Apparent Molar Heat Capacities Research Articles

Apparent molar volumes and apparent molar heat capacities of Pr(NO 3) 3(aq), Gd(NO 3) 3(aq), Ho(NO 3) 3(aq), and Y(NO 3) 3(aq) at T = (288.15, 298.15, 313.15, and 328.15) K and p = 0.1 MPa

Relative densities and relative massic heat capacities have been measured for acidified solutions of Y(NO 3) 3(aq), Pr(NO 3) 3(aq), and Gd(NO 3) 3(aq) at T = (288.15, 298.15, 313.15, and 328.15) K and p = 0.1 MPa. In addition, relative densities and massic heat capacities have been measured at the same temperatures and pressure for Y(NO 3) 3(aq) and Ho(NO 3) 3(aq) solutions without excess acid (n.b. measurements at T = 328.15 K for Ho(NO 3) 3(aq) were not performed due to the limited volume of solution available). Apparent molar volumes and apparent molar heat capacities for the aqueous salt solutions have been calculated from the experimental apparent molar properties of the acidified solutions using Young’s rule, whereas the apparent molar properties of the solutions without excess acid were calculated directly from the measured densities and massic heat capacities. The two sets of data for the Y(NO 3) 3(aq) systems provide a check of the internal consistency of the Young’s rule approach we have utilised. The concentration dependences of the apparent molar volumes and heat capacities of the aqueous salt solutions have been modelled at each investigated temperature using the Pitzer ion interaction equations to yield apparent molar properties at infinite dilution. Complex formation within the aqueous rare earth nitrate systems is discussed qualitatively by probing the concentration dependence of apparent molar volumes and heat capacities. In spite of the complex formation in the aqueous rare earth nitrate systems, there is a high degree of self-consistency between the apparent molar volumes and heat capacities at infinite dilution reported in this manuscript and those previously reported for aqueous rare earth perchlorates.

The apparent molal heat capacity, enthalpy, and free energy of seawater fit to the Pitzer equations

The thermochemical properties (osmotic coefficient, enthalpy and heat capacity) of seawater from S=0 to 120 and 0 to 200 °C have been fit to the Pitzer equations. The osmotic coefficient ( ϕ), apparent molal heat capacity ( ϕ Cp) and relative enthalpy ( ϕ L) have been fit to equations of the form ϕ SS − 1 = ( 1 / m ) { − A ϕ I 1.5 / ( 1 + 1.2 I 0.5 ) + m ( B SS ϕ + m C SS ϕ ) } Cp ϕ SS − C ¯ ⁢ p ss 0 = A J { I / ( 1.2 ⁢ m ) } ln ( 1 + 1.2 I 0.5 ) + 2 ⁢ R ⁢ T ⁢ m ( B SS J + m C SS J ) L ϕ SS = ( A H I / 1.2 ⁢ m ) ln ( 1 + 1.2 I 0.5 ) − 2 ⁢ R ⁢ T ⁢ m ( B SS L + m C SS L ) where I is the ionic strength, m is the molality of sea salt ( m=∑ m i , i is an ion); A X ( X= ϕ, J and H) is the Debye–Hückel slope, and C¯p ss 0 is the apparent molal heat capacity of sea salt in water. The Pitzer parameters B SS X and C SS X for sea salt have been fit to functions of temperature in the form Y SS X = ∑ a i ⁢ j ( T − T R ) i where a ij are adjustable parameters, Y SS X is the Pitzer coefficient, T is the temperature in K, and T R=273.15 K). The standard deviations of the seawater fits were 0.0006 J g −1 K −1 for the heat capacity from 0 to 40 °C and 0.0038 J g −1 K −1 from 0 to 200 °C. The extrapolated values of C¯p ss 0 from 0 to 200 °C were in reasonable agreement with the values determined from the major sea salts. The combined c p data have been fit to equations that are consistent with the theoretical values of C¯p ss 0. By appropriate integration of ϕ Cp SS, the apparent molal enthalpy at 298 K and osmotic coefficients at 273 K, equations were determined for all the thermochemical properties as a function of ionic strength and temperature. The thermochemical properties determined in this manner are in good agreement with direct measurements at different salinities and temperatures. The equations can be used to determine all the thermochemical properties of seawater from 0 to 200 °C and I=0 to 2.4 ( S=120).

