Thermodynamic Functions Of Activation Research Articles

Monitoring corrosion and corrosion control of iron in HCl by non-ionic surfactants of the TRITON-X series – Part II. Temperature effect, activation energies and thermodynamics of adsorption

The inhibition characteristics of non-ionic surfactants of the TRITON-X series, namely TRITON-X-100 (TX-100), TRITON-X-165 (TX-165) and TRITON-X-305 (TX-305), on the corrosion of iron was studied in 1.0 M HCl solutions as a function of inhibitor concentration (0.005–0.075 g L −1) and solution temperature (278–338 K). Measurements were conducted based on Tafel extrapolation method. Electrochemical frequency modulation (EFM), a non-destructive corrosion measurement technique that can directly give values of corrosion current without prior knowledge of Tafel constants, is also presented. Experimental corrosion rates determined by the Tafel extrapolation method were compared with corrosion rates obtained by the EFM technique and an independent method of chemical analysis. The chemical method of confirmation of the corrosion rates involved determination of the dissolved cation, using ICP-AES (inductively coupled plasma atomic emission spectrometry). The aim was to confirm validation of corrosion rates measured by the Tafel extrapolation method. Results obtained showed that, in all cases, the inhibition efficiency increased with increase in temperature, suggesting that chemical adsorption occurs. The adsorptive behaviour of the three surfactants followed Temkin-type isotherm. The standard free energies of adsorption decreased with temperature, reflecting better inhibition performance. These findings confirm chemisorption of the tested inhibitors. Thermodynamic activation functions of the dissolution process were also calculated as a function of each inhibitor concentration. All the results obtained from the methods employed are in reasonable agreement.

Kinetics and mechanisms of redox reactions of U, Pu, and Np in tributyl phosphate solutions

Published data on the kinetics of oxidation and reduction of U, Pu, and Np ions with various reagents [HNO3, HNO2, U(IV), etc.] in organic solutions of tributyl phosphate (TBP) are summarized. The rate equations, rate constants, and thermodynamic functions of activation of the reactions are presented. For the majority of reactions, the rate equations in TBP solutions are similar in the form to those for aqueous solutions, which suggests similar reaction mechanisms. A characteristic feature of the reactions in TBP solutions is the dependence of their rate on the H2O concentration, suggesting participation of water molecules in the charge transfer between the reactants.

Degradation Kinetics of Anthocyanin in Blueberry Juice during Thermal Treatment

The kinetics of anthocyanin degradation in blueberry juice during thermal treatment at 40, 50, 60, 70, and 80 degrees C were investigated in the present study. Anthocyanin degradation was analyzed up to the level of 50% retention using a pH differential method. The degradation of anthocyanin at each temperature level followed a first-order kinetic model, and the values of half-life time (t(1/2)) at temperatures of 40, 50, 60, 70, and 80 degrees C were found to be 180.5, 42.3, 25.3, 8.6, and 5.1 h, respectively. The activation energy value of the degradation of the 8.9 degrees Brix blueberry juice during heating was 80.4 kJ.mol(-1). The thermodynamic functions of activation (DeltaG, DeltaH, and DeltaS) have been determined as central to understanding blueberry degradation.

Kinetics of immobilization of 1,2,5-trimethyl-4-dimethylphosphonopiperid-4-ol with maleic anhydride-styrene copolymer

The kinetics of interaction of biologically active piperidol with maleic anhydride-styrene copolymer was studied, and the apparent thermodynamic functions of activation of the process were determined.

Viscosity of Aqueous Solutions of Lithium, Sodium, Potassium, Rubidium and Caesium Cyclohexylsulfamates from 293.15 to 323.15 K

The viscosities of aqueous solutions of lithium, sodium, potassium, rubidium and caesium cyclohexylsulfamates were measured at 293.15, 298.15, 303.15, 313.15 and 323.15 K. The relative viscosity data were analyzed and interpreted in terms of the Kaminsky equation, ηr=1+Ac1/2+Bc+Dc2. The viscosity A-coefficient was calculated from the Falkenhagen-Dole theory. The viscosity B-coefficients are positive and relatively large. Their temperature coefficient ∂B/∂T is negative or near zero for lithium and sodium salts whereas for potassium, rubidium and caesium salts it is positive. The viscosity D-coefficient is positive. This was explained by the size of the ions, structural solute–solute interactions, hydrodynamic effect, and by higher terms of the long-range Debye-Huckel type of forces. From the viscosity B-coefficients the thermodynamic functions of activation of viscous flow were calculated. The limiting partial molar Gibbs energy of activation of viscous flow of the solute was divided into contributions due to solvent molecules and the solute in the transition state. The activation energy of the solvent molecules was calculated using the limiting Gibbs energy of activation for the conductance of the solute ions. The activation energy of the solvent molecules was then discussed in terms of the nature of the alkali-metal ions and their influence on the structure of water. The limiting activation entropy and enthalpy of the solute for activation of viscous flow were interpreted by ion-solvent bond formation or breaking in the transition state of the solvent. The hydration numbers of the investigated electrolytes were calculated from the specific viscosity of the solutions.

