Heat Capacities Of Solutions Research Articles

Nonprimitive Model Electrolyte Solutions: Comprehensive Data from Monte Carlo Simulations

We report molecular simulation data for the Helmholtz energy, the internal energy, and the constant-volume heat capacity of nonprimitive model electrolyte solutions, that is, mixtures of charged and nonpolarizable dipolar hard spheres. We consider model electrolyte solutions where positively and negatively charged particles and the dipolar solvent particles all have the same hard-sphere diameter. For a range of dimensionless density, 0.05 ≤ ρ* ≤ 1.0, we consider fluids with dimensionless dipole moments up to μ*2 ≤ 4. The dimensionless charge has a range of 25 ≤ q*2 ≤ 150, and the total mole fraction of ions covers a range of 0.002 ≤ x ≤ 0.12.

Calorimetric and small-angle X-ray scattering studies on the memory effect in the tetra-n-butylammonium bromide semiclathrate hydrate system

Abstract The solution structures in the tetra-n-butylammonium bromide (TBAB) aqueous solution relate closely with the memory effect. In the present study, the behavior derived from the existence of the residual solution structures after TBAB semiclathrate hydrate (TBAB SCH) decomposition was investigated with two methods. One is a high-precision differential scanning calorimetry. The heat capacity of a TBAB aqueous solution with memory effect was slightly larger than that after the memory effect disappeared. The larger heat capacity implies the existence of solution structures. The other is a small-angle X-ray scattering (SAXS). In the first cooling process, strong scattering derived from rapid crystallization was observed at 263.6 K. In the second cooling process where the TBAB aqueous solution exhibited the memory effect, the scattering intensity gradually increased and became remarkably strong at a temperature (approximately 277 K) higher than 263.6 K. In the second cooling process, the invariant Q, which corresponds to electron density fluctuation, increased gradually until crystallization, whereas, in the first cooling process, the change of the invariant Q was quite small until crystallization. The increase of invariant Q implies the existence of 10–100 nm density fluctuation, which is consistent with the cluster size (10–20 nm) previously observed with electron microscopy in the same system.

Structural stability and mechanical property of Fe-W solid solutions from a constructed Fe-W potential

An Fe-W potential has been constructed by means of the embedded-atom method and has proven to be more realistic than the three published Fe-W potentials in the literature. Based on the constructed Fe-W potential, molecular dynamic simulation has been used to reveal structural stability, thermodynamic properties, and mechanical properties of BCC Fe-W solid solutions within the entire composition range. It is found that the Fe-W interaction in BCC Fe-W solid solutions should be weak and attractive with small and negative heats of formation, which agree well with those from the thermodynamic Miedema model and could clarify the controversy regarding heats of formation of Fe-W solid solutions in the literature. In addition, the derived coefficient of thermal expansion, heat capacity, elastic constants, and elastic moduli of Fe-W solid solutions from the present Fe-W potential are in good agreement with the corresponding data from ab initio calculation or experiments in the literature.

Thermodynamically Traceable Calorimetric Results for Dilute Aqueous Potassium Chloride Solutions at Temperatures from 273.15 to 373.15 K. Part 2. The Quantities Associated with the Partial Molar Heat Capacity

In previous articles (Partanen J. Chem. Eng. Data 2019, 64, 16−33 and Partanen J. Chem. Eng. Data 2019, 64, 2519–2535), we presented traceable and transparent two-parameter Hückel equations (with parameters B and b1) for the activity coefficients of the salt and for the osmotic coefficients of water in aqueous KCl solutions in the temperature range of 273.15–383.15 K. The latter article is the first part (Part 1) of the calorimetric study. We showed in these articles that our equations for these solutions explain within experimental error the literature data on almost all thermodynamic quantities including the partial molar enthalpies at least up to a molality of 0.2 mol·kg–1 and up to 373 K. In this model, parameter B is regarded as a constant but parameter b1 has a quadratic temperature dependence. No calorimetric data were needed in the parameter estimation. In the second part (Part 2) of the calorimetric study, now, the results obtained for the heat capacity quantities of KCl (aq.) are considered. We show here that all heat capacity literature available for KCl solutions at least up to 0.5 mol·kg–1 is possible to explain within experimental error using exactly the same Hückel equations as those considered previously in our studies for dilute KCl solutions from 273 to 373 K. Because of the success of the used model, we supplement the existing thermodynamic tables with new values for the relative apparent and partial molar heat capacities for KCl solutions. It is likely that the new tables contain the most reliable values available for these heat capacity quantities.

