Enthalpies Of Dilution Research Articles

Alkanediyl-α,ω-Bis(dimethylalkylammonium Bromide) Surfactants: 9. Effect of the Spacer Carbon Number and Temperature on the Enthalpy of Micellization

The enthalpies of dilution of micellar solutions of several 12-s-12 dimeric surfactants of the alkanediyl-α,ω-bis(dodecyldi-methylammonium bromide) type, differing by the carbon number s of the alkanediyl spacer, and of dodecyltrimethylammonium bromide (DTAB) have been measured calorimetrically, in a range of concentrations extending from well below to well above the critical micelle concentration (cmc). The results permitted the determination of the enthalpy of micellization, ΔH°M, of the investigated surfactants at 25 and 35°C. The values of ΔH°M were always negative and became more negative as the temperature was increased. The plot of −ΔH°M against s showed a shallow minimum at about s=5 and a large decrease of −ΔH°M going from 12-2-12 to 12- 4-12. This effect has been attributed to the contribution to ΔH°M of the hindered rotation of the dodecyl chains around the spacer C–C bond for 12-2-12. This hindrance is shown to rapidly disappear when s is increased from 2 to above 4. The specific heats of micellization, the free energies of micellization, and the entropies of micellization (ΔS°M) have been calculated using the ΔH°M values and the reported cmc and micelle ionization degree data for 12-s-12 surfactants and DTAB. For all surfactants the results show that TΔS°M>−ΔH°M, indicating an entropy-driven micellization.

Enthalpies of dilution of mono-, di- and poly-alcohols in dilute aqueous solutions at 298.15 K

Abstract The enthalpies of dilution of aqueous solutions of methanol, ethanol, l-propanol, 2-propanol, 1-butanol, l-pentanol, 1-hexanol, cyclohexanol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol and poly-alcohol(cyclohexaamylose) have been determined at high dilution as a function of the mole fraction of alcohol at 298.15 K, by a rocking twin-microcalorimeter of the heat-conduction type. A smoothing equation of the enthalpies of dilution against the mole fractions of alcohols are given. The graphical comparison of experimental results with their smoothed values or literature ones, taking into account the dependence of the mole fractions, are also presented. It has been found for the aqueous solutions of shorter n-alcohols than hexanol that at very high dilution, exothermic values of molar enthalpies of dilution from a definite mole fraction of alcohols to infinite dilution with the change of mole fraction is proportional to carbon number of n-alcohols. The molar enthalpies of infinite dilution of aque...

Isopiestic determination of the osmotic and activity coefficients of Rb 2SO4 (aq) and Cs 2SO 4(aq) at T = (298.15 and 323.15) K, and representation with an extended ion-interaction (Pitzer) model

Isopiestic vapor-pressure measurements were made for Rb 2SO 4(aq) from molalitym= (0.16886 to 1.5679 )mol · kg−1atT= 298.15 K and from m= (0.32902 to 1.2282 )mol · kg−1at T= 323.15 K, and for Cs 2SO4 (aq) from m= (0.11213 to 3.10815 )mol · kg−1at T= 298.15 K and fromm= (0.11872 to 3.5095 )mol · kg−1atT= 323.15 K, with NaCl(aq) as the reference standard. Published thermodynamic information for these systems were reviewed and the isopiestic equilibrium molalities and dilution enthalpies were critically assessed and recalculated in a consistent manner. Values of the four parameters of an extended version of Pitzer`s model for osmotic and activity coefficients with an ionic-strength dependent third virial coefficient were evaluated for both systems at both temperatures, as were those of the usual three-parameter Pitzer model. Similarly, parameters of Pitzer`s model for the relative apparent molar enthalpies of dilution were evaluated at T= 298.15 K for both Rb 2SO 4(aq) and Cs 2SO 4(aq) for the more restricted range of m⩽ 0.101 mol · kg−1. Values of the thermodynamic solubility product Ks(Rb2 SO 4, cr, 298.15 K ) = (0.1392 ± 0.0154) and the CODATA compatible standard molar Gibbs free energy of formationΔfGmo (Rb 2SO 4, cr, 298.15 K ) =−(1316.91 ± 0.59)kJ · mol−1, standard molar enthalpy of formationΔfHmo (Rb 2SO 4, cr, 298.15 K ) =−(1435.07 ± 0.60)kJ · mol−1, and standard molar entropy S mo(Rb2 SO 4, cr, 298.15 K ) = (199.60 ± 2.88)J · K−1· mol−1were derived. A sample of one of the lots of Rb 2SO 4(s) used for part of our isopiestic measurements was analyzed by ion chromatography, and was found to be contaminated with potassium and cesium in amounts that significantly exceeded the claims of the supplier. In contrast, analysis by ion chromatography of a lot of Cs 2SO 4(s) used for some of our experiments showed it was highly pure.

