Jerzy Błażejowski

Remarks on the description of reaction kinetics under non-isothermal conditions

Abstract Many fundamental problems regarding the mathematical description of non-isothermal reaction kinetics are still the subject of various considerations. In this communication an attempt is made to clarify some aspects concerned with: (1) the use of the degree of conversion in the rate equations; (2) fundamental relationships describing non-isothermal reaction kinetics; (3) the existence of the total differential of α = f( t , T ); (4) the physical meaning of Doyles assumption; (5) the possibility of the application of non-isothermal techniques on various temperature programs to the investigation of reaction kinetics; and (6) other problems arising on examination of thermodynamics and non-isothermal kinetics of simple thermal processes.

Thermal properties of amine hydrochlorides. Part I. Thermolysis of primary n-alkylammonium chlorides

Abstract Thermogravimetry and differential thermal analysis have been applied to the investigation of the thermal properties of primary n -alkylammonium chlorides of general formula (C n H 2 n +1 NH 3 )Cl, with n = 0–8. Irrespective of the chain-length, the thermolysis of amine hydrochlorides occurs in one step and leads to the total volatilization of the salts. The experimental TG and DTG curves were used for examination of the thermodynamics and kinetics of this process. The values evaluated for the enthalpy of vaporization enable the estimation of some parameters characterizing this group of compounds, namely, the enthalpy of formation and the energy of the crystal lattice of the salts, as well as the enthalpy of formation of the C n H 2 n +1 NH + 3 ions. The Jacobs and Russell-Jones equation, describing the kinetics of sublimation, has been adapted to the dynamic conditions. It was found that this equation approximates very well with the experimental TG data and evaluated values of the apparent activation energy are very close to the values of the enthalpy of volatilization. On the other hand, the standard kinetic treatment of the data indicated that two-dimensional diffusion (D2 mechanism) may govern the volatilization process. The values of characteristic parameters describing the thermal properties of amine hydrochlorides, namely, temperature limits, enthalpy and kinetic constants of thermolysis, depend notably on the length of the aliphatic chain of the amine.

Evaluation of kinetic constants for the solid state reactions under linear temperature increase conditions

Abstract The theory of solid state reaction kinetics considers the dependence of reaction rates on temperature ( T ) and progress of the reaction (α). The term describing the dependence of reaction rates on temperature is usually assumed to be an Arrhenius-type equation: k ( T ) = Z exp(— E/RT ), or the equation predicted by transition state theory: k ( T ) = ZT b exp(— E/RT ). With these assumptions, the equation g(α) = tk ( T ) has been derived, and this form has been satisfactorily applied for the description of solid state reaction kinetics under isothermal conditions. In this work equations similar to those applied in the case of isothermal conditions are proposed for describing the reaction kinetics under linear temperature increase conditions if k ( T ) = Z exp(— E/RT ) if k ( T ) = ZT b exp(— E/RT ) An attempt has been made to apply the above equations, as well as the differential form from the first equation dα/d t = f(α) Z (1 + E/RT ) exp(— E/RT ) to a non-isothermal thermogravimetric experiment. The evaluated kinetic constants are in good agreement with those estimated previously by applying widely used methods of calculation. Therefore, these equations may be considered as simpler and more adequate forms for the description of reaction kinetics under linear temperature increase conditions. Two new statistical functions have been applied in this work which permit the evaluation of E and Z from any kinetic equation. These functions may be used instead of the linear interpolation method, because they allow one to distinguish more easily between possible forms of g(α) or f(α) functions. This approach is recommended especially if one intends to use differential kinetic equations.

The origin of luminescence accompanying electrochemical reduction or chemical decomposition of peroxydisulfates

Abstract The spectral features of the electrochemiluminescence occurring during the reduction of peroxydisulfate anions at magnesium, silver or platinum electrodes (ecl), the luminescence following their decomposition on a magnesium surface (mcl), and the chemiluminescence accompanying the thermal decomposition of peroxydisulfates in acidic media (tcl), were thoroughly examined in order to discover the origin of the light emission. The intensity of emission followed the order ecl>mcl⪢tcl and depended on the method of its generation and other experimental conditions. Probable pathways of the reactions leading to the formation of light-emitting species were examined at the density functional theory level. The theoretical studies and experimental findings seem to indicate that the luminescence originates from 1 O 2 , 1 (O 2 ) 2 and 3 (O 2 ) 2 , the precursors of which are SO 4 •− , HO • , HOO • , HOOH and O 3 formed in the primary and secondary processes following electrochemical reduction or thermal decomposition of peroxydisulfates. Supplementary experiments demonstrated the participation of HOOH in the generation of light emitting entities.