Thermodynamics and Structure of Micelles in Aqueous Solutions of Sodium Decyl Sulfate in the Region of the Third Critical Micelle Concentration

Using data on heat capacity of sodium decyl sulfate solutions near the third critical micelle concentration, obtained earlier via high-precision scanning calorimetry, the temperature dependences are calculated for the thermodynamic functions of the corresponding micellar transition and the components of its Gibbs free energy. It is shown that the considered intermicellar transition, interpreted as the micellar shape transforming from cylindrical to lamellar as the concentration grows, occurs at an equilibrium molality of 0.33 and a temperature of 323 K. Correlations between the thermodynamic functions of the transition with structural changes in the micelles and the key micellar parameters are discussed.

Heat of Absorption of CO2 and Heat Capacity Measurements in Aqueous Solutions of Benzylamine, N-(2-Aminoethyl)-ethanolamine, and Their Blends Using a Reaction Calorimeter

In this study, the heats of absorption of CO2 in aqueous benzylamine (BZA), N-(2-aminoethanolamine) (AEEA), and their blends were measured using an automated reaction calorimeter in the temperature range of 303.15–343.15 K. The experimental concentrations of aqueous amine solutions were in the range of (0.49–4.0) mol BZA·kg–1 water, (0.51–4.11) mol AEEA·kg–1 water, (2.03 mol BZA + 2.09 mol AEEA)·kg–1 water, and (2.71 mol BZA + 1.39 mol AEEA)·kg–1 water. The heat capacities of the unloaded aqueous solutions of BZA, AEEA, and (BZA + AEEA) were also measured in similar temperature and concentration ranges to those for heat of absorption. The experimental heat of absorption of CO2 was presented as a function of CO2 loading, temperature, and amine concentration.

Solvation and ion–ion interactions in aqueous and non-aqueous solutions of cationic cytostatic agent prospidium chloride

The thermochemical behavior of well-established heterocyclic anticancer drug, prospidium chloride, was comparatively evaluated in water and two other non-aqueous solvents, formamide and ethylene glycol, forming the three dimensional H-bond network. Standard enthalpies and heat capacities of solution, as well as, enthalpic parameters of solute–solute pair interactions were estimated at 298 and 318 K and compared with the available values for some ionic species. A linear correlation between the energetics of ion–ion interactions and the reciprocal dielectric constant of the medium for tetraethylammonium bromide and prospidium chloride was revealed.

Isobaric Heat Capacity of Ionic Liquids in Aqueous Solutions. A Review

A review of the available literature data for heat capacity of room temperature ionic liquid aqueous solutions is presented. To show at what extent their behavior departs from that of the ideal mixture, excess and apparent heat capacities are calculated. A comparison between different systems is made in order to elucidate the main factors that affect heat capacity behavior. The experimental results are also compared with available heat capacity data for salts and molecular compounds. Large deviations from ideality appear at low ionic liquid mole fraction. It is found that this nonideal behavior resembles, for most studied systems, that of molecular systems characterized by large hydrophobic domains. The appearance of pseudomicellar structures in diluted ionic liquid solutions seems to be the origin of the anomalies in the behavior of heat capacity.

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.

Two-point scaling analysis of the isobaric heat capacity of dodecyltrimethylammonium bromide aqueous solutions in the presence of the n-hexan-1-ol as a co-surfactant

The specific heat capacities at constant pressure cp of aqueous solutions of cationic surfactant: dodecyltrimethylammonium bromide, with addition of co-surfactant: n-hexan-1-ol with the molar ratio of surfactant to co-surfactant 1:1 have been measured within temperature range (278.15–328.15) K over wide concentration range. The apparent and partial molar heat capacities of the surfactant/co-surfactant were calculated to analyse the aggregation process taking place in the solution. In order to study some additional information on the solution structure and verify the shape of the aggregates the two-point scaling theory was used for the first in the case of the surfactant/co-surfactant system in which prolate micelles are formed.