Review of the Thermodynamic Properties of Mg(NO3)2(aq) and Their Representation with the Standard and Extended Ion‐Interaction (Pitzer) Models at 298.15 K

AbstractFor Abstract see ChemInform Abstract in Full Text.

Partial Molar Heat Capacities and Partial Molar Volumes of All of the Isomeric (C3 to C5) Alkanols at Infinite Dilution in Water at 298.15 K

Apparent molar heat capacities and apparent molar volumes were measured for all isomeric C3 to C5 alkanols in their dilute aqueous solutions at 298.15 K using a differential flow microcalorimeter in conjuntion with a vibrating-tube densimeter. Molar volumes and molar heat capacities of the pure alkanols (except for 2-methyl-2-propanol and 2,2-dimethyl-1-propanol, which are solid at 298.15 K) were determined using the same instrumentation. The concentration dependence of the apparent properties allowed the determination, through extrapolation, of the infinite dilution partial molar volumes and heat capacities of these alkanols in water. These values, combined with the respective pure liquid properties, produced the limiting partial molar excess quantities ( , ). The present measurements agree well with available literature values. The group contribution schemes of Cabani et al. (Cabani, S.; Gianni, P.; Mollica, V.; Lepori, L. Group Contribution to the Thermodynamic Properties of Non-Ionic Organic Solutes i...

Molecular interactions of alkanediols in methanol and in water: density and heat capacity measurements

The heat capacities and densities of dilute solutions of 1,2-alkanediols (1,2-propanediol, 1,2-butanediol, 1,2-pentanediol) and α, ω-alkanediols (1,3-propanediol, 1,4-butanediol, 1,5-pentanediol) in methanol as well as those of 1,2-butanediol and 1,2-pentanediol in water were determined at 298.15 K. Apparent molar heat capacities and volumes for these solutions in methanol and in water were calculated. The scaled particle theory (SPT) was used to determine heat capacity of cavity formation (Δ C p(cav)) and the solute–solvent “interaction term” Δ C p(int). The behaviour of the alkanediols in methanol and in water was compared and discussed.

Thermodynamics of complexation of aqueous 18-crown-6 with potassium ion: apparent molar volumes and apparent molar heat capacities of aqueous 18-crown-6 and of the (18-crown-6 + potassium chloride) complex at temperatures (278.15 to 393.15) K, at molalities (0.02 to 0.3) mol · kg −1, and at the pressure 0.35 MPa

We have measured the densities at temperatures T = (278.15 to 363.15) K and heat capacities at T = (278.15 to 393.15) K of aqueous solutions of 18-crown-6 and of (18-crown-6 + KCl) at molalities m = (0.02 to 0.3) mol · kg −1 and at the pressure 0.35 MPa. We have calculated apparent molar volumes V ϕ and apparent molar heat capacities C p, ϕ for 18-crown-6(aq), and we have applied Young’s Rule and have accounted for chemical speciation and relaxation effects to resolve V ϕ and C p, ϕ for the (18-crown-6: K +,Cl −)(aq) complex in the mixture. We have also calculated estimates of the change in volume Δ r V m, the change in heat capacity Δ r C p,m, the change in enthalpy Δ r H m, and the equilibrium quotient log Q for formation of the complex at T = (278.15 to 393.15) K and m = (0 to 0.3) mol · kg −1.