The Dilution Enthalpies of Serine in Aqueous Sucrose Solutions at 298.15 K

The Dilution Enthalpies of Serine in Aqueous Sucrose Solutions at 298.15 K

Surface Tensions and Differential Enthalpies of Dilution of the Lithium Bromide + Lithium Iodide + 1,3-Propanediol + Water System

The lithium bromide + lithium iodide + 1,3-propanediol + water (LiBr/LiI mole ratio = 4 and (LiBr + LiI)/HO(CH2)3OH mass ratio = 4) solution was chosen as one of the potential candidates for an air-cooled absorption chiller. For this system, the surface tensions and differential enthalpies of dilution were measured at various temperatures and absorbent (LiBr + LiI + HO(CH2)3OH) concentration ranges by using the capillary rise method and an Isoperibol solution calorimeter, respectively. The measured data were well correlated with the simple polynomial equations. The deviations between the experimental and calculated values in the surface tension and differential enthalpy of dilution measurements were 0.10 and 2.8%.

Flory–Huggins parameter of interaction in polyelectrolyle solutions of chitosan and its alkylated derivative

The enthalpy of dilution of chitosan and alkylchitosan solutions in aqueous 0.3 M acetic acid was experimentally studied over the entire concentration range at 298 K, and the values of Flory–Huggins interaction parameter were determined with the help of a new scaling approach which took into account the electrostatic contribution to the enthalpy of dilution of polyelectrolyte solutions. That made it possible to estimate separately the excluded volume contribution to the enthalpy of dilution and, thus, to calculate the values of χ which appeared to be −0.01 for chitosan and −0.21 for alkylchitosan. It was found out that χ did not depend on the presence of salt in the solution. The hydrophobic modification of chitosan enhanced interaction with water due to the hydrophobic hydration in the aqueous solution.

Thermochemical properties of RE (Gly)4 Im (ClO4) 3 2H2O (RE = La, Pr, Nd, Sm, Eu)

AbstractThe enthalpies of solution in water for five new light rare earth ternary complexes RE(Gly)4Im(ClO4)3 2H2O (RE = La, Pr, Nd, Sm, Eu; Gly‐glycine; Im‐imidazole) were measured by means of a Calvet microcalorimeter. The empirical formula of enthalpy of solution (ΔsolH), relative apparent molar enthalpy (πLi), relative partial molar enthalpy (Li) and enthalpy of dilution (ΔdllH1,2) were drawn up by the data of enthalpies of solution of these complexes. From three plots of the values of standard enthalpy of solution Δsol Hϕ, πLi, Li) versus the values of ionic radius (r) of the light rare earth elements, the grouping effect of lanthanide was observed, showing that the coordination bond between rare earth ion and ligand possesses a certain extent of the property of a covalent bond. The standard enthalpies of solution in water of similar complexes, Ce(Gly)4Im(ClO4)3.2H2O were estimated according to the plot of ΔsolHϕ, versus r.

