Standard Partial Molar Heat Capacities Research Articles

Effect of the Temperature on the Process of Preferential Solvation of 1,4-Dioxane, 12-Crown-4, 15-Crown-5 and 18-Crown-6 Ethers in the Mixture of N-Methylformamide with Water: Composition of the Solvation Shell of the Cyclic Ethers.

The aim of the work was to analyze the preferential solvation process, and determine the composition of the solvation shell of cyclic ethers using the calorimetric method. The heat of solution of 1,4-dioxane, 12-crown-4, 15-crown-5 and 18-crown-6 ethers in the mixture of N-methylformamide with water was measured at four temperatures, 293.15 K, 298.15 K, 303.15 K, and 308.15 K, and the standard partial molar heat capacity of cyclic ethers has been discussed. 18-crown-6 (18C6) molecules can form complexes with NMF molecules through the hydrogen bonds between -CH3 group of NMF and the oxygen atoms of 18C6. Using the model of preferential solvation, the cyclic ethers were observed to be preferentially solvated by NMF molecules. It has been proved that the molar fraction of NMF in the solvation shell of cyclic ethers is higher than that in the mixed solvent. The exothermic, enthalpic effect of preferential solvation of cyclic ethers increases with increasing ring size and temperature. The increase in the negative effect of the structural properties of the mixed solvent with increase in the ring size in the process of preferential solvation of the cyclic ethers indicates an increasing disturbance of the mixed solvent structure, which is reflected in the influence of the energetic properties of the mixed solvent.

Composition of the Solvation Shell of the Selected Cyclic Ethers (1,4-Dioxane, 12-Crown-4, 15-Crown-5 and 18-Crown-6) in a Mixture of Formamide with Water at Four Temperatures

The solution enthalpy of 15-crown-5 and 18-crown-6 ethers in the mixture of formamide (F) and water (W) was measured at four temperatures: 293.15 K, 298.15 K, 303.15 K, 308.15 K. The standard molar enthalpy of solution, ΔsolHo, depends on the size of cyclic ethers molecules and the temperature. With increasing temperature, the values of ΔsolHo become less negative. The values of the standard partial molar heat capacity Cp,2o of cyclic ethers at 298.15 K have been calculated. The Cp,2o=f(xW) curve shape indicates the hydrophobic hydration process of cyclic ethers in the range of a high-water content in the mixture with formamide. The enthalpic effect of preferential solvation of cyclic ethers was calculated and the effect of temperature on the preferential solvation process was discussed. The process of complex formation between 18C6 molecules and formamide molecules is observed. The cyclic ethers molecules are preferentially solvated by formamide molecules. The mole fraction of formamide in the solvation sphere of cyclic ethers has been calculated.

Standard Partial Molar Heat Capacities and Volumes of Aqueous N,N-Dimethylethanolamine and N,N-Dimethylethanolammonium Chloride from 283.15 to 393.15 K, and Ionization Constants to 598.15 K

Standard Partial Molar Heat Capacities and Volumes of Aqueous <i>N</i>,<i>N</i>-Dimethylethanolamine and <i>N</i>,<i>N</i>-Dimethylethanolammonium Chloride from 283.15 to 393.15 K, and Ionization Constants to 598.15 K

Enthalpies and heat capacities of solution of 3,5-diamino-1,2,4-triazole and 3,5-diamino-1-phenyl-1,2,4-triazole in water

This paper focuses on the thermochemical behavior of two derivatives of 1,2,4-triazole which is often considered as a potential synthetic platform to develop novel antitumor or antimicrobial drugs, i.e., 3,5-diamino-1,2,4-triazole (compound 1) and 3,5-diamino-1-phenyl-1,2,4-triazole (compound 2). Experimental enthalpies of solution in water have been determined calorimetrically over the physiological temperature range. These quantities are used to compute standard enthalpies and heat capacities of solution. Standard partial molal heat capacities of solution are calculated from the heat capacities of solution and experimentally determined heat capacities of solid heterocycles. The results obtained are compared with those for hydrophilic urea and hydrophobic benzene and briefly discussed.