Apparent Molar Heat Capacities and Apparent Molar Volumes of Aqueous 1,1,1,3,3,3-Hexafluoroisopropanol at Different Temperatures

Specific heats and apparent molar heat capacities of aqueous 1,1,1,3,3,3-hexafluoroiso- proanol (HFIP) have been determined at temperatures from 20.0 to 45.0°C using micro differential scanning calorimetry in the molality range of 0.06741 to 1.24053 mol-kg− 1. Densities and apparent molar volumes have also been determined for aqueous HFIP at temperatures from 10.3 to 30.0°C using digital densimetry in the molality range of 0.04009 to 0.67427 mol-kg− 1. The results of these measurements have been used to calculate the following partial molar quantities and temperature derivatives for aqueous HFIP as a function of temperature: Cp,2,m°, (∂Cp,2,m°/∂T)p, (∂2Cp,2,m°/∂T2)p, V2,m° and (∂V2,m°/∂T)p. The contribution of the — F atom to the partial molar heat capacity and volume has been calculated. The results have been explained in terms of structural changes in water in aqueous HFIP solution. The results obtained in this work contain essential information needed for the development of an equation of state for this system, when used in combination with other thermodynamic properties of aqueous HFIP.

Heat Capacities of Hydroxypropyl-α-, -β-, and -γ-Cyclodextrins in Dilute Aqueous Solution

Apparent molar heat capacities of the hydroxypropyl-α-cyclodextrin, hydroxypropyl-β-cyclodextrin, and hydroxypropyl-γ-cyclodextrin in aqueous solution have been determined at 298.15 K allowing the evaluation of their heat capacities at infinite dilution in water. The calorimetric data do not indicate evidence of aggregation of the hydroxypropylcyclodextrins. The differences in behavior of these modified cyclodextrins compared to linear oligosaccharides, and native cyclodextrins are analyzed.

Review of the Thermodynamic Properties of Mg(NO3)2(aq) and Their Representation with the Standard and Extended Ion-Interaction (Pitzer) Models at 298.15 K

Published thermodynamic data yielding the osmotic coefficients, relative apparent molar enthalpies, and apparent molar heat capacities of Mg(NO3)2(aq) have been collected, recalculated consistently, and critically assessed. The more reliable of these data have been used to evaluate the parameters of the standard three-parameter form of Pitzer's ion-interaction model to higher molalities than previously available, along with the parameters of Archer's four-parameter, extended ion-interaction model at 298.15 K. Published experimental thermodynamic data were essentially represented equally well by these two models, provided that the exponential coefficient α1 of the standard Pitzer model is fixed at the optimum value of α1 = 1.55 kg1/2·mol-1/2 rather than the traditional value of α1 = 2.0 kg1/2·mol-1/2. The use of the standard Pitzer model with this modified α1 value is recommended for Mg(NO3)2(aq). In addition, an empirical equation is given for the variation of the water activity of a saturated solution with temperature, from 273.54 to 328.20 K, with Mg(NO3)2·6H2O(s) as the solid phase.

Modeling Effective Interactions of Micellar Aggregates of Ionic Surfactants with the Gauss-Core Potential

Micellar aggregates of ionic surfactants are known to possess a rich variety of interesting thermodynamic as well as structural properties, which are essentially dominated by simple effective interactions between the aggregates. Because of their technological relevance enormous efforts have been invested to understand and characterize their interactions in solution with the goal of developing substances with novel material’s properties. On a theoretical level several approaches have been proposed to describe their effective interactions adequately, generally based on the DLVO theory. However, these approaches do not take into account aspects of stability of the aggregates and therefore fail in the description of several important characteristics, such as, e.g., the re-entrant behavior of the apparent molal heat capacity appearing with increasing density of the micelles. In this paper we study the effective interactions of these systems by investigating the suitability of the Gauss-core model, to reproduce the relevant thermodynamic properties. To this end, we discuss the Gauss-core model in comparison to the standard DLVO model and demonstrate its aptitude to reproduce the results from calorimetric experiments of the ionic surfactant sodium decanoate in water.

