Thermal behavior of n-alcohols, benzene, and toluene in water urea and water ethyleneglycol systems

Relations are suggested for calculating the heat characteristics of alcohols, benzene, and toluene in aqueous solutions of urea and ethylene glycol. The solution heat of an alcohol shows greater dependence on the glycol concentration, while the heat capacity of solution, on the urea concentration. For n-butanol in aqueous glycol, the characteristic temperature at which the solution heat of the alcohol is zero decreases as the glycol concentration increases. The dependence of the characteristic temperature of 1-butanol on the urea concentration has a maximum.     

Thermodynamics of bolaform electrolytes. V. Enthalpies and heat capacities in aqueous urea solutions

The partial molal heats of solution at infinite dilution of 1,4-bis(triethylammonium)butane dibromide and 1,10-bis(triethylammonium)decane dibromide in aqueous urea (up to 8m urea) have been determined calorimetrically in the temperature range 18–33°C. These data have been used to derive the partial molal heat capacities at infinite dilution, the enthalpies of transfer, and heat capacities of transfer at infinite dilution from water to urea-water solutions. The results show that the enthalpies of transfer are negative and decrease with increasing urea concentrations. The heat capacities of transfer are negative at low urea concentrations and increase in magnitude at higher urea concentrations. In the case of the smaller cation the partial molal heat capacity in 8m aqueous urea solution is greater than in pure water. The results are discussed in terms of structural changes in the solvents on dissolution.     

Excess molar heat capacities of (<Emphasis Type="Italic">L</Emphasis>-glutamine aqueous solution+<Emphasis Type="Italic">D</Emphasis>-glutamine aqueous solution) at temperatures between 293.15 and 303.15 K

Summary Excess molar heat capacities of (L-glutamine aqueous solution+D-glutamine aqueous solution) were determined by using a differential scanning calorimeter at temperatures between 293.15 and 303.15 K. Excess molar heat capacities are all negative. Excess molar heat capacities decrease with increasing temperature.     

Solvation of small hydrophobic molecules in formamide: A calorimetric study

The solubility and enthalpy of solution of benzene, cyclohexane, hexane, and heptane in formanide have been determined from titration microcalorimetric experiments at 25°C. The solution enthalpies are significantly more endothermic than in water but still the solubility is much higher. The entropy changes in formamide are small and positive and do not vary significantly with size. The enthalpies of solution of some 1-alkanols, 1-chloro- and 1,5-dichloropentane and pentane-1,5-diol were measured as functions of concentration. The solution enthalpies for 1-alkanols from methanol to decanol increase linearly with chain length. The enthalpic interaction coefficients h_xx are small and negative in formamide while they are large and positive in water. The partial molar heat capacities C _p,2 ^o for 1-propanol, 1-pentanol, benzene and cyclohexane in formamide were determined at 25°C from drop heat capacity measurements. Values of C _p,2 ^o are only slightly larger than the molar heat capacities of the liquid solutes.     

The solution heat and conductance of some azomethines nonaqueous solutions at 308.15 K

Some new azomethines have been synthesized and their characterization was done by IR, ¹H NMR, mass spectra and CHN analysis. Further, some physicochemical properties such as heat of solution and conductance have been studied for these synthesized compounds in different solvents at 308.15 K. The heat of solution was also determined at different temperatures.     

二元有机液体混合物热容与过剩热容的测定

溶液的热容及过剩热容是热力学的重要函数，对其测定与研究具有理论与实际意义．首先，热容是化工传热计算中的基础数据，过剩热容则可检验溶液中分子间的相互作用，并可利用其计算混合物的热容．本文报告了用法国Setaram公司生产的MS-80型Calvet微量热仪对环己酮-芳烃（苯、甲     

Enthalpies and heat capacities of transfer of sodium carboxylates and sodium dodecylsulfate from water to aqueoustert-butyl alcohol solutions

Integral enthalpies of solution at very low concentrations of sodium carboxylates and sodium dodecylsulfate in aqueous tert-butyl alcohol solutions at 25°C and 35°C were measured with an isoperibol submarine calorimeter. The enthalpies and heat capacities of transfer of these surfactants from water to aqueous tertbutyl alcohol solutions were derived from integral enthalpies of solution. The results are explained in terms of the structural alteration effect of the constituent hydrophobic and hydrophilic groups of the solute.     

