Isobaric Molar Heat Capacities Research Articles

Liquid densities, heat capacities, refractive index and excess quantities for {protic ionic liquids + water} binary system

Densities, ρ, of aqueous solutions of the room temperature protic ionic liquid (PIL), pyrrolidinium nitrate are determined at the atmospheric pressure over the temperature range from (283.15 to 323.15) K and within the whole composition range. The molar isobaric heat capacities, C p , and refractive index, n D, of {PIL + water} binary system are measured at 298.15 K. The excess molar volumes V E, excess molar isobaric heat capacities C p E , and deviation from ideality of refractive index Δ ϕn , of pyrrolidinium nitrate aqueous solutions were deduced from the experimental results as well as apparent molar volumes V ϕ , partial molar volumes V ¯ m, i , and thermal expansion coefficients α p . The V E values were found to be positive over the entire composition range at all temperatures studied therein, whereas deviations from ideality were negative for refractive index Δ ϕn . The volumetric properties of binary mixtures containing water and four other protic ionic liquids, such as pyrrolidinium hydrogen sulfate, pyrrolidinium formate, collidinium formate, and diisopropyl-ethylammonium formate were also determined at 298.15 K. Results have been then discussed in terms of molecular interactions and molecular structures in these binary mixtures.

Gas Nonideality at One Atmosphere Revealed Through Speed of Sound Measurements and Heat Capacity Determinations

Using an easy-to-make cylindrical resonator, students can measure the speed of sound in a gas, u, with sufficiently high precision (by locating standing-wave Lissajous patterns on an oscilloscope) to observe real gas properties at one atmosphere and 300 K. For CO2 and SF6, u is found to be 268.83 and 135.25 m s–1, respectively, versus their ideal-gas (zero-pressure) values of 270.15 and 136.67 m s–1. These differences arise from intermolecular interactions. It is shown that if the molar isobaric heat capacities, Cp, m, are calculated from the one atmosphere u values assuming perfect gas behavior, significant errors are produced. For CO2 and SF6 these errors are 2.7% and 25%, respectively. Experimental Cp, m values are compared with those obtained based on the equipartition theorem.

Isobaric thermal expansivity of the binary system 1-hexanol + n-hexane as a function of temperature and pressure

The isobaric thermal expansivity against temperature and pressure for the system 1-hexanol + n-hexane was directly determined by means of a calorimetric method. From these data, the excess isobaric thermal expansivity is calculated at representative temperatures and pressures. The obtained results for this excess quantity are qualitatively discussed by applying well-known arguments often used for explaining the thermodynamic behavior of alcohol + alkane mixtures. In order to check the consistency of these data with those of literature, the derivative of excess molar volume against temperature and that of excess isobaric molar heat capacity against pressure are calculated and compared with those obtained from literature data. Very good coherence between both data sources is obtained.

Excess enthalpy, density, and heat capacity for binary systems of alkylimidazolium-based ionic liquids + water

Experimental measurements of excess molar enthalpy, density, and isobaric molar heat capacity are presented for a set of binary systems ionic liquid + water as a function of temperature at atmospheric pressure. The studied ionic liquids are 1-butyl-3-methylpyridinium tetrafluoroborate, 1-ethyl-3-methylimidazolium ethylsulfate, 1-butyl-3-methylimidazolium methylsulfate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate. Excess molar enthalpy was measured at 303.15 K whereas density and heat capacity were determined within the temperature range (293.15 to 318.15) K. From experimental data, excess molar volume and excess molar isobaric heat capacity were calculated. The analysis of the excess properties reveals important differences between the studied ionic liquids which can be ascribed to their capability to form hydrogen bonds with water molecules.