A three-parameter EoS to describe aqueous non-electrolytes at infinite dilution over a wide range of state parameters, with preliminary application to 1:1 electrolytes

A new equation of state (EoS) for describing the thermodynamic properties of aqueous non-electrolytes at infinite dilution is proposed. It is based on the accurate EoS for the solvent (H 2O) given by Hill [21], it requires only three empirical parameters to be fitted to experimental data, and these are independent of temperature and pressure. Knowledge of the thermodynamic properties of the pure gas, together with these three parameters, enables prediction of the whole set of thermodynamic properties of the solute at infinite dilution (chemical potential, entropy, molar volume, and apparent molar heat capacity) over a wide range of temperatures (0–500 °C) and pressures (1–2000 bar), including the near-critical region. In the cases where experimental thermodynamic data are lacking, the empirical parameters can be estimated solely from the known standard-state properties of the solute. The proposed approach has been tested for non-polar (Ar, Ne, H 2, N 2, O 2, CO 2, H 3BO 3), polar (H 2S, NH 3) dissolved molecules, ion pairs (HCl, HF), and aqueous hydrocarbons (CH 4, C 2H 4, C 2H 6, C 3H 8, C 4H 10, C 6H 6). Some preliminary calculations show that the approach also has promise for the description of electrolytes.

Thermodynamic Properties of Dilute NaCl(aq) Solutions near the Critical Point of Water

Completely dissociated aqueous solutions of alkali halides are successfully modeled to about 500−600 K, for instance, by the ion-interaction equations. At higher temperatures, the ions associate to neutral molecules and clusters. In the more concentrated solutions, some “effective chemical continuum” treatment may be applied. Neither approach is, however, suitable for the intermediate region of near-critical temperatures and low solution concentrations, where the ions are only partially associated and thermodynamic properties are subject to rapid changes. A Helmholtz energy model coupled with chemical association was proposed for these systems and used for simultaneous correlation of experimental apparent molar volumes, apparent molar heat capacities, and association constants of dilute NaCl(aq) solutions at temperatures from 573 to 723 K and at concentrations where the solutions are partially associated. Conversion from a MacMillan−Mayer to a Lewis−Randall reference state was included in the calculations. Performance of the model for data description is good, suggesting its application for other associating electrolytes in a wide range of state conditions.

Apparent molar heat capacities and apparent molar volumes of Pr(ClO 4) 3(aq), Gd(ClO 4) 3(aq), Ho(ClO 4) 3(aq), and Tm(ClO 4) 3(aq) at T=(288.15, 298.15, 313.15, and 328.15) K and p=0.1 MPa

Acidified aqueous solutions of Pr(ClO 4) 3(aq), Gd(ClO 4) 3(aq), Ho(ClO 4) 3(aq), and Tm(ClO 4) 3(aq) were prepared from the corresponding oxides by dissolution in dilute perchloric acid. Once characterized with respect to trivalent metal cation and acid content, the relative densities of the solutions were measured at T=(288.15, 298.15, 313.15, and 328.15) K and p=0.1 MPa using a Sodev O2D vibrating tube densimeter. The relative massic heat capacities of the aqueous systems were also determined, under the same temperature and pressure conditions, using a Picker Flow Microcalorimeter. All measurements were made on solutions containing rare earth salt in the concentration range 0.01 ⩽ m/(mol · kg −1) ⩽ 0.2. Relative densities and relative massic heat capacities were used to calculate the apparent molar volumes and apparent molar heat capacities of the acidified salt solutions from which the apparent molar properties of the aqueous salt solutions were extracted by the application of Young's Rule. The concentration dependences of the isothermal apparent molar volumes and heat capacities of each aqueous salt solution were modelled using Pitzer ion-interaction equations. These models produced estimates of apparent molar volumes and apparent molar heat capacities at infinite dilution for each set of isothermal V φ,2 and C p φ,2 values. In addition, the temperature and concentration dependences of the apparent molar volumes and apparent molar heat capacities of the aqueous rare earth perchlorate salt solutions were modelled using modified Pitzer ion-interaction equations. The latter equations utilized the Helgeson, Kirkham, and Flowers equations of state to model the temperature dependences (at p=0.1 MPa) of apparent molar volumes and apparent molar heat capacities at infinite dilution. The results of the latter models were compared to those previously published in the literature. Apparent molar volumes and apparent heat capacities at infinite dilution for the trivalent metal cations Pr 3+(aq), Gd 3+(aq), Ho 3+(aq), and Tm 3+(aq) were calculated using the conventions V 2 ∘(H +(aq)) ≡ 0 and C p2 ∘(H +(aq)) ≡ 0 and have been compared to other values reported in the literature.