Aqueous solutions of tris(1,2-diaminoethane)cobalt(III) chloride and tris(1,3-diaminopropane)cobalt(III) chloride atT = 278.15 K. Enthalpy of dilution

The enthalpies of dilution of aqueous solutions of {Co(en)3}Cl3and {Co(tn)3}Cl3(where en= 1,2-diaminoethane andtn= 1,3-diaminopropane) have been measured up to m= 1 mol · kg−1at T= 278.15 K and atmospheric pressure with an isoperibol calorimeter by the long-jump method. Relative apparent molar enthalpies Lφ,mhave been extracted from an empirical polynomial of the molality square root. Previously reported data at T= 298.15 K are compared with the new experimental dilution results. A noticeable decrease in Lφ,mwas observed at every experimental concentration when temperature diminished from 298.15 K to 278.15 K. An inversion in the relative layout for the Lφ,mcurves of aqueous {Co(en)3}Cl3and {Co(tn)3}Cl3was also found.

Influence of the Chemical Surface State of Silica on Adsorption Process of Conventional Cationic and Gemini Surfactants: Thermodynamic Investigations

The aim of this investigation was to study the effect of molecular structure on the adsorption of cationic surfactants onto silica. Thus, the thermodynamics of adsorption of DTAB (dodecyltrimethylammonium bromide) and of the gemini surfactant 12–2–12 (ethanediyl-1,2-bis(dodecyldimethylammonium bromide)) on raw silica (SiNa) and HCl-washed silica (SiH) has been investigated mainly by the microcalorimetric technique. The determination of differential molar enthalpies of adsorption first requires accurate knowledge of the dilution enthalpy of each surfactant under the same experimental conditions as those used during adsorption. The values of the adsorption enthalpies, corrected by the dilution effect, give information on adsorption processes. Moreover, the amount of surfactant adsorbed, the sodium ion concentration, the pH in equilibrated supernatants, and the electrophoretic mobility data complete the calorimetric results. Analysis of the experimental results allows estimation of the number of the surface sites and building up, in both cases, a picture of the adsorption process. The different steps of the adsorption process (by electrostatic and hydrophobic interactions) are described, as are also the different shapes of aggregates at the end of the adsorption. These depend on the state of the surface and the surfactant. A high density of SiNa sites leads to a dense bilayer. A spread density of SiH sites gives rise to pinned micelles.

Enthalpic interactions of glycine in aqueous sodium halide solutions

Dilution enthalpies of glycine in aqueous NaF and NaI solutions of various molalities at 298.15 K have been determined, respectively, by mixing flow microcalorimetry. The results have been analyzed according to the modified McMillan–Mayer model to obtain homogeneous enthalpic interaction coefficients. The effect of the anions on enthalpic pair-wise interaction coefficients has been discussed from the point of view of electrostatic interaction and structural interaction.

Thermodynamic Properties of Aqueous HClO4 to 373 K and at Low Pressure: A Comprehensive Pitzer Ion-Interaction Model

We present a Pitzer ion-interaction model fit to most of the available isopiestic, dilution enthalpy, heat capacity, and volumetric data for HClO4(aq). Osmotic and activity coefficients are accurately reproduced for molalities between infinite dilution and 8 mol kg-1 at 298 K. Isopiestic data at temperatures other than 298 K do not appear to be reliable. The dilution enthalpy data at 298 K are also reproducible to 8 mol kg-1; consequently, HClO4(aq) activities may be calculated to 8 mol kg-1 at 298 K and at somewhat higher or lower temperatures with only minor losses in confidence. Heat capacity data do not extend beyond 1.7 mol kg-1 at 298 K and 1.0 mol kg-1 at T > 328 K, and interlaboratory agreement is poor. Consequently, activity coefficients and thermal properties may only be calculated to about 1 mol kg-1 at 373 K. There are numerous volumetric data for molalities between 0.02 and 18 mol kg-1 and at 298 K; however, there are large variances between datasets at m > 5 mol kg-1. Volumetric data at T > 348 K are limited to one study and m < 1 mol kg-1. The volumetric form of the model is simple but due to disagreement between datasets is considered to have large uncertainties.

