Excess Molar Heat Capacities Research Articles

Heat capacities and thermodynamic properties of urea phosphate and its aqueous solutions at various temperatures

Urea phosphate was produced through a complexation reaction of phosphoric acid and urea and subsequent cooling crystallization. The elemental composition analysis, XRD, and FTIR all confirmed that the prepared urea phosphate had high purity and good crystallinity, and showed a clear onset melting temperature of 118.12℃ and corresponding enthalpy change of 222.10 J∙g−1 in TG/DSC measurement. Meanwhile, the heat capacities of urea phosphate and its aqueous solution were carefully measured using microcalorimetry with an expanded relative uncertainty better than 2 %. The experimental results revealed that the heat capacity of urea phosphate rises rapidly with temperature, with an increase of 41 % from −20 to 100℃. The experimental heat capacity data were correlated with semi-empirical models of Maier-Kelley equation, Khodakovsky equation and Debye-Einstein equation which all give excellent reproduction of the measured data with very close average deviation around 0.5 %. The enthalpy, entropy, and Gibbs free energy of solid urea phosphate were estimated at various temperatures by integrating heat capacity against temperature with Maier-Kelley equation and the results confirmed urea phosphate is thermally quite stable below 100℃. The heat capacity of urea phosphate aqueous solution increases with concentration and temperature, and there is a strong linear relationship between the solution’s heat capacity and temperature when the composition remains constant. The apparent molar heat capacity of urea phosphate in solution is positive and increases with concentration and temperature. The extrapolated partial molal heat capacity of urea phosphate is temperature independent and shows an average value of −709.4 J·K−1·mol−1. Due to the partial dissociation and partial ionization of urea phosphate in solution, the excess molar heat capacities show positive deviation from that of ideal solution, which also increases with the increase of concentration and temperature.

Some features of heat capacity changes in aqueous solutions of low molecular weight alkanols at T = 298.15 K and ambient pressure

The specific (cp) and molar (Cp) heat capacities of dilute aqueous solutions of methanol (MeOH), ethanol (EtOH), 1-propanol (n-PrOH) and 2-propanol (i-PrOH) were measured using an adiabatic calorimetry at T = 298.15 K and ambient pressure. Based on the obtained results, the excess molar heat capacities, CpE, as well as the apparent molar heat capacities of each of components, Cp,∅,12, of the system {water (1) + alkanol (2)} were calculated. The standard (at infinite dilution) Cp,2o values were also estimated. All the CpE values are positive and pass through maxima, which shift to the range of a lower mole fraction of alcohol, x2, when the molecular weight of the latter increases. The same goes for the Cp,∅,1max values, too. In turn, the order of changing Cp,∅,2max within the narrow high-diluted range of (∼0.01 <x2 < 0.035) m.f. is oppositely directed. It is established that the x2 value at dCpE/dx2 = 0 is approximately half of the sum of the x2 values at Cp,∅,1max and Cp,∅,2max, a fact indicating the parity contribution of both interacting components of the solution to the structure-energy transformations occurring in it.

Analysis of excess molar heat capacities of three component mixtures comprising of cyclic organic solvents: Graph and Flory theories

The present work reports measurement and estimation of heat capacities, CP and excess heat capacities, (CPE)ijk (using CP data) of 1-methylpiperidine (i) + pyrrolidin-2-one (j) + cycloheptanone or cyclohexanone or cyclopentanone (k) mixtures at several temperatures. (CPE)ijk data have been correlated with the mole fraction of the constitutional molecule (via Redlich-Kister polynomial) to commute standard deviations and ternary coefficients. (CPE)ijkdata have also been examined in terms of Graph and Flory's theories. It has been perceived that (CPE)ijkvalues computed using Graph theory compare well with their corresponding experimental values. Further, (CPE)ijk data obtained by Flory's theory for 1-methylpiperidine (i) + pyrrolidin-2-one (j) + cyclopentanone (k) mixtures are of the same sign.