Properties of Micellar Solutions of Sodium Decyl Sulfate at Relatively High Concentrations

Heat capacities of aqueous solutions of anionic surfactant sodium decyl sulfate in the 0.28–0.42 mol kg−1 range of molar concentrations and the 278–363 K range of temperatures are studied via precision adiabatic differential scanning microcalorimetry. Specific and apparent heat capacities of solutions at intervals of 0.01 mol kg−1, partial molar heat capacities of the solute and the solvent, and excess partial molar heat capacities are plotted as functions of concentration and temperature. The Kraft boundary is determined. Analysis of the characteristic changes in the above properties reveals structural changes in sodium decyl sulfate micelles that correspond to their shape transforming from cylindrical to plate-like in the region of the third critical micelle concentration.

The Structure of Polymer Clusters in Aqueous Solutions of Hydroxypropyl Cellulose

The viscosity, turbidity, and heat capacity of dilute aqueous solutions of hydroxypropyl cellulose have been studied in a concentration interval of 0.047–1.5 g/l and a temperature interval of 20–80 ∘C. The data obtained testify that, if the temperature does not exceed 40 ∘C, hydroxypropyl cellulose molecules are prolate spheroidal globules with semiaxis lengths of 7 and 490 ˚ A. At temperatures above 70 ∘C, the hydroxypropyl cellulose solution consists of clusters; every cluster is composed of 11 globules and has a prolate spheroidal form with semiaxes of 41 and 490 ˚ A. In the temperature interval from 40 to 70 ∘C, the solution concerned contains both globules and clusters, with the concentration of the latter increasing, as the temperature grows.

Thermal energy analysis on liquid desiccant air conditioning system at different desiccant solution parameters

Selection of suitable liquid desiccant operating parameters plays a significant role in the design of energy efficient liquid desiccant air conditioning system. To achieve same dehumidification rate from ambient air, different combinations of solution parameters (heat capacity ratio, concentration, and vapor pressure) could be employed in the system. Considering dehumidifier air inlet condition and dehumidification rates are fixed, an analytical study is carried out on the thermal energy analysis of the system at different solution operating parameters. Operating parameters considered in this study are solution concentrations ( Cs = 0.25, 0.3, 0.35 and 0.40) and heat capacity ratios ([Formula: see text] = 2.5, 3, 4 and 5). Control volume which includes a pair of air and solution channels (half width channels) of full scale liquid-to-air membrane energy exchangers (LAMEE) has been chosen to analyze the energy transfer between air and solution. The results indicate system requires lesser chiller load ( Qchiller) at high concentration and low heat capacity ratio ( Cs = 0.40 and [Formula: see text] = 2.5) which is 0.29 kW to achieve 0.61 kW cooling load. This is 99% lesser than the Qchiller at high concentration and high heat capacity ratio ( Cs = 0.40 and [Formula: see text] = 5) and 30% lesser than the Qchiller at low concentration and low heat capacity ratio ( Cs = 0.25 and [Formula: see text] = 2.5). Solution heat addition rate ( Qadd) per kW cooling capacity ( Qcc) at this solution condition is found as 0.85 kW.

Thermal properties study and performance investigation of potassium formate solution in a falling film dehumidifier/regenerator

Compared with the extensive attention drawn by salt solutions, the promising potassium formate (KCOOH) solution which has smaller causticity and lower price receives little attention in the field of liquid desiccant cooling system (LDCS). Consequently, the present paper studied both the thermal properties and mass transfer performance of KCOOH solution for its practical engineering application. The vapor pressure and density of KCOOH solution under different concentrations and temperatures were measured and then fitted in the form of polynomials with the mean absolute relative deviation (MARD) of 0.06% and 0.551% respectively. Referring to the data in the existing literature, the heat capacity of KCOOH solution was also fitted with the MARD of 0.15%. Mathematical models of dehumidification/regeneration with the film shrinkage on the plate dehumidifier/regenerator were developed and validated by the experimental data. Results showed that the wetting ratio predicted by the model matched well with the measured one with the relative difference of 3.4%. Besides, the dehumidification/regeneration performance obtained by the model in terms of absolute moisture change was also in line with the experimental ones with the MARD of 6.05%/4.2%. In summary, the correlations of KCOOH solution thermal properties, mathematical model, and experimental results were valuable for the engineering application of KCOOH solution in LDCS.

