Heat Capacities Of Aqueous Solutions Research Articles

Експериментално определяне зависимостта на специфичния топлинен капацитет на водни разтвори на LiCl от температурата и концентрацията им

This project is focused on the experimental determination of the specific heat capacity of aqueous solutions of LiCl with different mass concentrations proposed, which is applicable for various liquids and, in contrast to calorimetry, relies on the heat transfer between two media with different temperatures and thus accounts for the heat losses of this thermodynamic system. A theoretical model based on the heat balance equation for Newtonian and Stephan-Boltzmann heat transfer has been constructed. Laboratory experiments have been carried out using aqueous solutions of LiCl with mass concentration ranging from 0 to 15% and at temperatures in the range 20-90 ℃. The data has been analysed using MATLAB and empiric equations for the temperature dependence of the specific heat capacity for fixed mass concentrations of the solute have been obtained. The results are in good agreement with the reference values.

Volumes and Heat Capacities of Cobalt(II), Nickel(II), and Copper(II) Sulfates in Aqueous Solution

The densities and isobaric volumetric heat capacities of aqueous solutions of the sulfate salts of cobalt(II), nickel(II), and copper(II) have been measured at 298.15 K and 0.1 MPa using vibrating-...

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.

Heat Capacities of Aqueous Solutions of K4Fe(CN)6, K3Fe(CN)6, K3Co(CN)6, K2Ni(CN)4, and KAg(CN)2 at 298.15 K

Isobaric volumetric heat capacities of aqueous solutions of K4Fe(CN)6, K3Fe(CN)6, K3Co(CN)6, K2Ni(CN)4, and KAg(CN)2 have been measured at 298.15 K over the approximate concentration range 0.02 to 0.4 mol·kg–1 using a Picker flow calorimeter. These data were combined with measured densities to calculate the corresponding apparent molar isobaric heat capacities, Cpϕ. The values so obtained were fitted as a function of concentration using an extended Redlich–Rosenfeld–Meyer-type equation to provide the standard state (infinite dilution) quantities, Cpϕo, for each salt. The Cpϕ values for all the salts studied showed similar dependences on concentration, with a slight upward curvature at higher molalities, possibly due to anion aggregation. Values of Cpϕo for the aquated cyanometallate anions were estimated using the tetraphenylphosphonium tetraphenylborate extrathermodynamic assumption and were little affected by ion size but were strongly dependent on ionic charge, ranging from −191 J·K–1·mol–1 for [Fe(CN)...

Molar Volumes and Heat Capacities of Aqueous Solutions of Potassium Hydroxide and for Water Ionization up to 573 K at 10 MPa

Densities (ρ) and isobaric volumetric heat capacities (σp) of carefully purified aqueous solutions of potassium hydroxide have been measured at concentrations up to 6 mol·kg–1 at a pressure of 10 MPa over the temperature range 323 ≤ T/K ≤ 573 using a vibrating-tube densimeter and a Tian–Calvet differential calorimeter, respectively. Apparent molar volumes (Vϕ) and isobaric heat capacities (Cpϕ) calculated from these data were fitted with modified Redlich–Meyer type equations to derive the corresponding standard molar volumes and heat capacities at infinite dilution. Exact comparisons with literature data were not possible because of pressure differences but the present values, which greatly extend the database for KOH(aq) in terms of precision, temperature and concentration, are broadly compatible with most of the earlier results. Comparison of the present values of Vϕ and Cpϕ for KOH(aq) with corresponding data for solutions of the other alkali metal hydroxides indicated that all of these systems show si...

Heat Capacities of Aqueous Solutions of Lithium Sulfate, Lithium Perchlorate, and Lithium Trifluoromethanesulfonate at 298.15 K

Isobaric heat capacities of aqueous solutions of Li2SO4, LiClO4, and LiCF3SO3 have been measured at 298.15 K and 0.1 MPa up to high concentrations using a Picker flow calorimeter. Apparent molar isobaric heat capacities, Cp,ϕ, derived from these data were fitted within the limits of experimental precision with an extended Redlich–Rosenfeld–Meyer type of equation, which was also used to estimate the standard state (infinite dilution) quantities, Cp,ϕo, for each salt. The latter values were combined with appropriate literature data to produce a robust estimate of Cp,ϕo (Li+(aq)) = −3 ± 2 J·K–1·mol–1. Where comparison was possible, Cp,ϕ(LinX) values were closely parallel to those of the corresponding acids over the whole concentration range, even when the shapes of the curves were highly unusual. In contrast, Cp,ϕ(NanX) values always exhibited a crossover with the lithium salt data at a concentration of about 1 mol·kg–1, which appears to reflect differences in the hydration of the two cations.