Viscosity, heat capacity and refractive index studies for binary liquid mixtures containing 1,3-diaminopropane and alkyl acetates: Experimental and theoretical interpretation

The viscosity (η), heat capacity (CP) and refractive index (nD) of 1,3-DAP (1,3-Diaminopropane) (1) + AAc (MAc(methyl acetate), EAc(ethyl acetate), PAc(propyl acetate) and BAc(butyl acetate)) (2) binary mixture were measured at standard ambient temperature i.e. 298.15 K under the atmospheric pressure 0.1 MPa. The data of η, CP and nD were further used to determine deviation in viscosity (Δη), excess molar heat capacity (CPE), excess Gibbs free energy of activation (G∗E), and deviation in refractive index (ΔnD). η were analyzed by Bloomfield and Dewan model (BFD). The η values were further correlated by various correlations like Kendall, Bingham, Kendall-Monroe, Arrhenius, Katti-Chaudhari, Tamura-Kurata, Grunberg-Nissan, Frenkel, Hind-McLaughlin-Ubbelohde, Heric, McAllister, Lulian, Krishnan-Laddha and Heric-Brewer. Further various correlations like Heller, Lorentz-Lorenz, Arago-Biot, Newton, Gladstone-Dale, Erying and Weiner were used to correlate nD data. The derived thermo-physical properties were also interpreted in terms of molecular interactions and correlated with Redlich- Kister polynomial equation (R.K.).

On the interpretation of the unusual behavior of aqueous-organic mixtures in concentration regions with intersecting isotherms of heat capacity properties

Based on our own and some literature results, we have carried out a detailed analysis of concentration regions of the aqueous-organic mixture in which the temperature dependences of both excess molar heat capacity, CpE, and apparent molar heat capacity of each component, Cp,ϕ,i, are intersected. It is established that the ∂CpE/∂T and ∂Cp,ϕ,w/∂Tderivatives (W is water) for the {(W + hexamethylphosphoramide (HMPA)} and {(W + tert‑butanol (t-BuOH)} mixtures intersect in a rather narrow concentration interval between (0.30 and 0.35) and (0.35 and 0.40) mole fractions of the organic component, respectively. This fact we have interpreted as evidence that the decisive role in the mutually overlapping heat-capacity contributions to CpEresulting in such a situation plays the abnormal change in the isobaric molar heat capacity of W (Cp,w), which has a minimum at T ≈ 308 K, when the temperature increases.

Molecular interactions in multicomponent liquid mixtures: Excess molar heat capacities

Molar heat capacities, CP for 1-methylpiperidine (1) + pyrrolidin-2-one (2) + pyridine, α-, β-, γ-picoline (3) mixtures have been assessed at 293.15, 298.15, 303.15, 308.15 K temperatures and same have been employed to compute excess molar heat capacities, CPE. The CPE data have been allied with the composition of the component molecules (Redlich–Kister expansion) and ternary adjustable parameters calculated along with standard deviations. CPE have been verified in terms of Graph theory. Obtained results inferred that commuted CPE values compare favorably well with measured data. Agreement between experimental and calculated CPE values suggest that several assumptions made in driving CPE data are valid.

Molar heat capacities and excess molar heat capacities of mixtures containing ionic liquids and cyclic amides

• The C p , ( C p ) 123 have been assessed for binary and ternary mixtures at several temperatures. • C P E , ( C P E ) 123 have been evaluated using assessed data. • C P E , ( C P E ) 123 data have been analyzed in terms of Graph theory. • Graph theory precisely predicts C P E , ( C P E ) 123 data at the studied mole fractions. Current analysis pertains with the measurement of molar heat capacities, ( C P ) 123 for 1-butyl-2,3-dimethylimidazolium tetrafluoroborate [Bdmim][BF 4 ] or 1-ethyl-3-methylimidazolium tetrafluoroborate [Emim][BF 4 ] (1) + 1-methylpyrrolidin-2-one (NMP) (2) + pyrrolidin-2-one (2-PY) (3) ternary and C P for [Bdmim][BF 4 ] (1) + NMP (2) or 2-PY (3) binary mixtures within temperature series 293.15–308.15 K in a gap of 5 K. Excess heat capacities, ( C P E ) 123 , C P E have been determined using measured data. ( C P E ) 123 , C P E are positive at studied compositions for the ternary and binary mixtures, respectively. ( C P E ) 123 , C P E data have been tested in terms of Graph theory. A reasonable agreement has been perceived between experimental and calculated ( C P E ) 123 , C P E data.