Enthalpies of dilution of glycine, l-alanine and l-serine in aqueous ethylene glycol solutions at 298.15 K

Enthalpies of dilution of glycine, l-alanine and l-serine in aqueous ethylene glycol solutions have been measured at 298.15 K by a mixing-flow microcalorimeter. The homogeneous enthalpic interaction coefficients of the three zwitterions have been computed by least-squares fitting on the basis of the McMillan–Mayer theory. The variations of the enthalpic pairwise interaction coefficients with the mass fraction of ethylene glycol in mixtures are interpreted in terms of solute–solute and solute–solvent interactions.

Physicochemical Investigations on the Interaction of Surfactants and Salts with Polyvinylpyrrolidone in Aqueous Medium

Microcalorimetric investigations have been carried out onthe interaction of the surfactants sodium cholate, sodium deoxycholate, tetradecyltrimethylammonium bromide, cetyl(hexadecyl)trimethylammonium bromide, and p-tert-octylphenoxy polyoxy-ethylene ether (Triton X-100) and the salts potassium iodide, sodium benzoate, sodium bromide, and sodium salicylate with the neutral polymer polyvinylpyrrolidone (PVP). The enthalpy of dilution of the surfactants has been measured in the absence and presence of the polymer and the results are compared to determine the effect of PVP on the micellization of the surfactants and the energetics of the process. As well, the micellization activity of the surfactants in the presence of the polymer has been studied by conductometric and fluorimetric methods. The enthalpy of dilution of the salts has been measured to provide an understanding of the nature and magnitude of their interaction with PVP.

Group Contribution Values of the Infinite Dilution Thermodynamic Functions of Hydration for Aliphatic Noncyclic Hydrocarbons, Alcohols, and Ketones at 298.15 K and 0.1 MPa†

A compilation of experimental values of the infinite dilution partial molar Gibbs energy, enthalpy, and heat capacity of hydration, together with molar volumes in water at 298.15 K and 0.1 MPa, is presented for aliphatic noncyclic ketones. These data, combined with the related results for aliphatic noncyclic hydrocarbons and monohydric alcohols, were treated in the framework of a simple first-order group additivity scheme. Numerical values of the contributions to each of the thermodynamic properties are obtained by the least-squares procedure for the following groups: CH3, CH2, CH, C, OH, and CO.

The enthalpy of dilution and thermodynamics of Na2CO3(aq) and NaHCO3(aq) fromT = 298 K toT = 523.15 K and pressure of 40 MPa

Molar enthalpies of dilution ΔdilHmofNa2CO3(aq) were measured from molality m= 1.45 mol · kg−1to m= 0.008 mol · kg−1at seven temperatures from T= 298 K toT= 523 K at the pressure p= 7 MPa, and at four temperatures fromT= 371 K to T= 523 K at the pressurep= 40 MPa. Molar enthalpies of dilutionΔdilHm of NaHCO3(aq) were measured fromm= 0.98 mol · kg−1tom= 0.007 mol · kg−1at the same temperatures and pressures. Hydrolysis and ionization equilibria contribute substantially to the measured enthalpies under many of the conditions of this study. Explicit consideration of these reactions, using thermodynamic quantities from previous studies, facilitates a quantitative representation of apparent molar enthalpies, activity coefficients, and osmotic coefficients with the Pitzer ion-interaction treatment over the ranges of temperature, pressure, and molality of the experiments.

Enthalpies of dilution of cobalt-amine-type salts in aqueous solutions at 25°C

The enthalpies of dilution for aqueous solutions of [Co(en)3]Br3, [Co(pn)3]Cl3, and [Co(tn)3]Cl3 (where en = 1,2-diaminoethane, pn = 1,2-diaminopropane, and tn = 1,3-diaminopropane) have been measured at 25°C, and up to m = 1 mol-kg−1, using an isoperibol calorimeter by the “long-jump” method. Relative apparent molar enthalpies Lφ have been extracted as an empirical equation relating Lφ and m. Previously reported experimental data and theoretical predictions in the restricted primitive model (RPM) for 3:1 and 1:3 aqueous electrolytes are shown together with the new experimental material.