Excess molar properties for binary systems of alkylimidazolium-based ionic liquids + nitromethane. Experimental results and ERAS-model calculations

Density, isobaric molar heat capacity, and excess molar enthalpy were experimentally determined at atmospheric pressure for a set of binary systems ionic liquid + nitromethane. The studied ionic liquids were: 1-butyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylpyridinium tetrafluoroborate, 1-ethyl-3-methylimidazolium ethylsulfate, 1-butyl-3-methylimidazolium methylsulfate, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, and 1-butyl-3-methylimidazolium trifluoromethanesulfonate. Density and heat capacity were obtained within the temperature range (293.15 to 318.15) K whereas excess molar enthalpy was measured at 303.15 K; excess molar volume and excess molar isobaric heat capacity were calculated from experimental data. The ERAS-model was applied in order to study the microscopic mechanisms involved in the mixing process. Although the studied compounds are not self-associated, ERAS-model describe adequately the experimental results if cross-association between both compounds is considered.

Excess properties for binary systems ionic liquid + ethanol: Experimental results and theoretical description using the ERAS model

Density, isobaric molar heat capacity and excess molar enthalpy were experimentally determined at atmospheric pressure for a set of binary systems of ionic liquids and ethanol. Density and heat capacity were obtained within the temperature range (293.15–318.15 K) whereas excess molar enthalpy was measured at 303.15 K; excess molar volume and excess molar isobaric heat capacity were calculated from experimental data. The Extended Real Associated Solution (ERAS) model is applied to extract information about the association capability of each ionic liquid with ethanol molecules through hydrogen bonds. The chemical nature of the anion is revealed as the main factor that determines the thermodynamic behavior of the studied systems.

Noncontact modulated laser calorimetry of liquid silicon in a static magnetic field

Accurate thermal transport properties of high-temperature liquid silicon, such as those of heat capacity, emissivity, and thermal conductivity, are required for improving numerical modeling to produce high-quality silicon crystals using the Czochralski method. However, contamination from contact material and convection complicates measurements of these properties. The authors developed a noncontact modulated laser calorimetry using electromagnetic levitation in a static magnetic field. The isobaric molar heat capacity, thermal conductivity, and hemispherical total emissivity of liquid silicon were measured simultaneously at temperatures of 1750–2050 K. Convection in the levitated liquid silicon was suppressed above a static magnetic field of 2 T.

Thermophysical Properties of N-Octyl-3-methylpyridinium Tetrafluoroborate

Density, speed of sound, refractive index, surface tension, isobaric molar heat capacity, and kinematic viscosity of the room-temperature ionic liquid N-octyl-3-methylpyridinium tetrafluoroborate have been measured over a temperature range. From the results, coefficients of thermal expansion, molar refractions, and dynamic viscosities have been derived. The properties are discussed further in terms of the effect of the variations of the alkyl chain length on the pyridinium cation.

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).

Thermophysic Comparative Study of Two Isomeric Pyridinium-Based Ionic Liquids

A comprehensive thermophysical study of isomeric room-temperature ionic liquids n-butyl-3-methyl-pyridinium tetrafluoroborate and n-butyl-4-methyl-pyridinium tetrafluoroborate has been performed. This paper reports various experimental data including density, speed of sound, refractive index, surface tension, isobaric molar heat capacity, and kinematic viscosity. From the experimental results, coefficients of thermal expansion, dynamic viscosities and molar refractions of the studied ionic liquids have been determined. Results have been analyzed paying special attention to the different features of the isomers and their structural differences. Several theories and empirical relations have been applied in order to predict physical properties of ionic liquids. A good agreement between experimental and calculated data has been found. Furthermore, a study about the versatility and application of the different relationships has been carried out finding that in general density and coefficients of thermal expansion can be estimated with relatively good accuracy.

Vapor Pressure, Speed of Sound, and PVT-Properties of R-404a in the Vapor Phase

The density (300–363 K, up to 3.5 MPa) and speed of sound (293–373 K, 7.5–480 kPa) in gaseous R-404a have been studied by an isochoric piezometer method and an ultrasonic interferometer, respectively. The pressures of the saturated vapor along the dew line were measured from 298 to 330 K. The experimental uncertainties of the temperature, pressure, density, and speed-of-sound measurements were estimated to be within ±20 mK, ±1.5 kPa, ±0.15%, and ±(0.1–0.2)%, respectively. On the basis of the obtained data, the isobaric molar heat capacity of R-404a was calculated for the ideal-gas state. An eight-coefficient Benedict–Webb–Rubin equation of state has been developed for the gaseous phase of R-404a.