Thermodynamics of mixtures containing amines. XVII. [formula omitted] and [formula omitted] measurements for benzylamine + heptane or + 1-alkanol mixtures at 298.15 K. Application of the DISQUAC and ERAS models

Excess molar enthalpies, HmE, at 298.15 K and 0.1 MPa have been measured by means of a Tian-Calvet microcalorimeter for the systems benzylamine (phenylmethanamine) + heptane, or + methanol, or + 1-propanol, or + 1-pentanol, or + 1-heptanol, or + 1-decanol. In addition, excess molar volumes, VmE, at the same conditions have been also determined using a densimeter Anton Paar model DSA 5000 for the benzylamine + heptane mixture. The HmE of this solution is large and positive since at 298.15 K the system temperature is close to its upper critical solution temperature. Thus, systems with n-alkanes show positive deviations from the Raoult's law. The measured |VmE| values are low, indicating the existence of large structural effects. HmE values of mixtures involving 1-alkanols are large and negative. That is, interactions between unlike molecules are dominant and the systems are characterized by negative deviations from Raoult's law. It is shown that the enthalpy of the hydrogen bonding between molecules of 1-alkanol and benzyalmine are more negative than those between 1-alkanol molecules. The VmE values of the systems with 1-alkanols are also large and negative, and are determined mainly by interactional effects since they increase in line with HmE and with the alcohol size. The different contributions to HmE have been evaluated. The systems have been studied using the DISQUAC and ERAS models. ERAS describes correctly the VmE function. DISQUAC largely improves ERAS results on HmE or on excess molar heat capacities at constant pressure for the mixtures with 1-alkanols, which underlines that physical interactions are very relevant in such solutions.

Coupled structural-thermodynamic modelling of the molten salt system NaCl-UCl3

Molten chloride salts are ionic liquids in which the anions and cations exhibit network formation. An attractive salt system for use in molten salt reactors is NaCl-UCl3, an ionic liquid with complex non-ideal thermodynamic behaviour due to the formation of short-range order. The relationship between local structure and thermodynamic properties is investigated in this work, in which molecular dynamics simulations using the Polarizable Ion Model (PIM) and thermodynamic modelling by means of the CALPHAD method are combined. The system is simulated for a wide range of temperatures and compositions and various properties are derived derived from molecular dynamics data: density/molar volume, thermal expansion, heat capacity and excess properties including excess molar volume, mixing enthalpy and excess heat capacity. Generally, there is good agreement with previously published experimental data. An in depth analysis of the local structure of the liquid is performed for multiple temperatures. This analysis demonstrates the transition from a molecular liquid consisting of primarily Na+, Cl−, UCl63-/UCl74- at low UCl3 content to a polymeric liquid at high UCl3 content, manifesting itself in the formation of species like U2Cl126-, U3Cl178-, U4Cl2210- etc. Exceeding 40% UCl3, the liquid consists of a three-dimensional network of corner or edge-sharing uranium polyhedra. The output of the MD simulations and experimental data are incorporated into a coupled structural-thermodynamic model for the NaCl-UCl3 system based on the quasi-chemical formalism in the quadruplet approximation, that provides a physical description of the melt and reproduces (in addition to the thermodynamic data) the chemical speciation of uranium polymeric species predicted from the simulations.

New insights and coupled modelling of the structural and thermodynamic properties of the LiF-UF4 system

LiF-UF4 is a key binary system for molten fluoride reactor technology, which has not been scrutinized as thoroughly as the closely related LiF-ThF4 system. The phase diagram equilibria in the system LiF-UF4 are explored in this work with X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The short-range ordering in the molten salt solution is moreover surveyed with Extended X-ray Absorption Fine Structure spectroscopy (EXAFS) and interpreted using a combination of standard fitting of the EXAFS data and Molecular Dynamics (MD) simulations with a Polarizable Ion Model (PIM) potential. The density, excess molar volume, thermal expansion, heat capacity, and enthalpy of mixing are extracted from the MD simulations across a range of temperatures and compositions; the behavior is non-ideal, with reasonably good agreement with the experimental data. Also calculated is the distribution of heteropolyanions in the liquid solution, and modelled using the quasi-chemical formalism in the quadruplet approximation taking into account the existence of the single-shell complexes [UF7]3−, [UF8]4−, and the dimeric species [U2F14]6−. Subjecting the optimization of the excess Gibbs energy parameters of the liquid solution to the constraints of the phase diagram data and local structure of the melt as derived from the EXAFS and coupled MD simulations, a CALPHAD-type assessment is proposed, linking structural and thermodynamic properties, with a rigorous physical description of the melt.