Heat Capacity and Volume Properties of Ammonium Thiocyanate in N-Methylpyrrolidone Solution at 298.15 K

The heat capacity and volumetric properties of ammonium thiocyanate solutions in N-methylpyrrolidone are measured at 298.15 K by calorimetric and densimetric means. Concentration dependences of the partial and apparent molar heat capacities and volumes of the investigated systems are discussed. The standard partial molar heat capacity and volume of NH4CNS, and the standard heat capacity and volume of ammonium and thiocyanate ions in N-methylpyrrolidone at 298.15 K are calculated.

Standard Partial Molar Heat Capacity and the Volume of the Cadmium Ion in Acetonitrile at 298.15 K

The heat capacity and volumetric properties of cadmium iodide solutions in acetonitrile (AN) are measured at 298.15 K by calorimetric and densimetric means. Standard partial molar heat capacity $$\bar {C}_{{p,2}}^{^\circ }$$ and volume $$\bar {V}_{2}^{^\circ }$$ of CdI2 in AN are calculated. Standard heat capacity $$\bar {C}_{{p,i}}^{^\circ }$$ and volume $$\bar {V}_{i}^{^\circ }$$ of the cadmium ion in AN at 298.15 K are determined. The effect produced by the nature of such solvents as AN, DMF, DMSO, and MP on $$\bar {C}_{{p,i}}^{^\circ }$$ and $$\bar {V}_{2}^{^\circ }$$ of the cadmium ion is analyzed, and a substantial contribution from the electrostatic component is discovered.

Standard Partial Molar Heat Capacities and Volumes of Barium and Cadmium Ions in Dimethylformamide at 298.15 K

The heat capacity and bulk properties of barium and cadmium iodide solutions in dimethylformamide (DMF) at 298.15 K are measured via calorimetry and densimetry. Standard partial molar heat capacities $$\bar {C}_{{p,2}}^{^\circ }$$ and volumes $$\bar {V}_{2}^{^\circ }$$ ВаI2 and CdI2 in DMF are calculated. The standard values of heat capacity $$\bar {C}_{{p,i}}^{^\circ }$$ and volume $$\bar {V}_{i}^{^\circ }$$ of barium and cadmium in DMF at 298.15 K were determined.

Standard Partial Molar Heat Capacities and Volumes of Barium and Cadmium Ions in Dimethylsulfoxide at 298.15 K

The heat capacities and volumes of dimethylsulfoxide (DMSO) solutions of barium and cadmium iodides at 298.15 K were measured by calorimetry and densimetry. The standard partial molar heat capacities $$\bar {C}_{{p,2}}^{^\circ }$$ and volumes $$\bar {V}_{2}^{^\circ }$$ of BaI2 and CdI2 in DMSO were calculated. The standard heat capacities $$\bar {C}_{{p,i}}^{^\circ }$$ and volumes $$\bar {V}_{i}^{^\circ }$$ of barium and cadmium ions in DMSO at 298.15 K were determined.

Thermodynamics of solution of L-valine in water

This paper focuses on the accurate thermodynamic study of solution of L-valine in water in a wide temperature range. Enthalpies of solution of L-valine in water have been calorimetrically determined between T=279K and T=323 К. Standard enthalpies and heat capacities of solution as well as standard partial molal heat capacities have been calculated and compared with available literature values. The free energy of solution and its enthalpic and entropic terms have been computed using the combination of solubility and calorimetric data via the Gibbs-Helmholtz equation from T=280K to T=360K. The temperature dependence of solubility of the amino acid has been also computed and compared with experimental quantities. The satisfactory agreement is found between experimental and predicted solubility values.