Isentropic expansion and related thermodynamic properties of non-ionic amphiphile–water mixtures

A concise thermodynamic formalism is developed for the molar isentropic thermal expansion, ES,m = ( partial differential Vm/ partial differential T)(Sm,x), and the ideal and excess quantities for the molar, apparent molar and partial molar isentropic expansions of binary liquid mixtures. Ultrasound speeds were determined by means of the pulse-echo-overlap method in aqueous mixtures of 2-methylpropan-2-ol at 298.15 K over the entire composition range. These data complement selected extensive literature data on density, isobaric heat capacity and ultrasound speed for 9 amphiphile (methanol, ethanol, propan-1-ol, propan-2-ol, 2-methylpropan-2-ol, ethane-1,2-diol, 2-methoxyethanol, 2-ethoxyethanol or 2-butoxyethanol)-water binary systems, which form the basis of tables listing molar and excess molar isobaric expansions and heat capacities, and molar and excess molar isentropic compressions and expansions at 298.15 K and at 65 fixed mole fractions spanning the entire composition range and fine-grained in the water-rich region. The dependence on composition of these 9 systems is graphically depicted for the excess molar isobaric and isentropic expansions and for the excess partial molar isobaric and isentropic expansions of the amphiphile. The analysis shows that isentropic thermal expansion properties give a much stronger response to amphiphile-water molecular interactions than do their isobaric counterparts. Depending on the pair property-system, the maximum excess molar isentropic value is generally twenty- to a hundred-fold greater than the corresponding maximum isobaric value, and occurs at a lower mole fraction of the amphiphile. Values at infinite dilution of the 9 amphiphiles in water are given for the excess partial molar isobaric heat capacity, isentropic compression, isobaric expansion and isentropic expansion. These values are interpreted in terms of the changes occurring when amphiphile molecules cluster into an oligomeric form. Present results are discussed from theoretical and experimental thermodynamic viewpoints. It is concluded that isentropic thermal expansion properties constitute a new distinct resource for revealing particular features and trends in complex mixing processes, and that analyses using these new properties compare favourably with conventional approaches.

Heat capacities, order–disorder transitions, and thermodynamic properties of rare-earth orthoferrites and rare-earth iron garnets

Rare-earth orthoferrites, RFeO 3, and rare-earth iron garnets (RIGs) R 3Fe 5O 12 ( R=rare-earth elements) were prepared by citrate–nitrate gel combustion method and characterized by X-ray diffraction method. Isobaric molar heat capacities of these oxides were determined by using differential scanning calorimetry from 130 to 860 K. Order–disorder transition temperatures were determined from the heat capacity measurements. The Néel temperatures ( T N) due to antiferromagentic to paramagnetic transitions in orthoferrites and the Curie temperatures ( T C) due to ferrimagnetic to paramagnetic transitions in garnets were determined from the heat capacity data. Both T N and T C systematically decrease with increasing atomic number of R across the series. Lattice, electronic and magnetic contributions to the total heat capacity were calculated. Debye temperatures as a function of absolute temperature were calculated for these compounds. Thermodynamic functions like C p , m o , S m o , H o, G o, ( H T o - H 0 o ) , ( H T o - H 298.15 K o ) , - ( G T o - H 298.15 K o ) / T , Δ f H m o , and Δ f G m o have been generated for the compounds RFeO 3(s) and R 3Fe 5O 12(s) based on the experimental data obtained in this study and the available data in the literature.