Thermodynamics of (water + hexamethylphosphoramide) mixtures: Heat capacity properties in the temperature range between 283.15 K and 298.15 K at ambient pressure

The specific (cp) and molar (Cp) heat capacities of the mixtures of hexamethylphosphoramide (HMPA, or h) with water (w) have been measured using an adiabatic calorimetry at T = (283.15, 288.15, 293.15, and 298.15) K and ambient pressure. Based on the results obtained, the excess molar heat capacities of the mixtures, CpE, as well as apparent molar heat capacities of each component, Cp,ϕ,i (down to its infinite dilution, Cp,i°), have been calculated. The CpE values are positive up to HMPA mole fractions being xh ≈ 0.9 and the dCpE/dT derivative undergoes a positive-to-negative sign inversion at xh = 0.33. Both concentration and temperature dependences of Cp,ϕ,i have also a complex character. The correlations of molar heat capacity properties with volume-related those for (H2O + HMPA) at the same temperatures have been discussed, too.

Densities, speeds of sound and molar heat capacities of solvent mixtures containing cyclic ethers and piperidine

Abstract For the binary mixtures comprised of piperidine (1) + tetrahydrofuran or 1,3-dioxolane or 1,4-dioxane (2) densities, ρ, speeds of sound, u, and molar heat capacities, C P m were measured at temperatures ranging from (293.15 to 308.15) K with 5 K interval and 0.1 MPa. Based on these measurements, excess molar volumes, V m E , excess isentropic compressibilities, κ S E and excess molar heat capacities, C P m E were determined and the same have been fitted to the Redlich-Kister equations to estimate binary adjustable parameters along with the standard deviations. The V m E , κ S E and C P m E data have been discussed to interpret molecular interactions operating among the constituent molecules and molecular entities have been proposed in pure and mixed state. Quantum mechanical calculations support the existence of these molecular entities.

Isobaric heat capacity of the binary liquid (water + 1,2–propanediol) mixtures at high-temperatures and high-pressures

Isobaric heat capacity, CP, of binary aqueous 1,2 − propanediol solutions have been measured over the temperature range from room temperature 298.15 K to 473.15 K at pressures up to 30 MPa using differential scanning calorimeter (DSC, ITS-400). The measurements were performed for three concentrations of 0.0731, 0.1914, and 0.4153 mol fraction of 1,2 − propanediol. The expanded uncertainty of the heat capacity (CP), pressure (P), temperature (T), and concentration (x) measurements at the 95% confidence level with a coverage factor of k = 2 is estimated to be 2.4%, 0.05%, 15 mK, and 0.0001, respectively. The measuredCPPTx data have been used to calculate excess molar heat capacities (CPmE) of the mixture. The second temperature derivatives of specific volume or curvature of the Vm-T isobars have been calculated using the pressure dependence measured heat capacities along the isotherms as ∂2Vm/∂T2Px=-T-1∂CPm/∂PTx. Some unusual behaviour of CP in the low concentration range (below 0.2 mol fraction, dilute mixture) along the each measured isotherms-isobars was found.

Excess molar heat capacity for the binary system n-propyl alcohol + water in the temperature range 278.15–358.15 K: new data and application for excess enthalpy calculation

In this work, the new set of the data on the excess heat capacity (CPE ), density (ρ) and excess volumes (VE) for binary system n-propanol + water in the temperature range 278.15–358.15 K are presented. The concentration dependence of CPE was correlated using Redlich–Kister equation. Obtained experimental data of CPE were used to calculate excess enthalpies at various temperatures.

An experimental investigation and modelling of the thermal and caloric properties of nanofluids isopropyl alcohol - Al2O3 nanoparticles

An influence of Al2O3 nanoparticles on the thermodynamic properties of isopropyl alcohol in the liquid phase has been studied. Experimental measurements of the two-phase specific heat capacity have been performed in the temperature range from 184 to 340 K for samples with the mass fractions of the nanoparticles 0.0201, 0.0511 and 0.0996 kg·kg-1. The method of monotonic heating in an adiabatic calorimeter of variable temperature has been applied. The saturated vapor pressure of the nanofluids has been measured at the temperatures from 297 to 352 K and concentrations of the nanoparticles in isopropyl alcohol 0.0253, 0.0444, 0.0687, 0.0955 kg·kg-1. The results obtained have shown that the specific isobaric heat capacity of the nanofluids decreases up to 8.6% at 0.0996 kg·kg-1 of Al2O3 nanoparticles in comparison with pure isopropyl alcohol. In addition, the influence of Al2O3 nanoparticles on the specific enthalpy and specific entropy of isopropyl alcohol in the liquid phase has been examined. It is established that both the specific heat capacity of the material of the nanoparticles and structural changes of the base fluid around the nanoparticles are main factors that determine a decrease of the specific isobaric heat capacity of isopropyl alcohol. It was shown that the excess molar volume and excess molar isobaric heat capacity are determined by properties of the interfacial phase of structurally oriented isopropyl alcohol molecules on the surface of nanoparticles. A new three-phase model for prediction the molar isobaric heat capacity of nanofluids is proposed. To predict caloric properties of nanofluids the proposed model requires only data for the molar volume of the investigated samples.

