Search results for "enthalpy"
showing 10 items of 199 documents
Determination of Kinetic and Thermochemical Parameters of a Substitution Reaction at a Square-Planar Palladium(II) Complex in Water/AOT/n-Heptane Mic…
1995
Abstract The substitution reaction [Pd(bipy)(en)] 2+ + en → [Pd(en) 2 ] 2+ + bipy (where bipy = 2,2′-bipyridine and en = ethylenediamine) has been studied in water and water/AOT/ n -heptane microemulsions at various values of the molar ratio R ( R = [water]/[AOT]) by flow microcalorimetry. From calorimetric data, molar enthalpies of reaction and rate constants were obtained. These quantities indicate that, by increasing R , the reaction becomes less exothermic and its rate constant decreases, trending to the value observed in water. These features can be reasonably rationalized in terms of the peculiar solvation state of reactants inside the AOT reversed micelles and/or the peculiar physico…
A Solar Pond for Feeding a Thermoelectric Generator or an Organic Rankine Cycle System
2017
The world energy demand is continuously growing, which means an increase in consumption for all modern fuels or stronger effort on the development and improvement of renewable technologies. Moreover, Developing Countries claims more energy and they have often wide unutilized or unusable lands. The solar energy represents a useful opportunity for these Countries. The Solar Pond is both a solar collector and a thermal storage for long period and is suitable to use in wide sunny areas. Solar pond technology is able to supply heat for several applications requiring low-grade thermal energy or for electrical power production. In order to produce electrical energy from solar ponds it is necessary…
Thermodynamic Parameters for the Protonation of Poly(allylamine) in concentrated LiCl(aq) and NaCl(aq)
2004
The acid-base properties of poly(allylamine) (MW ) 15 kDa) were determined by potentiometry and calorimetry in aqueous solutions at t ) 25 °C. Potentiometric measurements were carried out in a wide range of ionic strengths (0.1 e I/molâL-1 e 5.0) in NaCl(aq) and LiCl(aq), while enthalpy changes for the protonation of poly(allylamine) were determined by calorimetry in the same ionic strength range but only in NaCl(aq). Analysis of the experimental data was carried out using two different models: the first based on a modified Henderson-Hasselbalch two parameter equation and the second on the three parameter equation proposed by Ho¨gfeldt. Protonation constants are given for both models and io…
Arsenite adsorption on goethite at elevated temperatures
2009
Abstract Experimental closed-system ΔT acid–base titrations between 10 °C and 75 °C were used to constrain a temperature-dependent 1-pK basic Stern model of the goethite surface complexation reactions. Experimental data for the temperature dependence of pHPZC determined by the one-term Van’t Hoff extrapolation yield a value for goethite surface protonation enthalpy of −49.6 kJ mol−1 in good agreement with literature data. Batch titration data between 10 °C and 75 °C with arsenite concentrations between 10 μM and 100 μM yield adsorption curves, which increases with pH, peak at a pH of 9, and decrease at higher pH values. The slope of this bend becomes steeper with increasing temperature. A 1…
Silicate adsorption by goethite at elevated temperatures
2009
Abstract Batch adsorption experiments with relatively low silica concentrations between 10 µM and 100 µM were conducted at three different ionic strength (0.01 − 0.1 M), and four different temperatures between 10 °C and 75 °C, yielding in a total of 550 experimental data points. The residual concentration of monosilicic acid is controlled by an adsorption equilibrium which is dependent on pH. The % Si adsorbed vs. − log[H + ] curves reveal an upward bend with a maximum at about a pH of 9. With acidification below pH 9 the residual Si concentration in the suspensions steadily increases, as well as in the increasingly alkaline pH range. The slope of the latter is becoming steeper with increa…
Heat Pipe-Mediated Control of Fast and Highly Exothermal Reactions
2011
The synthesis of 1-ethyl-3-methylimidazolium ethyl-sulfate ([EMIM]EtSO4) from 1-methyl-imidazole and diethyl sulfate suffers from highly exothermal behavior. Once the activation energy barrier is reached (EA = 89 kJ mol–1), the bimolecular reaction accelerates with a high reaction enthalpy (ΔH = −130 kJ mol–1).(1-3) The excess of heat has to be concurrently dissipated to avoid hot spots or thermal runaways. Depending on the volume flow velocity of the reactants and the applied reactor temperature, the reaction zone can be shifted inside the reactor from the inlet to the outlet and vice versa. Therefore, a sophisticated thermal control, oscillating between providing activation energy and int…
Calorimetric investigation on the formation of palladium nanoparticles in water/AOT/n-heptane microemulsions
1995
The formation enthalpy of palladium nanoparticles in water/sodium bis(2-ethylhexyl) sulfosuccinate (AOT)n-heptane microemulsions as a function of the waterAOT molar ratio (R = [water][AOT]) was measured by a calorimetric technique. The results indicate that at R < 10 the energetic state of the palladium nanoparticles compartmentalized within the reversed AOT micelles is signficantly different from that in bulk water. Effects due to the small size of the palladium nanoparticles and to interactions between nanoparticles and the waterAOT interface are discussed.
Inclusion complexes of triphenylphosphine derivatives and peracetylated-β-cyclodextrin in supercritical carbon dioxide
2008
The supramolecular chemistry of peracetylated-β-CD (perAc-β-CD) as a host for triphenyphosphine derivatives has been studied in supercritical (scCO2) using UV absorption spectroscopy. It was found that the association constant in scCO2 at 40°C and 300 bar is 10 to 1000 times smaller compared to analogous systems in aqueous solvent. Studies of the thermodynamics of the inclusion process found an enthalpy of association of -30 kJ/mole and an entropy of -55 J/moleK. This difference with respect to water is attributed to the absence of the hydrophobic effect in scCO2 due to the much smaller polarity of scCO2 versus water. To further explore the effect of the solvent on the association constant,…
Effect of electrolytical hydrogenation on the thermal stability and crystallization kinetics of METGLASS MBF-50
2007
The effect of electrolytical hydrogenation on both the surface and volume crystallization kinetics and thermal stability of amorphous alloy METGLASS MBF-50 has been investigated. The surface crystallization has been investigated by the exoelectron emission (EEE) technique, whereas the volume crystallization has been followed by differential thermal analysis (DTA). It has been found that both the surface and volume crystallization of investigated material occur in two stages. The surface crystallization occurs at temperature lower and with activation energy distinctly smaller than the volume crystallization. Hydrogenation of the investigated metallic glass enhances its thermal stability by i…
Metal complex-DNA binding: Insights from molecular dynamics and DFT/MM calculations.
2012
Molecular dynamics (MD) simulations, followed by density functional theory/molecular mechanics (DFT/MM) calculations, provided a detailed structure of the binding site between the cationic metallointercalator (dipyrido [3,2-a:2',3'-c]phenazine)(glycinato)copper(II), [Cu(gly)(dppz)](+), and the two dodeca-deoxynucleotide duplexes [dodeca(dG-dC)]2 and [dodeca(dA-dT)]2. Three simultaneous DNA binding types were detected in the fully optimized DFT/MM structures: 1) metal coordination through exocyclic oxygen atoms of nitrogen bases; 2) intercalation of the dppz chromophore between stacked Watson-Crick AT-AT and GC-GC bases; and 3) hydrogen bonding between the glycinato ligand and amine groups o…