Viscosimetric behaviour of n-alkanols with triethylene glycol monomethyl ether at different temperatures

The thermodynamic functions of activation for viscous flow have been evaluated from the dynamic viscosity values of binary mixtures considering Eyring's transition state theory. Kinematic viscosities and densities of binary mixtures containing triethylene glycol monomethyl ether + (2-propanol or 2-butanol or 2-pentanol) over the whole mole fraction range of triethylene glycol monomethyl ether, at four different temperatures and atmospheric pressure were determined. Viscosity deviations and excess Gibbs energies of activation for viscous flow were calculated. All the values of viscosity deviations are negative, at all temperatures. The molar enthalpy of activation for viscous flow and molar entropy of activation for viscous flow functions were obtained. These functions with concentration of the triethylene glycol monomethyl ether show a minimum. These mixtures show a similar behaviour to that of the hydrocarbon–alkanol mixtures. The Grunberg–Nissan and Katti–Chaudrhi parameters were calculated and viscosity data were analyzed on the basis of their treatment.

Intermolecular interactions and properties of mixtures of triethylene glycol with ethanol and isopropyl alcohol

Density and viscosity of solutions formed in the systems triethylene glycol-ethanol and triethylene glycol-isopropyl alcohol were studied in the full concentration range at 20, 40, 50, and 60°C. The thermodynamic activation functions of viscous flow were calculated. The contribution of specific interactions to these functions was determined.

Extraction properties of blends of tetrahydrofurfuryl alcohol with acetone, ethanol, and ethylene glycol

The kinematic viscosity and the density of tetrahydrofurfuryl alcohol blends with acetone, ethanol, and ethylene glycol were examined. The thermodynamic functions of activation of viscous flow were determined. It was found that the dissolving power is determined by the energy density of intermolecular interaction of a solvent in the flow state.

Viscosity and structural features in the phenol-N-methylpyrrolidone and phenol dimethyl sulfoxide systems

The kinematic viscosity, thermodynamic activation functions of the viscous flow, and the mean degree of association of phenol and dilute solutions of aprotic polar solvents (dimethyl sulfoxide, N-methylpyrrolidone) in phenol in the flowing state were evaluated. A procedure was suggested for evaluating the specific interaction term of the specific activation enthalpy of the viscous flow, and the role of the flow in the selective purification of oil fractions was shown.

The role of micellar catalysis from kinetic and thermodynamic investigations of the reaction between bromhexine drug with para-dimethylaminobenzaldehyde

Kinetic study of the condensation reaction of bromhexine with para-dimethylaminobenzaldehyde (DAB) in weakly acidic EthOH/H 2O has been investigated. An opposite first order reaction with respect to bromhexine and zero order with respect to DAB has been observed. The rate constants, activation energies, frequency factors, and other related thermodynamic functions of activation for both forward and reverse reactions have been determined. Standard thermodynamic parameters including equilibrium constant, Δ G°, Δ H°, and Δ S° have been calculated. The effect of the presence of anionic surfactant (sodium dodecyl sulfate, SDS) upon these kinetic and thermodynamic parameters of this reaction in aqueous solution has been examined. The results indicate that the presence of 4 × 10 −3 M SDS increase the forward and reverse rate constants together with equilibrium constant by 104.3, 19.48, and 5.33 times, respectively. A substantial increase in the values of frequency factors of 1 × 10 5 and 2 × 10 4 for forward and reverse reactions, respectively, due to the presence of this amount of SDS has been detected. The observed positive sign of Δ S° in presence and absence of SDS has been confirmed through conductivity measurements. The rate constants in micellar phase, binding constants between each bromhexine and DAB with SDS, and the change in standard chemical potential have been determined at different temperatures. Activation energy, frequency factor, and other related thermodynamic functions of activation in micellar phase have also been calculated. It has been concluded that the increases in the number of collisions between reactants molecules caused by presence of micelles plays a major role in the physicochemical properties of surfactants solutions.