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.

Isobaric molar heat capacities measurement of binary mixtures containing ethyl laurate and ethanol at high pressures

A flow calorimeter was used to determine the isobaric molar heat capacities of mixtures containing ethyl laurate and ethanol at temperatures from 313.15 K to 343.15 K and pressures up to 25 MPa. The experimental system was verified by measuring the isobaric molar heat capacities of pure ethanol at different temperatures and pressures, and the relative expanded uncertainty of the measurement results was estimated to be lower than 1.45%. Then, the excess molar heat capacity which characterizes the deviation of the mixtures from the ideality was evaluated. Moreover, the excess molar heat capacities were analyzed, and a Redlich-Kister type correlation was presented for fitting. After that, absorbing the Redlich-Kister correlation, a new correlation for the isobaric molar heat capacities of mixtures was proposed, and the calculated results were compared with the experimental data. At last, to reduce the parameters used in calculation process, another correlation for the isobaric molar heat capacities of mixtures was also proposed, and a comparison of two correlations was implemented.

Thermophysical and volumetric study of mixtures {p-cymene + propan-1-ol} at several temperatures and atmospheric pressure. Modeling with COSMO-RS

Abstract Experimental isobaric molar heat capacities at atmospheric pressure have been determined for the mixture {p-cymene + propan-1-ol} every 10 K in the temperature interval (298.8–328.5) K and over the entire composition range with a Calvet type calorimeter. Densities, necessary for calculating heat capacities, have been also measured in similar conditions. Excess molar volumes have been calculated from densities. They are positive at (318.15 and 328.15) K and sigmoidal at (298.15 and 308.15) K with negative values in the zone very rich in propan-1-ol. Excess molar heat capacities have been calculated from the molar heat capacities and show positive values. Both excess molar properties increase as the temperature rises at a given molar fraction. Excess properties are discussed in terms of intermolecular interactions. The solvation model COSMO-RS has been applied to predict the excess molar heat capacities, being the quantitative predictions rather poor.

Measurement and prediction of thermodynamic properties of ternary mixtures containing [Bmim][BF4] - [Emim][BF4] – cyclopentanone or cyclohexanone

In this study, excess molar enthalpies, H123E and molar heat capacities, (CP)123 of ternary [Bmim][BF4] (1)+[Emim][BF4] (2)+cyclopentanone or cyclohexanone (3) mixtures (as a potential solvent system for heat transfer processes) have been measured over the entire range of composition. The (CP)123 and H123E measurements have been carried out over temperature range 293.15K to 308.15K with 5K interval and 298.15K respectively. The observed (CP)123 data have been utilized to determine excess heat capacities, (CPE)123. While H123Evalues for investigated mixtures are negative, (CPE)123 are positive over entire mole fraction range of (1) and (2) components. The H123E and (CPE)123 data of the present mixtures have also been tested in terms of Graph theory. It has been observed that H123E and (CPE)123 values calculated by Graph theory are in comparison with the experimental data.

A new insight into pure and water-saturated quaternary phosphonium-based carboxylate ionic liquids: Density, heat capacity, ionic conductivity, thermogravimetric analysis, thermal conductivity and viscosity

Abstract Ionic Liquids (ILs) are task specific materials with tunable properties which may be applied as heat transfer fluids (HTFs) due to their characteristic properties including low vapour pressure, wide liquid range and high thermal stability. This study provides an evaluation of their potential as HTFs from both their physicochemical properties as well as an economic comparison with commonly used materials. The paper presents the thermophysical properties (density, isobaric heat capacity, ionic conductivity, viscosity, thermal stability by TGA, thermal conductivity) and their thermodynamic derivatives (isobaric thermal expansion coefficient, excess molar volume, excess molar heat capacity), as well as the Walden rule of ionicity for a range of hydrophobic ILs based on the trihexyl(tetradecyl)phosphonium, ([P14,6,6,6]+), cation. The ionic liquids studied are trihexyl(tetradecyl)phosphonium acetate ([AcO]−), butanoate ([ButO]−), hexanoate ([HexO]−), octanoate ([OctO]−), and decanoate ([DecO]−), as well as their mixtures with water. It was shown that investigated systems are highly promising materials as HTFs, especially ILs + water mixtures, which may be the solution for many engineering issues.