Standard partial molar heat capacities and volumes of aqueous N-methylpiperidine and N-methylpiperidinium chloride from 283 K to 393 K

Densities and volumetric heat capacities for dilute solutions of N-methylpiperidine (N-MP, 0.2mol·kg−1) and N-methylpiperidinium chloride (N-MPH+Cl−, 0.1mol·kg−1) were measured relative to water at 0.1MPa using a vibrating-tube densimeter, and at 0.4MPa using a twin fixed-cell, power-compensation, differential temperature-scanning nano calorimeter, over the temperature ranges 283.15K≤T≤363.15K and 283.15K≤T≤393.15K, respectively. The resulting apparent molar volumes, Vϕ, and heat capacities, Cp,ϕ, were corrected for speciation effects using Young’s rule and extrapolated to infinite dilution using the Debye-Hückel limiting law, Yo≈Yϕ−AYIs1/2, to yield the standard partial molar properties, Yo, for N-MP(aq) and N-MPH+Cl−(aq). The standard partial molar volumes, Vo, and heat capacities, Cpo, were represented by a semi-empirical function of solvent density and temperature, Yo(ρw,T), the “density” model, which can be used to extrapolate these results, as well as other thermodynamic properties for the ionization of N-methylpiperidine, to higher temperatures.

Thermodynamics of aqueous adenine: Standard partial molar volumes and heat capacities of adenine, adeninium chloride, and sodium adeninate from T = 283.15 K to 363.15 K

Apparent molar volumes, Vϕ, and apparent molar heat capacities, Cp,ϕ, were measured for aqueous solutions of neutral adenine (AdH) and adeninium chloride (AdH2Cl) at temperatures from 288.15K to 363.15K, and for sodium adeninate (NaAd) at temperatures from 283.15K to 313.15K. Density measurements used in the determination of the standard partial molar volume, Vo, were made with a vibrating-tube densimeter at ambient pressure. Heat capacity measurements used in the determination of the standard partial molar heat capacity, Cpo, were made with a twin fixed-cell, differential output, power compensating, temperature-scanning calorimeter at a pressure of 0.4MPa. The contributions from minor equilibrium species were removed using Young’s Rule to yield values for the standard partial molar volume and heat capacities of the ionic species AdH2+(aq) and Ad−(aq), and the equilibrium mixture of neutral species AdH∗(aq). Semi-empirical equations describing the temperature dependence of Vo and Cpo for each species were fitted by regression to the experimental results. From these equations, the standard partial molar volume change ΔrVom and heat capacity change ΔrCpom for the ionization reactions were calculated. The standard partial molar volumes presented in this study for neutral adenine are the first to be experimentally determined at temperatures above 330K, while the standard partial molar heat capacities are the first to be reported at temperatures above 298.15K. The experimental values for the adeninium cation and adeninate anion are the first to be reported in the literature.

Ionization Constants of DL-2-Aminobutyric Acid and DL-Norvaline Under Hydrothermal Conditions by UV–Visible Spectroscopy

The first and second ionization constants for the amino acids DL-2-aminobutyric acid (DL-2-aminobutanoic acid) and DL-norvaline (DL-2-aminopentanoic acid) were determined under hydrothermal conditions, from 175 to 275 °C at 10 MPa, using thermally-stable colorimetric pH indicators (acridine, 4-nitrophenol and 2-naphthoic acid). The measurements were carried out by UV–visible spectroscopy using a high-temperature, high-pressure platinum flow cell with sapphire windows, which minimized the effects of thermal decomposition. The results were combined with literature values from titration calorimetry at 25–130 °C to yield an extended van’t Hoff model for the temperature dependence of the ionization constants for the carboxylic acid and ammonium groups, \( K_{\text{a,COOH}} \) and \( K_{{{\text{a,NH}}_{3}^{ + } }} \), over the entire temperature range. The experimental results for the second ionization constant \( K_{{{\text{a,NH}}_{3}^{ + } }} \) at elevated temperatures are consistent with the predictions from the Yezdimer–Sedlbauer–Wood functional group additivity model, but for the first ionization constant \( K_{\text{a,COOH}} \) are not. This suggests that the group contribution parameters for the standard partial molar heat capacity of the carboxylic acid group are in error, or that nearest neighbor interactions between the –COOH and \( - {\text{NH}}_{3}^{ + } \) groups cause a breakdown in the functional group additivity relationship.