Density and Heat Capacity as a Function of Temperature for Binary Mixtures of 1-Butyl-3-methylpyridinium Tetrafluoroborate + Water, + Ethanol, and + Nitromethane

Experimental measurements of density and isobaric molar heat capacity for the binary systems containing ionic liquid 1-butyl-3-methylpyridinium tetrafluoroborate + water, + ethanol, and + nitromethane are presented within the temperature range (293.15 to 318.15) K at atmospheric pressure. From these data, excess molar volumes and excess molar isobaric heat capacity are calculated and discussed based on arguments often used for the study of liquid mixtures.

Heat capacities of the mixtures of ionic liquids with methanol at temperatures from 283.15 K to 323.15 K

The molar isobaric heat capacities of (methanol+1-hexyl-3-methylimidazolium tetrafluoroborate) and (methanol+1-methyl-3-octylimidazolium tetrafluoroborate) mixtures have been determined over the temperature range from 283.15K to 323.15K within the whole composition range. The excess molar heat capacities of investigated mixtures have been fitted to the Redlich–Kister equation at several selected temperatures. Positive deviations from the additivity of molar heat capacities have been observed in both examined systems. The results obtained have been discussed in terms of molecular interactions in binary mixtures.

The system H 2O–NaCl. Part II: Correlations for molar volume, enthalpy, and isobaric heat capacity from 0 to 1000 °C, 1 to 5000 bar, and 0 to 1 XNaCl

A set of correlations for the volumetric properties and enthalpies of phases in the system H 2O–NaCl as a function of temperature, pressure, and composition has been developed that yields accurate values from 0 to 1000 °C, 1 to 5000 bar, and 0 to 1 X NaCl. The volumetric properties of all fluid phases from low-density vapor to hydrous salt melts and single-phase binary fluids at high pressures and temperatures, can be described by a simple equation V solution ( T , P , X NaCl ) = V H 2 O ( n 1 + n 2 T , P ) i.e., for a given pressure and composition, the molar volume of the solution is related to the molar volume of pure water at the same pressure by a linear scaling of temperature. The parameters n 1 and n 2 are simple functions of pressure and composition. This linear relation could be demonstrated for all ( P, X NaCl) pairs where accurate volumetric data are available over a sufficiently large temperature interval. Extrapolations over as much as 300 °C predict high temperature data within their experimental uncertainty of 1–2%. With a simple fit of parameters n 1 and n 2, the vast majority of several thousand experimental data points from the literature can be reproduced within experimental error, including dilute solutions in the compressible region. Although a strict theoretical foundation is lacking, this behavior can phenomenologically be rationalized as reflecting the relation between the linear to near-linear isochores of binary fluids to those of pure water. Accordingly, small deviations from linearity that amount to 0.1–0.2% error in molar volume occur only at low temperatures where the pure water isochores behave non-linearly. This effect is accounted for by introducing a deviation function. Given its high accuracy, the formulation for the molar volumes could be integrated along isotherms–isobars to generate data for the specific enthalpy of binary solutions. In order to allow direct computation rather than numerical integration, a correlation scheme was developed that is mathematically similar to that for molar volumes. Specific enthalpies computed from the correlation typically agree within 1–3% with those obtained from other studies. Similarly, isobaric heat capacities show good agreement with published data except for high salinities at moderate pressures and temperatures.

Molar heat capacities for (1-butanol + 1,4-butanediol, 2,3-butanediol, 1,2-butanediol, and 2-methyl-2,4-pentanediol) as function of temperature

The isobaric molar heat capacities for the binary mixtures (1-butanol + 1,4-butanediol) were determined in the temperature range from (293 to 353) K from measurements of isobaric specific heat capacity in a differential scanning calorimeter. The composition dependencies of the excess molar isobaric heat capacities obtained from the experimental results were fitted by the Redlich–Kister polynomials. Above T = 303.15 K, the excess isobaric molar heat capacities are negative over the whole composition range and absolute values increase with temperature. For temperatures (293.15 and 298.15) K, the excess values show S-shaped character. These excesses are however in general very small; at the temperature 298.15 K smaller than 0.1 J · K −1 · mol −1. Additionally, the isobaric molar heat capacities of 2,3-butanediol, 1,2-butanediol, and 2-methyl-2,4-pentanediol were determined over a similar temperature range. The experimental data for all diols are compared with available literature data and values estimated from group additivity.

