evidence of the direct reaction
Journal of Physical Chemistry A, 2015Co-Authors: György Csekő, László Valkai, Attila K. HorváthAbstract:The autocatalytic iodate-Arsenous Acid reaction was investigated by a stopped-flow instrument under strongly Acidic medium (pH ≤ 1) by monitoring the absorbance-time profiles at 468 nm. The kinetic traces were found to exhibit a perfect sigmoidal shape in stoichiometric excess of iodate with a well-defined and reproducible induction period that depends on the initial concentration of the reactants as well as on the pH. All the experimental curves can be globally fitted by a simple kinetic model involving the direct reaction between the reactants to produce iodide ion, the Dushman and the Roebuck reactions, and two rapid equilibria. Our measurements along with simultaneous evaluation of the kinetic traces clearly support that indeed the initiation reaction exists at strongly Acidic conditions and contributes to the overall kinetics. The measured traces cannot be described adequately by the iodide ion impurity-driven Dushman and Roebuck reactions with assuming no direct reaction at all.
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initial inhomogeneity induced crazy clock behavior in the iodate Arsenous Acid reaction in a buffered medium under stirred batch conditions
Physical Chemistry Chemical Physics, 2015Co-Authors: László Valkai, György Csekő, Attila K. HorváthAbstract:It is unambiguously demonstrated that in the case of an autocatalytic reaction, initial inhomogeneities induced by the imperfectly mixed part of the overall volume may result in a serious irreproducibility of the individual kinetic runs. A statistically meaningful number of repetitions, however, gives rise to a reproducible cumulative probability distribution curve often referred to as a support of the stochastic feature. The iodate–Arsenous Acid reaction being autocatalytic with respect to both iodide and hydrogen ions displays clock behavior. However, the time lag necessary for the appearance of iodine, even in buffered solution, varies in an apparently random manner. Careful analysis of the variation of the different parameters like stirring rate, overall volume, geometry of the reactor and the way of mixing the reactants led us to conclude that the fate of the individual samples is determined at the initial stage when the reacting system is per se inhomogeneous. The place, the size of the so-called ignition volume, where the reacting system is imperfectly stirred, as well as the residence time spent there by the imperfectly mixed reactants all seem to depend on external factors.
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Initial inhomogeneity-induced crazy-clock behavior in the iodate–Arsenous Acid reaction in a buffered medium under stirred batch conditions
Physical chemistry chemical physics : PCCP, 2015Co-Authors: László Valkai, György Csekő, Attila K. HorváthAbstract:It is unambiguously demonstrated that in the case of an autocatalytic reaction, initial inhomogeneities induced by the imperfectly mixed part of the overall volume may result in a serious irreproducibility of the individual kinetic runs. A statistically meaningful number of repetitions, however, gives rise to a reproducible cumulative probability distribution curve often referred to as a support of the stochastic feature. The iodate–Arsenous Acid reaction being autocatalytic with respect to both iodide and hydrogen ions displays clock behavior. However, the time lag necessary for the appearance of iodine, even in buffered solution, varies in an apparently random manner. Careful analysis of the variation of the different parameters like stirring rate, overall volume, geometry of the reactor and the way of mixing the reactants led us to conclude that the fate of the individual samples is determined at the initial stage when the reacting system is per se inhomogeneous. The place, the size of the so-called ignition volume, where the reacting system is imperfectly stirred, as well as the residence time spent there by the imperfectly mixed reactants all seem to depend on external factors.
H. Ševčíková - One of the best experts on this subject based on the ideXlab platform.
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the influence of the starch indicator on front waves in the iodate Arsenous Acid system with applied electric fields
Physical Chemistry Chemical Physics, 2002Co-Authors: Lenka Forštová, H. Ševčíková, J H MerkinAbstract:The effects of the addition of a starch indicator to propagating reaction fronts in the iodate–Arsenous Acid system are considered, both experimentally and by the analysis of a model based on the Dushman–Roebuck kinetic scheme equipped with the complexation reaction between starch, I2 and I3−. Both the experiments and the model show that the starch affects front propagation by slowing the waves down, with an increasing reduction in speed as the starch concentration is increased. This changes the magnitude of the electric field that has to be applied in order to achieve changes in the local stoichiometry. Contrary to the experimental observations, the model shows that the boundaries between the different reaction outcomes are the same, when expressed in terms of the dimensionless parameter ψ = E/v (where E and v are dimensionless versions of the field strength and propagation velocity), as in a previous study by Forstova et al. (J. Phys. Chem., 2000, 104, 9136) where the effects of starch were not included.