Apparent molar volumes and apparent molar heat capacities of aqueous d-lactose · H 2O at temperatures from (278.15 to 393.15) K and at the pressure 0.35 MPa

Apparent molar volumes V φ and apparent molar heat capacities C p, φ were determined for aqueous solutions of d-lactose · H 2O at molalities (0.01 to 0.34) mol · kg −1 at temperatures (278.15 to 393.15) K, and at the pressure 0.35 MPa. Our V φ values were calculated from densities obtained using a vibrating tube densimeter, and our C p, φ values were obtained using a twin fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter. Our results for d-lactose(aq) and for d-lactcose · H 2O were fitted to functions of m and T and compared with the literature results for aqueous d-glucose and d-galactose solutions. Infinite dilution partial molar volumes V 2 ∘ and heat capacities C p,2 ∘ are given over the range of temperatures.

Interaction of 2,2,2-trifluoroethanol with proteins: calorimetric, densimetric and surface tension approach

The thermal denaturation of hen egg-white lysozyme was studied in the presence of 2,2,2-trifluoroethanol (TFE) at various pH values using micro differential scanning calorimetry. Quantitative thermodynamic parameters accompanying the thermal transitions were evaluated. It is observed that thermal unfolding of lysozyme in the presence of TFE upto a concentration of 4.0 mol dm −3 follows a two-state denaturation mechanism as indicated by the equality of van't Hoff and calorimetric enthalpies. The finer details of interaction were studied by measuring the partial molar volume of some constituent amino acids and glycine peptides from water to aqueous TFE at 298.15 K. The physico-chemical properties of aqueous TFE: apparent molar heat capacities, apparent molar volumes and surface tension were measured to understand the intrinsic properties of the cosolvent as well. From the correlation among the thermal unfolding data on lysozyme in aqueous TFE, calculated preferential interaction parameters, physico chemical properties of aqueous TFE and partial molar volumes of transfer, it is concluded that both solvent mediated effect and direct interaction constitute the mechanism of TFE–protein interactions.

Apparent molar volumes and apparent molar heat capacities of aqueous nickel(II) nitrate, copper(II) nitrate, and zinc(II) nitrate at temperatures from (278.15 to 393.15) K at the pressure 0.35 MPa

Apparent molar volumes V φ and apparent molar heat capacities C p, φ were determined for aqueous solutions of nickel(II) nitrate, copper(II) nitrate, and zinc(II) nitrate at molalities m=(0.01 to 0.5) mol · kg −1, and at the pressure p=0.35 MPa. Solution densities obtained using a vibrating-tube densimeter at T=(278.15 to 368.15) K were used to calculate V φ values. Heat capacity measurements obtained with a twin fixed-cell, differential-output, power-compensating, temperature-scanning calorimeter at T=(278.15 to 393.15) K were used to calculate values of C p, φ . Our results were then fitted to functions of m and T and compared to literature values.