ISOCHORIC HEAT CAPACITY OF 1% AQUEOUS SOLUTION OF MAGNESIUM CHLORIDE

Aim . The aim is to conduct an experimental study of isochoric heat capacity of 1% aqueous solution of magnesium chloride along the phase boundary curve. Method. In order to determine the isochoric heat capacity at the phase boundary curve we used the adiabatic calorimeter of KH. I. Amirkhanov. Results . Results of the study of the isochoric heat capacity depending on the temperature are given in tables and figures; the findings are compared with those of other researchers. When evaluating a complex system, we ought not to evaluate its effectiveness on the basis of only one criterion, even a very important, in this case must take into account the requirements of the technical, economic, environmental and of other natures. Conclusions . When solving optimization problems of efficiency in geothermal energy it is necessary to take into account the fact of the temperature dependence of the heat and density. The temperature dependence of the density and heat capacity in the calculations significantly affect the value of the efficiency criterion to be taken into account, otherwise the calculation error can be up to 20%. The data obtained from the isochoric heat capacity of aqueous solutions of magnesium chloride is compared with the data for water and aqueous solutions of NaCl and NaOH, obtained previously, which may be represented as a model of geothermal and sea water.

Molar heat capacity of aqueous solutions of 1,3-diaminopropane and 1,4-diaminobutane and their piperazine blends

The molar heat capacity, Cp, of aqueous 1,3-diaminopropane (DAP), 1,4-diaminobutane (DAB) and their corresponding blends with piperazine (PZ) were measured at temperatures from 303.2K to 353.2K by differential scanning calorimetry. The correlation of Cp of the aqueous binary mixtures with temperature and concentration was successfully described by a Redlich–Kister type equation using excess molar heat capacity data. A modified Sohnel and Novotny equation was used to represent the temperature and concentration dependence of Cp of the ternary mixtures. The average absolute deviations between the experimental and the predicted Cp data were 0.2% and 0.1% for the binary and ternary mixtures, respectively. The results suggest that the experimental data presented in this work were represented well by the proposed correlations.

A Semi-Empirical Model for Estimating the Heat Capacity of Aqueous Solutions of Alkanolamines for CO2 Capture

A semiempirical model for estimating the heat capacity of aqueous solutions of alkanolamines, both before and after CO2 absorption, has been developed, and the model parameters for several systems have been obtained using regression techniques. Furthermore, the heat capacity data for pure monoethanolamine (MEA), diethanolamine (DEA), N-methyldiethanolamine (MDEA), 2-amino-2-methyl-1-propanol (AMP), and piperazine (PZ), as well as the heat capacity data for aqueous solutions of the alkanolamines that have been reported in the open literature, have been analyzed. Given that the data reported by the several different authors for the same system were not weighted during the regression, key statistics of the model predictions against the experimental data set used in the model fitting have been used in the assessment of the relative accuracy of the experimental data reported by different authors for the same system. Overall, the model predictions are in excellent agreement with most of the experimental data th...

Hydrogen Ion (H+) in Waste Acid as a Driver for Environmentally Sustainable Processes: Opportunities and Challenges

Acid-base neutralization reaction in the aqueous phase is thermodynamically favorable and kinetically fast. Waste acid neutralization is also the most common waste management practice globally. However, waste acid neutralization is yet to be used for any work/energy generation because of the low concentrations of the waste acid and the high heat capacity of aqueous solutions. In this paper, we address potential processes that can effectively take advantage of the high energy inherent in neutralization reactions, in accordance with the goal of sustainable development.

Standard molar volumes and heat capacities of aqueous solutions of sodium trifluoromethanesulfonate at temperatures up to 573 K and pressures to 28 MPa

Densities and heat capacities of aqueous solutions of sodium trifluoromethanesulfonate (sodium triflate) of concentrations from 0.025 to 0.3mol·kg−1 were measured with high temperature, high pressure custom-made instruments at temperatures up to 573K and at pressures up to 28MPa. Standard molar volumes and standard molar heat capacities were obtained via extrapolation of the apparent molar properties to infinite dilution. The results for volumetric properties are consistent with earlier literature data, but no previous measurements exist for heat capacities of sodium triflate at superambient conditions. The new data were used for calculating the standard molar volumes and heat capacities for the triflate anion and compared with the results for triflic acid that should be essentially identical within the expected error margins. At temperatures above 473K an effort was made to refine the processing of literature data for HCl(aq), taking into account its partial association, and subsequently to modify the value for Na+ ion calculated from the standard thermodynamic values of NaCl(aq) where its ion pairing was already considered. This approach yields reasonable agreement at high temperatures between the values for triflate ion calculated from its salt and those for triflic acid.