Molar Volumes and Heat Capacities of Electrolytes and Ions in Nonaqueous Solvents: 1. Formamide

Apparent molar volumes and heat capacities of 27 electrolytes have been measured as a function of concentration in formamide at 25°C using a series-connected flow densimeter and Picker calorimeter system. These data were extrapolated to infinite dilution using the appropriate Debye–Hückel limiting slopes to give the corresponding standard partial molar quantities. Ionic volumes and heat capacities at infinite dilution were obtained by an appropriate assumption based on the reference electrolyte Ph₄PBPh₄ (TPTB). The ionic volumes, but not the heat capacities, agree reasonably well with previously published statistically based predictions. The values obtained are discussed in terms of simple models of electrolyte solution behavior and a number of interesting features are noted, including, possible dependencies of ionic volumes on solvent isothermal compressibility and of ionic heat capacities on solvent electron acceptor abilities.     

The Enthalpies and Heat Capacities of Solution of Tetraethyl- and Tetrabutylammonium Bromides in Methanol,Formamide, and Ethylene Glycol

The heat effects of solution of tetraethyl- and tetrabutylammonium bromides in methanol (MeOH), formamide (FA) and ethylene glycol (EG) were measured at 25 and 40°C at various concentrations. Various calculation methods were used to determine the standard enthalpies of solution. The results were compared with the available data on aqueous systems. The mean standard heat capacities of solution over the temperature range studied were calculated. The behaviors of tetraalkylammonium salts in water and FA were shown to be much less different than in water and alcohols, which was evidence of the possibility of the appearance of solvophobic solvation effects in the solution of nonpolar particles in FA.     

Heats of solution of gaseous hydrocarbons in water at 15, 25, and 35°C

Calorimetrically measured heats of solution of eleven hydrocarbon gases into water are reported at 15 and 25°C. Gases studied are methane, ethane, propane, n-butane, 2-methylpropane, 2,2-dimethylpropane, cyclopropane, ethene, propene, 1-butene, and ethyne. These values in combination with previous results are used to derive heat capacity changes at 25°C. Comparison of enthalpy and heat capacity values with those from other studies shows satisfactory agreement. Correlation of the heat capacity change with the number of water molecules in the first solvation shell of the solute suggests that the observed heat capacity changes are primarily due to changes in the water molecules in this solvent shell.     

Heat capacity and density of methylpyrrolidone solutions of sodium and potassium perchlorates at different concentrations and 298.15 K

The heat capacity and density of solutions of sodium and potassium perchlorates in N-methylpyrrolidone (MP) at 298.15 K were studied by calorimetry and densimetry. The standard partial molar heat capacities $ \bar C_{p2}^ \circ $ \bar C_{p2}^ \circ and volumes $ \bar V_2^ \circ $ \bar V_2^ \circ of NaClO₄ and KClO₄ in MP were calculated. The standard heat capacities $ \bar C_{pi}^ \circ $ \bar C_{pi}^ \circ and volumes $ \bar V_i^ \circ $ \bar V_i^ \circ of the perchlorate ion in an MP solution at 298.15 K were determined. The results are discussed with allowance for the specifics of solvation in the solutions of the salts under study. The coordination number of the ClO₄⁻ ion in an MP solution at 298.15 K was calculated.     

Isothermal and solution calorimetry to assess the effect of superplasticizers and mineral admixtures on cement hydration

The heat of hydration evolution of eight paste mixtures of various water to binder ratio and containing various pozzolanic (silica fume, fly ash) and latent hydraulic (granulated blast furnace slag) admixtures have been studied by means of isothermal calorimetry during the first 7 days of the hydration process and by means of solution calorimetry for up to 120 days. The results of early heat of hydration values obtained by both methods are comparable in case of the samples without mineral admixtures; the values obtained for samples containing fly ash and granulated blast furnace slag differ though. The results from isothermal calorimetry show an acceleration of the hydration process by the presence of the fine particles of silica fume and retarding action of other mineral admixtures and superplasticizer. The influence of the presence of mineral admixtures on higher heat development (expressed as joules per gram of cement in mixture) becomes apparent after 20 h in case of fly ash without superplasticizer and after 48 h for sample containing fly ash and superplasticizer. In case of samples containing slag and superplasticizer the delay observed was 40 h. The results obtained by solution calorimetry provide a good complement to the ones of isothermal calorimetry, as the solution calorimetry enables to study the contribution of the mineral admixtures to the hydration heat development at later ages of the hydration process, which is otherwise hard to obtain by different methods.     