Enthalpies of dilution of aqueous solutions of HCl, MgCl2, CaCl2, and BaCl2 at 300, 325, and 350°C

Dilution enthalpies, measured using isothermal flow calorimetry, are reported for aqueous solutions of BaCl2 at 300°C and 11.0 MPa, MgCl2, CaCl2, and BaCl2 at 325°C and 14.8 MPa, and at 350°C and 17.6 MPa. Previously collected dilution enthalpies for aqueous solutions of MgCl2 and CaCl2 at 300°C and 10.3 MPa and for aqueous solutions of HCl at 250, 275, and 300°C at 10.3 MPa and 320°C at 12.8 MPa were included with the new data at 300°C and 11.0 MPa and at 350°C and 17.6 MPa when fitting the Pitzer parameters. The concentration range of the chloride solutions was 0.5 to 0.02 molal. Parameters for the Pitzer excess Gibbs ion–interaction equation were determined from the fits of the experimental heat data. Equilibrium constants, enthalpy changes, entropy changes, and heat-capacity changes for the association of alkaline earth metal ions and H+ with chloride ion were estimated from the heat data. For all systems, the enthalpy and entropy changes are positive and show accelerating increases with temperature. The resulting equilibrium constants show significant, but smaller, increases with temperature.

Modified UNIFAC (Dortmund). Reliable Model for the Development of Thermal Separation Processes.

Thermal separation processes are of great importance, because they usually cause the greatest part of costs (investment, operating) of a chemical process. For the synthesis, design and optimization of separation processes, in particular, a reliable knowledge of the real phase equilibrium behavior is necessary. If no experimental data are available, group contributions methods can be used to predict the required phase equilibria and excess properties. In recent years, Modified UNIFAC (Dortmund) has become very popular because of its reliable results obtained for different thermodynamic properties such as vapor-liquid equilibria (VLE), solid-liquid equilibria (SLE), azeotropic data, activity coefficients at infinite dilution (γ∞) and excess enthalpies (hE) in a wide temperature range. This paper gives an idea about the large range of applicability and the potential of Modified UNIFAC (Dortmund) for the synthesis, design and optimization of thermal separation processes and other applications of industrial interest. Furthermore, the results of an extensive model comparison for azeotropic data and excess enthalpies are presented.

Preferential configurations in the aqueous solutions of dicarboxylic acids, diols and hydroxyacids: Calorimetric studies at 298 K

Enthalpies of dilution of binary and ternary aqueous solutions of malonic acid derivatives, α,ω-dicarboxylic acids, α,ω-diols and 2-hydroxyacids have been determined by flow microcalorimetry at 298 K. Enthalpic self- and cross-interaction coefficients of the virial expansion of the excess enthalpies were evaluated and interpreted using the “preferential configuration” model. This working model allows the rationalization of the coefficients in terms of nonstatistical interactions in solution. Information is obtained on the influence of the relative position of the functional groups on hydrophobic interactions. When the functional groups are separated, as in α,ω-substances, the hydroxy–carboxy interaction is a better promoter of hydrophobic interactions than hydroxy–hydroxy and carboxy–carboxy interactions. When the two functional groups are on the same carbon atom, as in 2-hydroxyacids, there is an increased cooperativity of hydrophobic interactions compared with malonic acid derivatives (α-dicarboxylic acids). Chiral recognition is not detected in the aqueous solutions of these substances. This failure has been explained in terms of an intramolecular interaction between the hydroxy and carboxy groups which would mask the influence of the chiral carbon atom on the overall interaction.

Enthalpies of Dilution and Excess Molar Enthalpies of an Aqueous Solution of Sulfuric Acid

The enthalpies of dilution of the binary system H2SO4 + H2O have been measured at the temperatures of (283.15, 293.15, 313.15, and 333.15) K using two different calorimeters. The excess molar enthalpies, HE, of the system H2SO4 + H2O are obtained from the enthalpies of dilution data. The enthalpies of dilution and the HE data are reported and compared to literature values.