Heat capacity and phase behavior of aqueous diethylene glycol n-pentyl ether by DSC

The specific heat capacities of aqueous solutions of diethylene glycol n-pentyl ether (C5E2) with molalities m2≤1.8232molkg−1 were measured within the temperature range 273.15–338.15K by DSC. Changes in the specific, apparent and partial molar heat capacities of the aqueous system investigated were analyzed and considered as an effect of structural transformations in order to determine the boundary between the region, within which the molecules of amphiphile occur in the form of monomers, and the area, in which the first large aggregates or micelles appear. For each solution, the temperature dependence of differential heat flow was analyzed in order to determine the temperature of phase transition and the boundary between mono- and diphase systems.

Molar Volumes and Heat Capacities of Aqueous Solutions of Short-Chain Aliphatic Sodium Carboxylates at 25 °C

Densities and isobaric heat capacities of the aqueous solutions of the sodium salts of the four smallest straight-chain aliphatic carboxylates: sodium methanoate (formate), ethanoate (acetate) n-propanoate, and n-butanoate have been measured at 25 degrees C and 0.1 MPa by vibrating-tube densimetry and Picker flow calorimetry, respectively. All systems were investigated at concentrations ranging from approximately 0.02 mol.kg(-1) near saturation, which extends the existing database to higher concentrations for all of these salts. Apparent molar isobaric heat capacities and volumes derived from the data were fitted with an extended Redlich-Meyer equation to determine the standard state partial molar quantities. At concentrations where comparisons were possible, the present results generally agreed well with previous determinations. An exception was the heat capacities of sodium formate solutions, where the present results at low solute concentrations appear to be influenced by an unidentified thermal effect. The apparent molar quantities, especially the heat capacities, provide indirect evidence of aggregation by the longer-chain aliphatic carboxylates at high concentrations.

Adiabatic compressibility and structural features of non-electrolyte aqueous solutions

Structural characteristics of the hydration complexes of non-electrolytes such as the hydration numbers h, molar adiabatic compressibility of hydration complexes βhVh, the molar volume of water in the hydration sphere V1h, the solute molar volume without hydration environments V2h and others are determined using the data on the ultrasonic velocity, the density and heat capacity of aqueous solutions of urea, urotropine, acetonitrile, and a number of amides of N-acetyl amino acids. A theoretical model of solvation is also applied. A comparison of the environments of hydrated urotropine molecules with those of urea and acetonitrile molecules in an aqueous medium shows a considerable hydrophobic interaction of urotropine with a solvent.

Heat Capacity of Sodium Aminoacetate Solutions before and after CO2 Absorption

The heat capacities of aqueous solutions of sodium aminoacetate (CAS no. 6000-44-8) and CO2-loaded aqueous sodium aminoacetate solutions were measured for a range of sodium aminoacetate mass fractions w = (0.01, 0.05, 0.10, 0.15, 0.20, and 0.30) and at a temperature range of T = (298.15 to 323.15) K. It was found that the heat capacity of the aqueous solution of sodium aminoacetate decreases as the concentration increases and increases with an increase in temperature. The heat capacity of CO2-loaded aqueous sodium aminoacetate solution was found to increase with temperature and decrease with an increase in CO2 loading. The heat capacities of the CO2-loaded aqueous sodium aminoacetate solution were lower than those of the unloaded solutions.

Heat capacities of aqueous solutions containing diethanolamine and N-methyldiethanolamine

In this work, we present new results for heat capacities of aqueous mixtures of diethanolamine with N-methyldiethanolamine over the temperature range (303.2 to 353.2) K with a differential scanning calorimeter. For mole fractions of water ranging from 0.2 to 0.8, 16 concentrations of the (DEA + MDEA + water) systems were investigated. For the binary system, (DEA + MDEA), heat capacities of nine concentrations were also measured. A Redlich–Kister-type equation for representing excess molar heat capacity was applied to correlate the measured C p of aqueous alkanolamine solutions. For a total of 176 data points for the (DEA + MDEA + water) system, the overall average absolute percentage deviation of the calculations are 16.5% and 0.2% for the excess molar heat capacity and the molar heat capacity, respectively. The heat capacities presented in this study are, in general, of sufficient accuracy for most engineering-design calculations.

A Model for Calculating the Heat Capacity of Aqueous Solutions, with Updated Density and Viscosity Data