Kinetic and prediction studies of ascorbic acid degradation in normal and concentrate local lemon juice during storage

Kinetics of the loss of ascorbic acid (AA) in local lemon juice of 9° and 50° Brix stored at 25, 35, and 45 °C for 4 months have been investigated. The results indicate that increases of concentrations and temperatures increase the rate of AA degradation. The calculated values of activation energies ( E ≠) and frequency factors ( A) at different Brix imply that the concentration of juice does not change the mechanism of degradation. Thermodynamic functions of activation (Δ G ≠, Δ H ≠, Δ S ≠ and K ≠) have been determined and considered briefly. A direct equation for estimation of the shelf life of stored juice with respect to first-order losses of AA, at any specific temperature and degradation ratio, has been derived and programmed successfully.

Kinetics and thermodynamics of the electrodeposition of palladium, thallium, and tellurium from different baths

Some kinetic and activation thermodynamic functions for the electrodeposition of palladium, thallium, and tellurium from the best selected baths, viz. niclosamide bath [5-chloro-N-(2-chloro-4-nitrophenyl)-2-hydroxybenzamide] for Pd, alizarin red bath for Tl, and salicylaldehyde bath for Te, are determined. Reaction rate constant (k), half-lifetime (t1/2), activation energy (Ea), and such activation thermodynamic parameters as entropy change (ΔS*), enthalpy change (ΔH*), and Gibbs free energy (ΔG*) are calculated by applying the rate theory of the first-order reaction and the Eyring theory of the reaction rate. The effect of temperature change in the range of 30–60°C on the above parameters is studied and thoroughly discussed. The effect of metal type on both the reaction rate and the activation energy is also investigated.

Unusual Solvent Effect on a SN2 Reaction. A Quantum-Mechanical and Kinetic Study of the Menshutkin Reaction between 2-Amino-1-methylbenzimidazole and Iodomethane in the Gas Phase and in Acetonitrile

The quaternization reaction between 2-amino-1-methylbenzimidazole and iodomethane was investigated in the gas phase and in liquid acetonitrile. Both experimental and theoretical techniques were used in this study. In the experimental part of this work, accurate second-order rate constants were obtained for this reaction in acetonitrile from conductivity data in the 293-323 K temperature range and at ambient pressure. From two different empirical equations describing the effect of temperature on reaction rates, thermodynamic functions of activation were calculated. In the theoretical part of this work, the mechanism of this reaction was investigated in the gas phase and in acetonitrile. Two different quantum levels (B3LYP/[6-311++G(3df,3pd)/LanL2DZ]//B3LYP/[6-31G(d)/LanL2DZ] and B3LYP/[6-311++G(3df,3pd)/LanL2DZ]//B3LYP/[6-31+G(d)/LanL2DZ]) were used in the calculations, and the acetonitrile environment was modeled using the polarized continuum model (PCM). In addition, an atoms in molecules (AIM) analysis was made aiming to characterize possible hydrogen bonding. The results obtained by both techniques are in excellent agreement and lead to new insight into the mechanism of the reaction under examination. These include the identification and thermodynamic characterization of the relevant stationary species, the rationalization of the mechanistic role played by the solvent and the amine group adjacent to the nucleophile nitrogen atom, the proposal of alternative paths on the modeled potential energy surfaces, and the origin of the marked non-Arrhenius behavior of the kinetic data in solvent acetonitrile. In particular, the AIM analysis confirmed the operation of intermolecular hydrogen bonds between reactants and between products, both in the gas phase and in solution. It is also concluded that the unusual solvent effect on this Menshutkin reaction stems from the conjunction of a nucleophile possessing a relatively complex chemical structure with a dipolar aprotic solvent that is protophobic.

Viscosities and densities for binary mixtures of N-methylpiperazine with methanol, ethanol, n-propanol, iso-propanol, n-butanol and iso-butanol at 293.15, 298.15 and 303.15 K

Viscosity ( η) and density ( ρ) values are reported for binary mixtures of N-methylpiperazine (NMP) with methanol, ethanol, n-propanol, iso-propanol, n-butanol and iso-butanol over the entire range of mole fraction at 293.15, 298.15, and 303.15 K and atmospheric pressure. The viscosity deviation (Δ η), excess molar volume ( V E), and excess Gibbs energy of activation ( G *E) have been calculated. These results were fitted with Redlich–Kister type polynomial equation. All the investigated systems exhibit very large positive values of Δ η and G *E, and negative values of V E over the whole composition range. The obvious deviations attribute to the strong cross association between the alkanol and NMP molecules through the hydrogen bond of O H ⋯ N. The temperature has significant effect on Δ η and relatively slight effect on V E and G *E. From the experimental data, the thermodynamic functions of activation have been estimated for each binary mixture. The viscosity data have been correlated with several semi-empirical equations. Two-parameter equation of McAllister can give satisfactory results.