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.

Enthalpies and heat capacities of solution of urea and tetramethylurea in water, ethylene glycol and formamide

Enthalpies of solution of urea (U) and tetramethylurea (TMU) in formamide (FA) and ethylene glycol (Eg) have been experimentally determined from (288 to 328) K. Standard enthalpies and heat capacities of solution of non-electrolytes have been computed and compared with those for aqueous solutions. Heat capacities of solution of U and TMU are rather small and positive for both non-aqueous solvents, whereas in cold water the ΔCp0 values for U and TMU reveal different signs. Our comparative analysis indicates that the behavior of both hydrophilic and hydrophobic species in water differs from that in the non-aqueous solvents with the three dimensional H-bond network, according to our experimental results formamide being a more “water-like” solvent than ethylene glycol.

Enthalpies and heat capacities of solution of methylpheophorbide, dioxidine and their conjugate in DMF at 298-318 K

This paper focuses on the results of the first accurate determination of enthalpies of solution of 9-ethenyl-14-ethyl-21-(methoxycarbonyl)-3-{(O-methylcarbamoyl)ethyl} -4,8,13,18-tetramethyl-20-oxo-phorbine (Methylpheophorbide а, 1), [3-(hydroxymethyl)-1-oxido-4-oxoquinoxalin-4-ium-2-yl]methanol (Dioxidine, 2) and their conjugate 9-ethenyl-14-ethyl-3-{[2-(3-hydroxymethyl)]-1-oxido-4-oxoquinoxalin-4-ium-2-methyleneoxy}carbamoyl}ethyl)-4,8,13,18-tetramethyl-20-oxo-phorbine (Conjugate 3) in liquid N,N-dimethylformamide (DMF) in the temperature range of 298-318 K. Standard enthalpies and heat capacities of solution (ΔC°p) have been computed and compared with those for other solid and liquid non-electrolytes to highlight important features of solvation of potential photosensitizers in a simple model of a protein-like environment.

Determination of mutual solubility between n-alkanes/n-alkylbenzenes and water by using Peng-Robinson equation of state with modified alpha functions and generalized BIP correlations

It is too specific to a given pair (i.e., solubility data must be re-tuned for a new pair, while it is difficult to achieve generalization) for the widely used models, e.g., Henry's law, cubic-plus-association equation of state (CPA EOS), statistical associating fluid theory (SAFT), and specific solubility equations, to predict mutual solubility for hydrocarbon-water pairs, while other constraints such as increased computational expenses and requirement of molecular structures limit their extensive applications. In this study, a generalized methodology has been developed to predict the mutual solubility for n-alkanes (i.e., C3-C20)/n-alkylbenzenes (i.e., C6-C12)-water pairs by using the Peng-Robinson equation of state (PR EOS). A comprehensive database has firstly been developed with the experimentally measured solubility data in a temperature range of 273.2–479.5 K. In addition to the two newly modified alpha functions respectively for hydrocarbons and water, the binary interaction parameters (BIPs) for both aqueous phase and liquid hydrocarbon phase are tuned to match the experimental solubilities. The tuned BIPs are then regressed as functions of reduced temperatures and carbon numbers of hydrocarbons for both aqueous phase and liquid hydrocarbon phase, respectively. The BIP correlations developed in this work can be used to accurately reproduce the experimental measurements with significant improvements over the existing models except for propane-water pair and n-butane-water pair. Also, such newly developed models have been further validated with the experimentally measured heat of solution, solubility minimum temperature, and heat capacity of solution, while sensitivity analysis has been performed to examine the effects of different parameters on the predicted mutual solubility.

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.