Heat capacity and density of potassium iodide solutions in mixed N-methylpyrrolidone-water solvent at 298.15 K

The heat capacity and density of potassium iodide solutions in a mixed N-methylpyrrolidone (MP)-water solvent with a low content of the organic component are measured via calorimetry and densimetry at 298.15 K. Standard partial molal heat capacities \(\bar C_{p,2}^ \circ \) and volumes \(\bar V_2^ \circ \) of potassium iodide in MP-water mixtures are calculated. Standard heat capacities \(\bar C_{p,i}^ \circ \) and volumes \(\bar V_i^ \circ \) of potassium and iodide ions are determined. The character of the changes in heat capacity and volume are discussed on the basis of calculating additivity coefficients δc and δv upon the mixing of isomolal binary solutions KI-MP and KI-water, depending on the composition of the MP-H2O mixture and the concentration of the electrolyte.

Standard partial molar heat capacities and enthalpies of formation of aqueous aluminate under hydrothermal conditions from integral heat of solution measurements

Heats of solution of sodium aluminum oxide, NaAlO2(s), were measured in aqueous sodium hydroxide solutions using a Tian–Calvet heat-flow calorimeter (Setaram, Model C80) with high pressure “batch cells” made of hastelloy C-276, at five temperatures from (373.15 to 523.15)K, steam saturation pressure, and concentrations from (0.02 to 0.09)mol·kg−1. Standard molar enthalpies of solution, ΔsolnH∘, and relative standard molar enthalpies, [H∘(T)−H∘(298.15K)], of NaAl(OH)4(aq) were determined from the measured heats of solution. The results were fitted with the “density” model. The temperature dependence of ΔsolnH∘ from the model yielded the standard molar heat capacities of reaction, ΔsolnCp∘, from which standard partial molar heat capacities for aqueous aluminate, Cp∘[A1(OH)4−,aq], were calculated. Standard partial molar enthalpies of formation, ΔfH∘, and entropies, S∘, of A1(OH)4−(aq) were also determined. The values for Cp∘[A1(OH)4−,aq] agree with literature data determined up to T=413K from enthalpy of solution and heat capacity measurements to within the combined experimental uncertainties. They are consistent with differential heat capacity measurements up to T=573K from Schrödle et al. (2010) [29] using the same calorimeter, but this method has the advantage that measurements could be made at much lower concentrations in the presence of an excess concentration of ligand. To our knowledge, these are the first standard partial molar heat capacities measured under hydrothermal conditions by the integral heat of solution method in a commercial calorimeter to be reported in the literature.

Ion-molecular interactions in solutions of potassium and cadmium thiocyanates in N-methylpyrrolidone at 298.15 k, according to calorimetry and densitometry data

The heat capacity and density of KNCS-N-methylpyrrolidone (MP), Cd(NCS)2-MP, and KNCS-Cd(NCS)2-MP solutions at 298.15 K are studied by means of calorimetry and densitometry. Standard partial molar heat capacities and volumes (\(\bar C^\circ _{p,2} \) and \(\bar V^\circ _2 \)) of the studied electrolytes in MP are calculated. Standard values of heat capacity \(\bar C^\circ _{p,i} \) and volume \(\bar V^\circ _i \) of NCS− ions in MP at 298.15 K are determined. Values of the heat capacity and volume changes upon the formation of the three-component system KNCS-Cd(NCS)2-MP from binary solutions are obtained and discussed.