Retention of Progesterone by an Activated Carbon: Study of the Adsorption Kinetics

The process by which progesterone in an ethanol solution is retained by Merck granular activated carbon involves a reversible mechanism that conforms to a kinetic equation of unity partial order in both the progesterone concentration in solution, the coverage fraction (θ) of the adsorbing surface and (1−θ). Over the temperature range 10–40°C, the specific adsorption rate varies from 5.8·10−5 to 1.3·10−4 s−1. The thermodynamic activation functions for the process are ΔH*=41.6 kJ/mol and ΔS*=−0.20 kJ/K· mol. The rate of the adsorption-desorption process is primarily determined by diffusion of progesterone molecules in the pores of the sorbent.

Lithium adsorption by acid and sodium amberlite

In this paper we used a previously reported model for examining the adsorption of nonelectrolytes in solution by solid adsorbents to study the adsorption of lithium(I) cations by acid and sodium amberlites, which is an ion-exchange process. Based on the results, both are equilibrium processes and obey a kinetic law with a unity partial order in the Li + concentration. The kinetic results were used to calculate the specific rate constants and thermodynamic activation functions involved. Also, equilibrium isotherms were used to determine the corresponding ion-exchange capacities, the individual equilibrium constants, and the thermodynamic functions for the overall process.

Application of a Single Model to Study the Adsorption Kinetics of Prednisolone on Six Carbonaceous Materials

The knowledge of the adsorption processes of nonelectrolytes from liquid solution on solid materials involves the study of their kinetic and equilibrium aspects as well as the understanding of their thermodynamic functions. However, in most published papers adsorption isotherms are analyzed by using the Giles classification and other proposed equations which are either empirical or based on kinetic or thermodynamic criteria. Our opinion is that both the kinetic and the equilibrium studies must be complementary and that, in general, equations describing the adsorption isotherms come from the kinetic laws governing the different partial processes which determine the global process. These kinetic laws may be derived from single models. In this paper a single model is proposed, which makes it possible to establish a kinetic law satisfactorily fitting a great number of C (concentration) vs t (time) isotherms. This model has been applied to study the adsorption process of prednisolone by six carbonaceous materials from ethanol solution, the specific adsorption rate, and the activation thermodynamic functions being calculated. The results obtained have also been used to analyze the influence of the intraparticle diffusion on the kinetics of the process.

Thermodynamic functions of activation for viscous flow for solutions of polyethylene glycol methyl derivatives with n-alcohols at different temperatures

Viscosity of dilute solutions of mono and dimethyl ether of polyethylene glycol in n-propanol and n-butanol has been determined at different temperatures, between 278.15 and 318.15 K. Thermodynamic functions of activation for viscous flow (Gibbs free energy, enthalpy and entropy) and also partial molar properties were obtained and analyzed using Eyring's theory of rate process applied to viscous flow. From the relation between thermodynamic functions of activation with the mole fraction of the solute, empirical coefficients have been calculated. Contributions to Jones–Dole coefficient, B, were analyzed.

Eyring Functions of Activation for the Viscous Flow of Some Higher Alcohols in Cyclohexane Solutions

The viscosities of solutions of 1-octanol, 1-nonanol, and 1-decanol in cyclohexane up to concentrations of 1.56 molċkg−1 were determined in the temperature range from 293.15 to 333.15 K. Applying Eyring’s transition state theory, the Eyring functions of activation for the viscous flow of binary mixtures, i.e. the molar Gibbs free energy, entropy, and enthalpy were estimated. The correlation coefficients β Y (Y=G, H, or S) were derived and used to discuss the initial effect of the solute on the activation parameters for the viscous flow. From the partial molar thermodynamic functions of activation and the partial molar volumetric data of solute and solvent at infinite dilution, the viscosity coefficient B was determined. For the interpretation of the experimental data, the Unified Interaction Parameter Formalism was used.

Thermodynamic functions of activation of the alkaline hydrolysis of ethyl benzoate and of ethyl p-nitrobenzoate in ethanol–water mixtures of various compositions at different temperatures

This paper presents second-order rate constants for the alkaline hydrolysis of ethyl benzoate and of ethyl p-nitrobenzoate in ethanol–water mixtures in the ethanol mol fraction range 0.16–0.72 and at 278.15–318.15 K measured by a specially developed titrimetric technique. The results show interesting variations in the rate constants with ethanol content at the various temperatures, especially over the mol fraction ranges 0.16–0.25 and 0.4–0.5. The rate constant (k2) data, the Arrhenius activation energy (EA) and pre-exponential factor (A) for ethyl benzoate and the parameters of the fitted polynomials from which other derived thermodynamic functions may be calculated are provided as supplementary material.