Thermal properties and thermochemistry of alkanaminium bromides

Abstract The thermal behaviour of unbranched compounds of the general formula [(C n H 2 n +1 ) p N-H 4− p ]Br, with n = 0 to 4 and p = 1 to 4, was studied by thermoanalytical methods (DTA, TG and DTG). All the compounds examined undergo decomposition upon heating, leading to their total volatilization. In the case of primary, secondary and tertiary amine hydrobromides, the thermal-dissociation process is accompanied by the release of the appropriate amines and HBr to the gaseous phase. Thermogravimetric curves for these derivatives indicate that the process comprises two stages. In both steps thermal dissociation proceeds via the same chemical mechanism; however, each step is determined by different kinetics. Quaternary salts decompose in only one step which is accompanied by the release of the appropriate tertiary amines and bromoalkanes to the gaseous phase. The latter process requires that the remarkable activation barrier be overcome in addition to that resulting from the thermodynamic requirements. On the other hand, the dissociative volatilization of the former derivatives proceeds essentially without any additional barrier over that imposed by the enthalpy change for the reaction. The enthalpies of the thermal dissociation of hydrobromides were evaluated from the non-isothermal thermogravimetric curves, and these values, together with the thermochemical data available in the literature, were used to evaluate the enthalpies of formation and the crystal-lattice energies of the compounds. The crystal-lattice energy was also examined within the Kapustinskii-Yatsimirskii approach, which assumes an additive character of this quantity. The essential thermal and thermochemical characteristics, as well as the influence of the structure of amines on the thermal behaviour of alkanaminium bromides are also reviewed and discussed.

Thermal reactions of Lead(IV) chloride complexes in the solid state. Part I. Thermolysis of hexachloroplumbates and molecular complexes of PbCl4 with pyridine, quinoline and isoquinoline

Abstract The thermal decomposition of hexachloroplumbic acid salts and of PbCl 4 complexes of pyridine, quinoline and isoquinoline has been investigated by thermogravimetry and differential thermal analysis. The decomposition has also been studied isothermally in a device allowing the analysis of both solid and volatile decomposition products. The products of all thermal reactions comprised PbCl 2 , chlorine, appropriate aromatic bases, their hydrochlorides, chlorinated bases, and other compounds. The influence of sample weight, temperature, rate of removal of volatile products and the effect of certain substances on the course of the thermolysis has also been studied.

Thermal reactions of lead(iv) chloride complexes in the solid state: Part VI. Thermal properties, thermochemistry and kinetics of the thermal decomposition of alkanaminium hexachloroplumbates

Abstract Thermal properties of unbranched compounds of general formula [(CnH2n + 1)pNH4-p]2 PbCl6 with n = 1–4 and p = 2–4, and several other cyclic and open chain branched aliphatic alkanaminium hexachloroplumbates were examined by thermoanalytical methods (DTA, TG, and DTG). Complementary information was gathered by performing thermolyses in an apparatus enabling quantitative determination of evolved chlorine. Thermal decomposition of the compounds studied takes place in two stages: (i) liberation of chlorine (RpNH4-p)2PbCl6(c) → Cl2(g) + [PbCl2 + 2(RpNH4-p)Cl](s) (ii) volatilization of amine hydrochlorides (a = 0) or decomposition of quaternary salts (a = 1) [PbCl2 + 2(RpNH4-pCl](s) → PbCl2(c) + 2Rp-aNH3-p + a(g) + 2(1- a)HCl(g) + 2aRCl(g) Amounts of chlorine evolved were usually less than stoichiometric as some was consumed in secondary processes. For compounds with well-defined decomposition steps the thermodynamics and kinetics of the first stage were examined. The crystal lattice energies of the compounds were estimated using the Kapustinskii-Yatsimirskii equation. Derived values, together with those available from the literature, were used for the estimation of the enthalpy of formation and enthalpy changes for the first step of the thermal decomposition of the salts. The kinetics of the thermal decomposition were analysed by considering two different forms of kinetic equation, i.e. the “classical” form and that based on an assumption: α = f(t,T). No substantial differences between kinetic parameters derived by these methods were found. Some aspects of this problem are discussed, particularly with regard to the existing controversy over the adequate form of kinetic equations under non-isothermal conditions.