Heat capacity and density of solutions of calcium and cadmium nitrates in N-methylpyrrolidone at 298.15 K

The heat capacity and density of solutions of calcium and cadmium nitrates in N-methylpyrrolidone (MP) at 298.15 K are studied by calorimetry and densimetry. The obtained data are discussed in relation to certain features of solvation and complex formation in solutions of these salts. The standard partial molar heat capacities and volumes (\(\overline {C_{p^2 }^0 }\) and \(\overline {V_2^0 }\)) of the electrolytes in MP are calculated. The standard heat capacities \(\overline {C_{p^i }^0 }\) and volumes \(\overline {V_i^0 }\) of Ca2+ and Cd2+ ions in MP at 298.15 K were determined, along with the contribution from specific interactions to the values of \(\overline {C_{p^i }^0 }\) and \(\overline {V_i^0 }\) of Cd2+ ions in MP solution.

Calculating the standard values of the heat capacity of alkaline metal ions and iodide ions in a mixed N-methylpyrrolidone-water solvent at 298.15 K

A system of ionic components of \(\bar C_{p,i}^0 \) is proposed for the standard partial molar heat capacities \(\bar C_{p2}^0 \) of electrolytes in a mixed N-methylpyrrolidone (MP)-water solvent. The \(\bar C_{p,i}^0 \) values are calculated for Li+, Na+, K+, Rb+, Cs+, and I− ions in a mixed MP-water solvent at 298.15 K. The individual components of \(\bar C_{p,i}^0 \) values and their dependence on the solvent composition and ion size are considered.

Densities, Specific Heat Capacities, Apparent and Partial Molar Volumes and Heat Capacities of Glycine in Aqueous Solutions of Formamide, Acetamide, and N,N-Dimethylacetamide at T=298.15 K and Ambient Pressure

Apparent molar volumes (V 2,φ ) and heat capacities (C p2,φ) of glycine in known concentrations (1.0, 2.0, 4.0, 6.0, and 8.0 mol⋅kg−1) of aqueous formamide (FM), acetamide (AM), and N,N-dimethylacetamide (DMA) solutions at T=298.15 K have been calculated from relative density and specific heat capacity measurements. These measurements were completed using a vibrating-tube flow densimeter and a Picker flow microcalorimeter, respectively. The concentration dependences of the apparent molar data have been used to calculate standard partial molar properties. The latter values have been combined with previously published standard partial molar volumes and heat capacities for glycine in water to calculate volumes and heat capacities associated with the transfer of glycine from water to the investigated aqueous amide solutions, $\Delta\overline{V}_{\mathrm{2,tr}}^{\mathrm{o}}$ and $\Delta\overline{C}_{p\mathrm{2,tr}}^{\mathrm{o}}$ respectively. Calculated values for $\Delta\overline{V}_{\mathrm{2,tr}}^{\mathrm{o}}$ and $\Delta\overline{C}_{p\mathrm{2,tr}}^{\mathrm{o}}$ are positive for all investigated concentrations of aqueous FM and AM solutions. However, values for $\Delta\overline{C}_{p\mathrm{2,tr}}^{\mathrm{o}}$ associated with aqueous DMA solutions are found to be negative. The reported transfer properties increase with increasing co-solute (amide) concentration. This observation is discussed in terms of solute + co-solute interactions. The transfer properties have also been used to estimate interaction coefficients.

Concentration dependences of the heat capacity of solutions of alkali metal iodides in N-methylpyrrolidone-water mixed solvent at 298.15 K

Heat capacities of solutions of alkali metal iodides (MeI) in N-methylpyrrolidone (MP)-water mixed solvent were measured over the range of compositions. The influence of the composition of the mixed solvent on the heat capacity of MeI-MP-H2O ternary systems is discussed. Standard partial molar heat capacities \( \bar C_{p_2 }^o \) (MeI) in the MP-water mixed solvent at 298.15 K are calculated.

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 \( \bar C_{p2}^ \circ \) and volumes \( \bar V_2^ \circ \) of NaClO4 and KClO4 in MP were calculated. The standard heat capacities \( \bar C_{pi}^ \circ \) and volumes \( \bar V_i^ \circ \) 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.