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The influence of the starch indicator on front waves in the iodate–Arsenous Acid system with applied electric fields
Physical Chemistry Chemical Physics, 2002Co-Authors: Lenka Forštová, H. Ševčíková, John H. MerkinAbstract:The effects of the addition of a starch indicator to propagating reaction fronts in the iodate–Arsenous Acid system are considered, both experimentally and by the analysis of a model based on the Dushman–Roebuck kinetic scheme equipped with the complexation reaction between starch, I2 and I3−. Both the experiments and the model show that the starch affects front propagation by slowing the waves down, with an increasing reduction in speed as the starch concentration is increased. This changes the magnitude of the electric field that has to be applied in order to achieve changes in the local stoichiometry. Contrary to the experimental observations, the model shows that the boundaries between the different reaction outcomes are the same, when expressed in terms of the dimensionless parameter ψ = E/v (where E and v are dimensionless versions of the field strength and propagation velocity), as in a previous study by Forstova et al. (J. Phys. Chem., 2000, 104, 9136) where the effects of starch were not included.
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Travelling waves in the iodate–Arsenous Acid system
Physical Chemistry Chemical Physics, 1999Co-Authors: John H. Merkin, H. ŠevčíkováAbstract:The equations describing travelling waves in the iodate–Arsenous Acid reaction are discussed, with kinetics based on the Dushman–Roebuck scheme. These equations are used to show how the structure of the wave (its propagation speed and final reaction products) depends on the stoichiometry factor S0, the initial concentration of Arsenous Acid relative to iodate. Different forms are seen in the ranges 0 3. An asymptotic analysis, based on a large parameter arising in the system, is undertaken. This shows that wave structures and propagation speeds are different in these three ranges of S0.
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travelling waves in the iodate Arsenous Acid system
Physical Chemistry Chemical Physics, 1999Co-Authors: John H. Merkin, H. ŠevčíkováAbstract:The equations describing travelling waves in the iodate–Arsenous Acid reaction are discussed, with kinetics based on the Dushman–Roebuck scheme. These equations are used to show how the structure of the wave (its propagation speed and final reaction products) depends on the stoichiometry factor S0, the initial concentration of Arsenous Acid relative to iodate. Different forms are seen in the ranges 0 3. An asymptotic analysis, based on a large parameter arising in the system, is undertaken. This shows that wave structures and propagation speeds are different in these three ranges of S0.
John H. Merkin - One of the best experts on this subject based on the ideXlab platform.
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The influence of the starch indicator on front waves in the iodate–Arsenous Acid system with applied electric fields
Physical Chemistry Chemical Physics, 2002Co-Authors: Lenka Forštová, H. Ševčíková, John H. MerkinAbstract:The effects of the addition of a starch indicator to propagating reaction fronts in the iodate–Arsenous Acid system are considered, both experimentally and by the analysis of a model based on the Dushman–Roebuck kinetic scheme equipped with the complexation reaction between starch, I2 and I3−. Both the experiments and the model show that the starch affects front propagation by slowing the waves down, with an increasing reduction in speed as the starch concentration is increased. This changes the magnitude of the electric field that has to be applied in order to achieve changes in the local stoichiometry. Contrary to the experimental observations, the model shows that the boundaries between the different reaction outcomes are the same, when expressed in terms of the dimensionless parameter ψ = E/v (where E and v are dimensionless versions of the field strength and propagation velocity), as in a previous study by Forstova et al. (J. Phys. Chem., 2000, 104, 9136) where the effects of starch were not included.