A model for calculating the heat capacity of complex aqueous solutions with an arbitrary number of solutes and at an arbitrary temperature was developed. Parameters for 79 solutes were established based on a critical review of the literature for solutions of one solute in water, with about 6600 points included. The average difference between the calculated and experimental heat capacity is −0.0003 kJ·kg−1·K−1 with a standard deviation of 0.010 kJ·kg−1·K−1. The model was validated by comparing published and calculated heat capacities for 13 systems of more than one solute in water, with a total of 485 data points. The average difference between experimental and calculated values is −0.003 kJ·kg−1·K−1 with a standard deviation of 0.029 kJ·kg−1·K−1. Data are presented on the following 109 solutes, including data on density (16 300 points) and viscosity (10 700 points): (NH4)2SO4, Al2(SO4)3, AlCl3, Ba(NO3)2, BaCl2, Ca(CH3CO2)2, Ca(NO3)2, CaCl2, CaSO4, Cd(NO3)2, CdCl2, CdSO4, CH3CH2OH, CO2, CoCl2, CoSO4, Cr2(SO4)3, CrCl3, Cu(NO3)2, CuCl2, CuSO4, Fe2(SO4)3, FeCl2, FeCl3, FeSO4, H2O2, H2SO4, H3AsO3, H3AsO4, H3PO4, HBr, HCH3CO2, HCHO2, HCl, HCN, HNO3, K2CO3, K2Cr2O7, K2HPO4, K2SO4, K3PO4, KBr, KCH3CO2, KCHO2, KCl, KF, KH2PO4, KHCO3, KHSO3, KI, KNO2, KNO3, KOH, Li2SO4, LiCH3CO2, LiCl, LiNO3, LiOH, Mg(CH3CO2)2, Mg(NO3)2, MgCl2, MgSO4, Mn(NO3)2, MnCl2, MnSO4, Na2C2O4, Na2CO3, Na2CrO4, Na2HPO4, Na2MoO4, Na2S, Na2S2O3, Na2SO3, Na2SO4, Na2WO4, Na3PO4, NaAl(OH)4, NaBr, NaCH3CO2, NaCHO2, NaCl, NaClO3, NaF, NaH2PO4, NaHCO3, NaHS, NaHSO3, NaHSO4, NaI, NaMnO4, NaNO2, NaNO3, NaOH, NH3, NH4Cl, NH4HCO3, NH4NO3, Ni(NO3)2, NiCl2, NiSO4, Pb(NO3)2, SO2, Sr(NO3)2, SrCl2, Sucrose, TiOSO4, Zn(NO3)2, ZnCl2, ZnSO4.

Standard Molar Volumes and Heat Capacities of Aqueous Solutions of Trifluoromethanesulfonic Acid at Temperatures up to 573 K and Pressures to 30 MPa

Densities and heat capacities of dilute aqueous solutions (0.025 to 0.4 mol⋅kg−1) of trifluoromethanesulfonic acid (triflic acid) were measured with original high-temperature, high-pressure instruments at temperatures and pressures up to 574 K and 31 MPa, respectively. Standard molar volumes and standard molar heat capacities were obtained via extrapolation of the apparent molar properties to infinite dilution. The evolution of these standard derivative properties of triflic acid with temperature and pressure is qualitatively compared with that of other acids of different strengths.

Heat capacities of aqueous solutions of sodium hydroxide and water ionization up to 300 °C at 10 MPa

A commercial (Setaram C80) calorimeter has been modified to measure the heat capacities of highly caustic solutions at temperatures up to 300 °C and pressures up to 20 MPa. The improvements have allowed more accurate determination of the isobaric volumetric heat capacities of chemically aggressive liquids at high temperatures. Test measurements with aqueous solutions of sodium chloride showed a reproducibility of about ±0.1%, with an accuracy of ∼0.3% or better, over the whole temperature range. Heat capacities of aqueous solutions of sodium hydroxide at concentrations from 0.5 to 8 mol/kg were measured at temperatures from 50 to 300 °C and a pressure of 10 MPa. Apparent molar isobaric heat capacities of NaOH(aq) were calculated using densities determined previously for the same solutions by vibrating-tube densimetry. Standard state (infinite dilution) partial molar isobaric heat capacities of NaOH(aq) were obtained by extrapolation using an extended Redlich–Meyer equation. Values of the standard heat capacity change for the ionization of water up to 300 °C were derived by combining the present results with the literature data for HCl(aq) and NaCl(aq).

Liquid Heat Capacity of Aqueous Solutions Containing Diethanolamine and 2-Piperidineethanol

Liquid heat capacities of aqueous mixtures of diethanolamine (DEA) with 2-piperidineethanol (2-PE) were measured over the temperature range of 303.2 to 353.2 K with a differential scanning calorimeter. For mole fractions of water ranging from 0.2 to 0.8, 16 concentrations of the DEA + 2-PE + water systems were studied. For binary systems, heat capacities of the nine concentrations of DEA + 2-PE were also studied. A Redlich–Kister-type equation for representing excess molar heat capacity was applied to correlate the measured Cp of aqueous alkanolamine solutions. For a total of 176 data points for the DEA + 2-PE + water system, the overall average absolute percent deviation of the calculations were 10.6% and 0.1% for the excess molar heat capacity and the molar heat capacity, respectively. The heat capacities of aqueous mixtures of DEA with 2-PE presented in this study are, in general, of sufficient accuracy for most engineering-design calculations.