Densities, Partial Molar Volumes, and Heat Capacities of Glycine, l-Alanine, and l-Leucine in Aqueous Magnesium Chloride Solutions at Different Temperatures

The apparent molar volumes (V2,φ) have been determined for glycine, l-alanine, and l-leucine in water and in aqueous magnesium chloride solutions with concentrations ≈ (0.05 to 0.80) mol·kg-1 by measuring the densities at (288.15, 298.15, and 308.15) K. The apparent molar heat capacities (Cp2,φ) have also been determined for glycine and l-alanine in aqueous magnesium chloride solutions with concentrations ≈ (0.05 to 0.40) mol·kg-1 by measuring heat capacities in the temperature range (298.15 to 328.15) K. These properties show a peculiar dependence upon the concentration of magnesium chloride. The standard partial molar volumes at infinite dilution ( ) obtained from these data have been used to calculate the partial molar volumes of transfer of amino acids from water to aqueous magnesium chloride solutions at infinite dilution (Δt ), which are positive for the presently studied amino acids at all temperatures and concentrations. The partial molar expansibilities (∂ /∂T)P at infinite dilution and the (∂2 /...

Heat capacities and volumes of suspensions in the presence of surfactants

Density and heat capacity measurements of water–surfactant–silica ternary systems were carried out as functions of the silica and the surfactant concentrations at 298 K. From these properties, the apparent molar volume and heat capacity of the surfactant in a given water+silica mixture were evaluated. As well, the apparent specific volume and heat capacity of silica, at a given concentration, in the water+surfactant mixtures as functions of the surfactant concentration were calculated. Some surfactants (decyltrimethylammonium bromide, sodium octanoate, sodium decanoate, sodium dodecanoate, sodium decylsulfate, sodium perfluorooctanoate and N, N-dimethyldodecylamine- N-oxide) were chosen to study the effect of the head-group and the hydrophobicity. As a general feature, the hydrophobicity of the surfactant does not essentially play a role on the silica–surfactant interactions whereas the surfactant head-group does. Finally, the apparent specific properties of silica are very sensitive in detecting the destabilization of suspensions whereas the apparent molar properties of the surfactant are not.

Apparent molar volumes and heat capacities of aqueous lithium chloride, rubidium chloride, and cesium chloride at temperatures from (278.15 to 393.15) K at the pressure 0.35 MPa

Apparent molar volumes V φ and apparent molar heat capacities C p, φ were determined for aqueous solutions of lithium chloride, rubidium chloride, and cesium chloride at molalities m=(0.02 to 1.0) mol · kg −1, and at the pressure p=0.35 MPa. Density measurements obtained with a vibrating-tube densimeter at temperatures T=(278.15 to 368.15) K were used to calculate V φ values, and heat capacity measurements obtained with a twin fixed-cell, differential-output, power-compensation, temperature-scanning calorimeter at temperatures T=(278.15 to 393.15) K were used to calculate C p, φ values. Our results were fitted to functions of m and T.

Enthalpies of Dilution of NdCl3(aq) at Temperatures from 297.89 K to 372.08 K and an Extended Pitzer Ion-Interaction Model for the NdCl3 + H2O System

Enthalpy of dilution measurements were made for NdCl3(aq) over the molality range 0.0080 mol·kg-1 to 2.6883 mol·kg-1 at temperatures from 297.89 K to 372.08 K and at a fixed pressure of 0.5 MPa. Published values of osmotic coefficients, emf's of a reversible electrochemical cell, enthalpies of dilution, apparent molar heat capacities, and apparent molar volumes of NdCl3(aq) were critically assessed, and the more reliable of these results were combined with the present enthalpies of dilution to yield the parameters of an extended form of Pitzer's ion-interaction model valid to high molalities and for the temperature range 280 K to 375 K. Values of the solubility and enthalpy of solution of the hexahydrate crystal and the enthalpy of solution of the anhydrous crystal were also included in the data representation, leading to new standard properties for the solution processes of both of these crystal phases.