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Influence of External Electric Fields on Reaction Fronts in the Iodate-Arsenous Acid System
The Journal of Physical Chemistry A, 2000Co-Authors: Lenka Forštová, Hana Sevcíkova, And Miloš Marek, John H. MerkinAbstract:The propagation of Arsenous Acid−iodate reaction fronts of different net stoichiometries in externally applied dc electric fields is studied for a range of both electric field intensities and initial compositions of the reacting mixture (represented by the stoichiometric factor S0). Regions of three different types of net stoichiometry in the parametric space ℰ/V vs S0, where ℰ is the intensity of the applied electric field and V the reaction front propagation velocity, are determined both experimentally and by analyzing a reaction−diffusion−migration model that includes a realistic kinetic scheme of the reaction studied. Both agreement with and discrepancies between the theoretical predictions and experimental findings are discussed.
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Travelling waves in the iodate–Arsenous Acid system
Physical Chemistry Chemical Physics, 1999Co-Authors: John H. Merkin, H. ŠevčíkováAbstract:The equations describing travelling waves in the iodate–Arsenous Acid reaction are discussed, with kinetics based on the Dushman–Roebuck scheme. These equations are used to show how the structure of the wave (its propagation speed and final reaction products) depends on the stoichiometry factor S0, the initial concentration of Arsenous Acid relative to iodate. Different forms are seen in the ranges 0 3. An asymptotic analysis, based on a large parameter arising in the system, is undertaken. This shows that wave structures and propagation speeds are different in these three ranges of S0.
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travelling waves in the iodate Arsenous Acid system
Physical Chemistry Chemical Physics, 1999Co-Authors: John H. Merkin, H. ŠevčíkováAbstract:The equations describing travelling waves in the iodate–Arsenous Acid reaction are discussed, with kinetics based on the Dushman–Roebuck scheme. These equations are used to show how the structure of the wave (its propagation speed and final reaction products) depends on the stoichiometry factor S0, the initial concentration of Arsenous Acid relative to iodate. Different forms are seen in the ranges 0 3. An asymptotic analysis, based on a large parameter arising in the system, is undertaken. This shows that wave structures and propagation speeds are different in these three ranges of S0.
Marcus J. B. Hauser - One of the best experts on this subject based on the ideXlab platform.
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Acceleration of chemical reaction fronts
The European Physical Journal Special Topics, 2018Co-Authors: Osamu Inomoto, Stefan C. Müller, Ryo Kobayashi, Marcus J. B. HauserAbstract:Chemical fronts and waves travelling in reaction-diffusion systems frequently induce hydrodynamic flow. This adds an additional transport process to the mechanism of spatio-temporal structure formation and can lead to an acceleration of the chemical (reaction) front. We report on the acceleration of travelling chemical fronts elicited by convection, as caused by the Marangoni effect in the monostable iodate-Arsenous Acid reaction in a thin liquid film. At a stoichiometric excess of iodate over Arsenous Acid, the reaction produces a large amount of iodine, which is surface-active. At the reaction front, iodine is transferred from the bulk to the surface inducing spatio-temporal gradients of surface tension that lead to capillary flows. These flows, in turn, promote further iodine adsorption at the surface through hydrodynamic mixing effects. As a consequence, an acceleration of the chemical fronts is observed, even if the concentration difference across the front is constant. After the transient acceleration of the reaction front, it settles at a constant propagation velocity, which is assumed to be regulated by a balance in the mass transfer between the bulk and the surface.
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Buoyancy-driven convection may switch between reactive states in three-dimensional chemical waves.
Physical Review E, 2012Co-Authors: L. Šebestíková, Marcus J. B. HauserAbstract:Traveling waves in an extended reactor, whose width cannot be neglected, represent a three-dimensional (3D) reaction-diffusion-convection system. We investigate the effects of buoyancy-driven convection in such a setting. The 3D waves traveled through horizontal layers of the iodate-Arsenous Acid (IAA) reaction solution containing excess of Arsenous Acid. The depth of the reaction solution was the examined parameter. An increase in the intensity of buoyancy-driven flow caused an increase of the traveling wave velocities. Convection distorted the front of the chemical waves. For layers deeper than h>13 mm, heat release became smaller than heat production causing the emergence of Rayleigh-Benard convection cells. At the interface, a dependency of wave shape on solution depth was observed. For h 13 mm a parabolic shape dominated. For 7
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Buoyancy-driven convection may switch between reactive states in three-dimensional chemical waves.