Heats of dilution of trialkyl phosphates in iso-octane and carbon tetrachloride: Interpretation in terms of self-association

The heats of solution and dilution of triethyl phosphate (TEP), tripropyl phosphate (TPP), and tributyl phosphate (TBP) in iso-octane have been measured at 25°C. The enthalpy of dilution was found to decrease with hydrocarbon chain length. The resulting apparent molal heat content, φ_L, values are interpreted in terms of the degree and nature of the associated species present assuming that the heat of dilution is essentially due to the breakdown of the various associated species. The results are consistent with a monomer-to-dimer model. Equilibrium constants and enthalpy change values are calculated for the dimerization reaction. The heat of dilution of TBP in carbon tetrachloride was exothermic rather than endothermic, indicating significant solute-solvent interaction.     

Sorption equilibrium of methanol on new composite sorbents “CaCl<Subscript>2</Subscript>/silica gel”

This paper presents experimental data on methanol sorption on new composite sorbents which consist of mesoporous silica gels and calcium chloride confined to their pores. Sorption isobars and XRD analysis showed the formation of a solid crystalline solvate CaCl₂⋅2MeOH at low methanol uptake, while at higher uptake the formation of the CaCl₂–methanol solution occurred. The solution confined to the silica pores showed the sorption properties similar to those of the CaCl₂–methanol bulk solution. Calorimetric and isosteric analyses showed that the heat of methanol sorption depends on the methanol uptake, ranging from 38±2 kJ/mol for the solution to 81±4 kJ/mol for the solid crystalline phase CaCl₂⋅2MeOH. The above mentioned characterizations allowed the evaluation of the methanol sorption and the energy storage capacities, clearly showing that the optimal applications of these new composite sorbents are the methanol removal from gaseous mixtures, heat storage and sorption cooling driven by low temperature heat.     

Enthalpy and heat capacity parameters of ammonium bromide interaction with hexamethylphosphotriamide in water

Thermal effects of solution of ammonium bromide in hexamethylphosphotriamide (HMPT)-water mixtures at 4° C, 15°C, and 46°C in the region of minor additions of the nonaqueous component were investigated for the first time by calorimetry. Variations of heat capacity in the course of solution were calculated using previous data for 25°C and 40°C. The curves of the heat capacity of solution (transfer) and temperature variation of transfer entropy versus composition have a minimum near the region of the existence of the 1:20 HMPT:water clathrate. The enthalpy, heat capacity, and temperature variations of the entropy coefficients of electrolyte amide pair and three-particle interactions in water were calculated in terms of MacMillan-Mayer theory. Within the framework of the group additivity method it is shown that the heat capacity coefficient of the bromide ion-HMPT pair interaction is negative and dictates temperature variations of enthalpy for ammonium bromide and tetraalkylammonium interactions with HMPT in water.     

Thermodynamic Properties of Salsoline Salsolinodithiocarbamate

Heat of solution of salsoline salsolinodithiocarbamate (SS) at 1 : 18 000, 1 : 36 000, and 1 : 72 000 dilution (mol per mol H₂O) was determined on a DAK-I-IA calorimeter, and the standard heat of solution at infinite dilution was estimated. The temperature dependence of the heat capacity of SS was studied over the range 173–348 K. The heats of combustion and fusion, and the standard heat of formation of liquid (molten) and crystalline SS were estimated by indirect methods.     