Highly precise experimental device for determining the heat capacity of liquids under pressure

An experimental device for making isobaric heat capacity measurements of liquids under pressure is presented. The device is an adaptation of the Setaram micro-DSC II atmospheric-pressure microcalorimeter, including modifications of vessels and a pressure line allowing the pressure in the measurement system to be set, controlled, and stabilized. The high sensitivity of the apparatus combined with a suitable calibration procedure allows very accurate heat capacity measurements under pressure to be made. The relative uncertainty in the isobaric molar heat capacity measurements provided by the new device is estimated to be 0.08% at atmospheric pressure and 0.2% at higher levels. The device was validated from isobaric molar heat capacity measurements for hexane, nonane, decane, undecane, dodecane, and tridecane, all of which were highly consistent with reported data. It also possesses a high sensitivity as reflected in its response to changes in excess isobaric molar heat capacity with pressure, which were examined in this work for the first time by making heat capacity measurements throughout the composition range of the 1-hexanol+n-hexane system. Finally, preliminary measurements at several pressures near the critical conditions for the nitromethane+2-butanol binary system were made that testify to the usefulness of the proposed device for studying critical phenomena in liquids under pressure.

Thermodynamics of Mixing Tetrahydropyran with 1-Alkanols and Excess Enthalpies of Homomorphy-Related Systems

Densities (ρ) and volumetric heat capacities (Cp/V) have been measured at 298.15 K over the whole mole fraction range for the binary mixtures {tetrahydropyran + 1-propanol, + 1-butanol, + 1-pentanol, + 1-hexanol, + 1-heptanol, + 1-octanol, + 1-nonanol, or + 1-decanol}. From experimental data, the excess molar isobaric heat capacities ( ) were calculated. Excess molar volumes (VE) are reported for the systems containing 1-propanol, 1-butanol, 1-pentanol, and 1-decanol. In order to assess and compare the different degrees of hetero-association in these mixtures, the corresponding negative enthalpic contributions at equimolar fraction (Hint) have been calculated semiquantitatively by using the apolar homomorph concept. With this aim, excess molar enthalpies (HE) of {tetrahydropyran + 1-pentanol, + 1-nonanol, or + 1-decanol}, {tetrahydropyran + decane}, and {cyclohexane + 1-pentanol, + 1-heptanol, + 1-nonanol, or + 1-decanol} have been measured at 298.15 K. The results are discussed in terms of molecular inte...

Thermodynamic properties of CaTiF 5(s)

Calcium titanofluoride CaTiF 5(s) was prepared by solid-state reaction of CaF 2(s) with TiF 3(s) and characterized by X-ray diffraction method. The standard molar isobaric heat capacity ( C p ,m ∘ ) of CaTiF 5(s) was determined by a power compensated differential scanning calorimeter in the temperature from 230 K to 710 K. A solid-state galvanic cell with CaF 2 as electrolyte was used to determine the standard molar Gibbs energy of formation ( Δ f G m ∘ ) of CaTiF 5 in the temperature range from 803 K to 1005 K. The galvanic cell can be depicted as: ( - ) Pt, O 2 ( g, 101.325 kPa ) / { CaO(s) + CaF 2 ( s ) } / / CaF 2 / / { CaTiF 5 ( s ) + CaTiO 3 ( s ) } / O 2 ( g, 101.325 kPa ) ,Pt ( + ) The second law analysis of present data were carried out to derive the standard entropy S m ∘ ( 298.15 K ) and the enthalpy of formation Δ f H m ∘ ( 298.15 K ) and the values derived are 68.7 J · K −1 · mol −1 and −2848.4 kJ · mol −1, respectively.