Physical review. E Statistical nonlinear and soft matter physics, 2012Co-Authors: L. Šebestíková, Marcus J. B. HauserAbstract:Traveling waves in an extended reactor, whose width cannot be neglected, represent a three-dimensional (3D) reaction-diffusion-convection system. We investigate the effects of buoyancy-driven convection in such a setting. The 3D waves traveled through horizontal layers of the iodate-Arsenous Acid (IAA) reaction solution containing excess of Arsenous Acid. The depth of the reaction solution was the examined parameter. An increase in the intensity of buoyancy-driven flow caused an increase of the traveling wave velocities. Convection distorted the front of the chemical waves. For layers deeper than h>13 mm, heat release became smaller than heat production causing the emergence of Rayleigh-Bénard convection cells. At the interface, a dependency of wave shape on solution depth was observed. For h13 mm a parabolic shape dominated. For 7
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buoyancy driven convection may switch between reactive states in three dimensional chemical waves
Physical Review E, 2012Co-Authors: L. Šebestíková, Marcus J. B. HauserAbstract:: Traveling waves in an extended reactor, whose width cannot be neglected, represent a three-dimensional (3D) reaction-diffusion-convection system. We investigate the effects of buoyancy-driven convection in such a setting. The 3D waves traveled through horizontal layers of the iodate-Arsenous Acid (IAA) reaction solution containing excess of Arsenous Acid. The depth of the reaction solution was the examined parameter. An increase in the intensity of buoyancy-driven flow caused an increase of the traveling wave velocities. Convection distorted the front of the chemical waves. For layers deeper than h>13 mm, heat release became smaller than heat production causing the emergence of Rayleigh-Benard convection cells. At the interface, a dependency of wave shape on solution depth was observed. For h 13 mm a parabolic shape dominated. For 7
László Valkai - One of the best experts on this subject based on the ideXlab platform.
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Compatible Mechanism for a Simultaneous Description of the Roebuck, Dushman, and Iodate-Arsenous Acid Reactions in an Acidic Medium.
Inorganic chemistry, 2016Co-Authors: László Valkai, Attila K. HorváthAbstract:The iodine–Arsenous Acid (Roebuck), iodide–iodate (Dushman), and iodate–Arsenous Acid reactions have been studied simultaneously by a stopped-flow technique by monitoring the absorbance–time profiles at the isosbestic point of the I2/I3– system (468 nm). Using the well-accepted rate coefficients of iodine hydrolysis, we have proven that iodine is the kinetically active species of the iodine–Arsenous Acid reaction. Strong iodide inhibition of this system is explained by a rapidly established equilibrium between iodine and Arsenous Acid to produce an iodide ion, a hydrogen ion, and a short-lived intermediate H2AsO3I, which is shifted far to the left. Taking into consideration the generally accepted kinetic model of the Dushman reaction where I2O2 plays a key role to account for all of the most important observations in this subsystem and a sequence of simple formal oxygen-transfer reactions between Arsenous Acid and iodic Acid as well as iodous Acid and hypoiodous Acid, we propose a 13-step comprehensive ki...
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A Simple Kinetic Model for Description of the Iodate–Arsenous Acid Reaction: Experimental Evidence of the Direct Reaction
The journal of physical chemistry. A, 2015Co-Authors: György Csekő, László Valkai, Attila K. HorváthAbstract:The autocatalytic iodate-Arsenous Acid reaction was investigated by a stopped-flow instrument under strongly Acidic medium (pH ≤ 1) by monitoring the absorbance-time profiles at 468 nm. The kinetic traces were found to exhibit a perfect sigmoidal shape in stoichiometric excess of iodate with a well-defined and reproducible induction period that depends on the initial concentration of the reactants as well as on the pH. All the experimental curves can be globally fitted by a simple kinetic model involving the direct reaction between the reactants to produce iodide ion, the Dushman and the Roebuck reactions, and two rapid equilibria. Our measurements along with simultaneous evaluation of the kinetic traces clearly support that indeed the initiation reaction exists at strongly Acidic conditions and contributes to the overall kinetics. The measured traces cannot be described adequately by the iodide ion impurity-driven Dushman and Roebuck reactions with assuming no direct reaction at all.