Determination of unfrozen matrix concentrations at low temperatures using stepwise DSC

The aim of the current study was to determine whether stepwise DSC (SW-DSC) is a suitable method for measuring the unfrozen matrix concentration (C_g) of binary aqueous solutions at temperatures as low as −50 °C. The optimal experimental conditions were determined using water. Reliable heat capacity values were determined at nominal scanning rates between 10 and 100 K min⁻¹, sample weights between 8 and 15 mg, and with the sample completely covering the base of the DSC pan. These conditions were then applied to aqueous solutions of ethylene glycol, glycerol and sodium chloride.The apparent heat is the sum of all heat including latent heat, heat capacity and heat of dilution. The influence of each term on the apparent heat was discussed in detail. The apparent heat values of the frozen samples were then used to calculate the ice fraction in the solution and were expressed as the C_g. The calculated C_g values were similar to previously published values. This study showed that SW-DSC can be used to determine the C_g over a wide temperature range using only one single solution. This technique is advantageous for solutes that are not available in large quantities.     

A novel method for estimation of transition temperature for polymorphic pairs in pharmaceuticals using heat of solution and solubility data

A novel method for thermodynamic stability studies of polymorphic drug substances has been developed. In order to estimate the transition temperature for an enantiotropic polymorphic pair, a formula for calculating the temperature at which the solubilities of each polymorph become equal has been derived with heat of solution and solubility as the variables. This formula is based on the assumption that van't Hoff plots (logarithmic solubility versus reciprocal of absolute temperature plots) of each polymorph show a straight line (heat of solution is independent of temperature) whose slope can be expressed as a function of heat of solution. The transition temperatures for seratrodast, acetazolamide and carbamazepine polymorphic pairs calculated by the formula were in good agreement with the results of previous studies. Furthermore, the calculated transition temperature for the indomethacin polymorphic pair was above the melting point, an unrealistic temperature range, suggesting that these polymorphs are monotropically related. Since this formula requires solubility data at only one arbitrary temperature other than heat of solution data for both polymorphs in a polymorphic pair, the proposed method is much faster than the conventional method requiring solubility data at five or more different temperatures for the preparation of van't Hoff plots.     

A new tool for an old job: Using fixed cell scanning calorimetry to investigate dilute aqueous solutions

The development of fixed twin cell temperature scanning calorimeters has enabled the more efficient determination of heat capacities of dilute aqueous solutions with a precision comparable to that of the Picker flow heat capacity calorimeters developed nearly 40 years ago. Experiments require less than 0.5 cm³ of solution, and results can be obtained routinely over the temperature range (278 to 395) K at pressures up to a few bars. Multiple scanning of samples by both increasing and decreasing temperature allows assessment of instrument drift, solute stability, and reproducibility of results. Chemical calibration is essential to take full advantage of the precision and sensitivity of the calorimeters. The calorimetric output is a direct measure of the difference in heat capacity per unit volume of a solution and of a reference liquid, usually water. Thus, densities of the solution and reference liquid are needed to transform the results into heat capacities per unit mass of solution. Examples of solutes that have been investigated include a variety of inorganic and organic compounds that dissolve to give simple ionic or neutral species, or that produce complexes or species that exist in equilibrium distributions that can change as the temperature is scanned. Appropriate selection of the results from experiments on combinations of solutes allows calculation of standard state (zero concentration) thermodynamic quantities for chemical processes and reactions over the ranges of temperature scanned at the solution compositions investigated. Results for a few specific systems are presented and discussed for some representative classes of solutes that have been investigated in our laboratory since 1998.     

The Partial Molar Volume and Heat Capacity of the Glycyl Group in Aqueous Solution at 25^C

The partial molar volumes, V₂ ^{^}, and the partial molar heat capacities, C_p,2 ^{^}, at infinite dilution have been determined for three new peptides of sequence seryl(glycyl)_xglycine, where x=0 to 2, in aqueous solution at 25^{^}C. Values for V₂ ^{^} at 25^°C have also been determined for two neutral peptide derivatives N-acetylglycylglycinamide and N-acetylglycylglycylglycinamide. These V₂ ^°; and C_p,2 ^°; results were used to estimate the partial molar volume and heat capacity of the backbone glycyl group, CH₂CONH, of proteins in aqueous solution at 25^°;C. The results obtained are compared with those calculated using partial molar data for alternative model compounds. The new glycyl group contributions are in excellent agreement with those currently used in our group additivity schemes for the calculation of the partial molar volumes and heat capacities of unfolded proteins.