Theoretical interpretation of electronic absorption and emission transitions in 9-acridinones

Stationary absorption, fluorescence excitation and fluorescence spectra for 9(10H)-acridinone, 9(10-methyl)-acridinone, 2-methyl-9(10-methyl)-acridinone, 2-nitro-9(10-methyl)-acridinone, 9(10-ethyl)-acridinone and 9(10-phenyl)-acridinone dissolved in 1,4-dioxane, methyl alcohol or acetonitrile, as well as the available spectral characteristics reported by others were compared with those predicted theoretically at the semi-empirical PM3/CI (including the solvent effect within the COSMO model) or PM3/S levels of theory, in order to interpret spectral features of the compounds, i.e. the energies and probabilities of S0-->Sn, S0-->T1, T1-->T2, S1-->S0, T1-->S0 and S1-->T1 transitions. Calculations at the PM3 and PM3/CI levels of theory enabled the structural changes accompanying S0-->S1, S1-->T1 and T1-->S0 transitions to be investigated; they yielded, moreover, basic physicochemical characteristics of the molecules in the ground and excited electronic states. Theoretically predicted dipole moments and charge distributions in the S0, S1 and T1 states provided further insight into the nature of electronic transitions in 9-acridinones. The predicted characteristics correlate quite well with the available experimental ones, thus providing confirmation of the utility of theory in predicting the features of electronically excited molecules and interpreting the electronic transitions occurring in them.

Several expansion formulae of the complementary incomplete gamma function and possible applications

Abstract The complementary incomplete Gamma function, defined by Eulers integral d t , appears in many physicochemical problems. In this paper, several expansion formulae of the above integral are presented. Some properties of these asymptotic series are discussed from the point of view of the possibilities of their application to kinetics problems.

Thermodynamics of the thermal decomposition of calcium oxalate monohydrate examined theoretically

Geometries and energies of isolated CaC2O4·H2O, CaC2O4, CaCO3, CaO, H2O, CO and CO2 were determined at the ab initio level using effective core potential valence basis sets of doublezeta quality, supplemented with polarization functions. The effects of electron correlation were taken into account at the second order Møller-Plesset level of theory. For CaC2O4·H2O, the correlation for the basis set superposition error was also included. Common routines were employed to evaluate entropies, heat capacities, as well as enthalpies and free enthalpies of formation of all entities. The enthalphies and free enthalpies of consecutive dehydration of CaC2O4·H2O, decarbonylation of CaC2O4 and decomposition of CaCO3 towards CaO and CO2 were determined on the basis of avialable data from the literature or those predicted thoretically. Assuming that upon all the above mentioned processes the system maintains equilibrium, the fractions reacted, enthalpy changes and differential dependencies of thesevs. temperature were derived and compared with experimental thermoanalytical data.ZusammenfassungGeometrie und Energien von isoliertem CaC2O4·H2O, CaC2O4, CaCO3, CaO, H2O, CO und CO2 wurden auf dem ab initio Level unter Anwendung von Kernpotential-Valenz-Basissets, ergänzt durch Polarisationsfunktionen bestimmt. Die Effekte der Elektronenkorrelation wurden auf dem Moller-Plesset level zweiten Grades berücksichtigt. Für CaC2O4·H2O wurde auch die Korrelation für den Basissetüberlagerungsfehler inbegriffen. Zur Ableitung der Entropien, Wärmekapazitäten als auch Enthalpien und freien Bildungsenthalpien aller Gebilde wurden die üblichen Routinen verwendet. Die Enthalpien und freien Enthalpien der konsekutiven Dehydratation von CaC2O4·H2O, der Dekarbonylierung von CaC2O4 und der Zersetzung von CaCO3 zu CaO und CO2 wurde auf der Grundlage der zugänglichen Literaturangaben bestimmt. Unter der Annahme, daß das System in allen oben erwähnten, Prozessen im Gleichgewicht bleibt, wurden die Enthalpieänderungen und differentialen Abhängigkeiten derselben von der Temperature abgeleitet und mit den experimentellen thermoanalytischen Angaben verglichen.