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a simple kinetic model for description of the iodate Arsenous Acid reaction experimental evidence of the direct reaction
Journal of Physical Chemistry A, 2015Co-Authors: György Csekő, László Valkai, Attila K. HorváthAbstract:The autocatalytic iodate-Arsenous Acid reaction was investigated by a stopped-flow instrument under strongly Acidic medium (pH ≤ 1) by monitoring the absorbance-time profiles at 468 nm. The kinetic traces were found to exhibit a perfect sigmoidal shape in stoichiometric excess of iodate with a well-defined and reproducible induction period that depends on the initial concentration of the reactants as well as on the pH. All the experimental curves can be globally fitted by a simple kinetic model involving the direct reaction between the reactants to produce iodide ion, the Dushman and the Roebuck reactions, and two rapid equilibria. Our measurements along with simultaneous evaluation of the kinetic traces clearly support that indeed the initiation reaction exists at strongly Acidic conditions and contributes to the overall kinetics. The measured traces cannot be described adequately by the iodide ion impurity-driven Dushman and Roebuck reactions with assuming no direct reaction at all.
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initial inhomogeneity induced crazy clock behavior in the iodate Arsenous Acid reaction in a buffered medium under stirred batch conditions
Physical Chemistry Chemical Physics, 2015Co-Authors: László Valkai, György Csekő, Attila K. HorváthAbstract:It is unambiguously demonstrated that in the case of an autocatalytic reaction, initial inhomogeneities induced by the imperfectly mixed part of the overall volume may result in a serious irreproducibility of the individual kinetic runs. A statistically meaningful number of repetitions, however, gives rise to a reproducible cumulative probability distribution curve often referred to as a support of the stochastic feature. The iodate–Arsenous Acid reaction being autocatalytic with respect to both iodide and hydrogen ions displays clock behavior. However, the time lag necessary for the appearance of iodine, even in buffered solution, varies in an apparently random manner. Careful analysis of the variation of the different parameters like stirring rate, overall volume, geometry of the reactor and the way of mixing the reactants led us to conclude that the fate of the individual samples is determined at the initial stage when the reacting system is per se inhomogeneous. The place, the size of the so-called ignition volume, where the reacting system is imperfectly stirred, as well as the residence time spent there by the imperfectly mixed reactants all seem to depend on external factors.
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Initial inhomogeneity-induced crazy-clock behavior in the iodate–Arsenous Acid reaction in a buffered medium under stirred batch conditions
Physical chemistry chemical physics : PCCP, 2015Co-Authors: László Valkai, György Csekő, Attila K. HorváthAbstract:It is unambiguously demonstrated that in the case of an autocatalytic reaction, initial inhomogeneities induced by the imperfectly mixed part of the overall volume may result in a serious irreproducibility of the individual kinetic runs. A statistically meaningful number of repetitions, however, gives rise to a reproducible cumulative probability distribution curve often referred to as a support of the stochastic feature. The iodate–Arsenous Acid reaction being autocatalytic with respect to both iodide and hydrogen ions displays clock behavior. However, the time lag necessary for the appearance of iodine, even in buffered solution, varies in an apparently random manner. Careful analysis of the variation of the different parameters like stirring rate, overall volume, geometry of the reactor and the way of mixing the reactants led us to conclude that the fate of the individual samples is determined at the initial stage when the reacting system is per se inhomogeneous. The place, the size of the so-called ignition volume, where the reacting system is imperfectly stirred, as well as the residence time spent there by the imperfectly mixed reactants all seem to depend on external factors.