Excess Molar Isobaric Heat Capacities Research Articles

Thermophysical and volumetric properties of mixtures {carvacrol + ethanol} at several temperatures and atmospheric pressure

Experimental molar heat capacities at atmospheric pressure have been determined for the mixture {carvacrol + ethanol} every 10 K in the temperature interval (298.15–328.15) K and over the entire composition range with a Calvet type calorimeter. Densities, necessary for determining isobaric heat capacities, and ultrasonic speed of sound have been also measured at the same conditions. From these properties isobaric thermal expansivities, isentropic compressibilities, isothermal compressibilities, internal pressures and isochoric molar heat capacities have been calculated. Furthermore, in order to complete our thermophysical study the corresponding excess properties have been calculated and discussed in terms of molecular interactions. Finally, excess molar isobaric heat capacities have been calculated with COSMO-RS and compared to the experimental values.

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.

Excess volumes and excess heat capacities of {1,2-alkanediol + methanol} mixtures and ionic volumes in these systems

Densities of {1,2-propanediol+MeOH}, {1,2-butanediol+MeOH} and {1,2-pentanediol+MeOH} mixtures and densities of dilute solutions of three electrolytes (NaI, NaBPh4 and Ph4PI) in mentioned mixtures with exception the system containing 1,2-pentanediol were measured at T=298.15K. Isobaric specific heat capacities for {1,2-propanediol+MeOH} and {1,2-pentanediol+MeOH} mixtures were measured using a differential scanning calorimeter over the temperature range from (293 to 324) K. The excess molar volumes and excess molar isobaric heat capacities of binary systems were calculated and fitted by the Redlich–Kister polynomials. For ternary systems apparent molar volumes of electrolytes were determined at an electrolyte concentration of 0.025molkg−1 over the entire mixed solvent composition range. Single ionic apparent molar volumes of transfer, ΔtVφ (ion) were calculated using the tetraphenylphosphonium tetraphenylborate (TPTB) assumption. The influence of the carbon–chain length over the obtained functions was studied. The results were analyzed in terms of intermolecular association.

Molar heat capacities for {isomer of butanediol + methanol} as function of mixture composition and temperature

Isobaric specific heat capacities for the binary mixtures {isomer of butanediol+methanol} were measured using a differential scanning calorimeter. The isobaric molar heat capacities were determined in the temperature range from (293 to 324)K. The excess molar isobaric heat capacities of mixtures and its components were calculated. The composition dependencies of the excess molar isobaric heat capacities at T=298.15K and at T=323.15K were fitted by the Redlich–Kister polynomials. The obtained results were analyzed from point of view of the influence of distance of OH groups in butanediol molecule.

Isobaric, isothermal theoretical investigation and examination of different prediction equations on some physicochemical properties in PEG liquid polymer system

Densities, viscosities and refractive indices of the {poly(ethylene glycol) 200+ethanol} binary liquid system were determined at three temperatures of (298.15, 303.15, and 308.15)K. From the experimental results, the excess molar volume was obtained and correlated with the Prigogine–Flory–Patterson (PFP) and Extended Real Associated Solution (ERAS) models. Several isobaric and isothermal properties consisting of the isobaric thermal expansion coefficient, excess molar isobaric expansion, excess molar isobaric heat capacity, isothermal coefficient of excess molar enthalpy, activation energy of flow, electron polarizibility, and Gibbs energy of activation were calculated from the experimental measurements. Moreover, the viscosity and refractive index values were correlated and predicted with different semi-empirical equations. To assess the validity of these proposed equations, comparisons were made between the experimental and predicted values.

Excess volumes and excess heat capacities for alkanediol + water systems in the temperature interval (283.15–313.15) K

Density and isobaric heat capacity per unit volume were determined for aqueous mixtures of 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, and 1,2-hexanediol over the whole composition range in the temperature interval (283.15–313.15)K at atmospheric pressure. From these data, excess molar volumes and excess isobaric molar heat capacities were obtained. The comparison of experimental data with literature values shows quite good agreement, not only for absolute magnitudes, but also for excess quantities. Excess volumes are negative over the whole composition range and they become more ideal (less negative) as temperature increases. Excess isobaric molar heat capacity is mostly positive, although it is negative for some mixtures at several compositions and temperatures. Moreover, it was found that it presents a maximum at low mole fraction of the alcohol for most systems, as it was previously found for alkanol+water mixtures. As for temperature dependence, excess isobaric molar heat capacity increases with raising temperature in all cases. This increase is more pronounced for concentrated solutions of dialcohol, with the exception of the 1,2-hexanediol system. The obtained results are interpreted in terms of well-known arguments based on definition of excess magnitudes and chemical nature of the compounds.

Thermodynamics of 1-alkanol + linear polyether mixtures

Experimental densities, ρ, and speeds of sound, u, have been measured at (293.15–303.15)K for the systems methanol, 1-butanol or 1-decanol+3,6,9-trioxaundecane using a vibrating-tube densimeter and sound analyzer Anton Paar model DSA-5000. These values were used to calculate excess molar volumes, VmE, excess adiabatic compressibilities, κSE, and excess speeds of sound, uE. Data available in the literature on excess molar enthalpies, HmE, and on excess molar isobaric heat capacities, Cp,mE, of 1-alkanol+linear polyether mixtures indicate that: (i) interactions are mainly of dipolar type, particularly for solutions with longer 1-alkanols; (ii) the ability of the ether to break the alcohol self-association increases with the number of CH2CH2O groups in the oxaalkane. The enthalpies of the alcohol-ether interactions, ΔHOH−O, have been determined. In mixtures with a given polyether, ΔHOH−O increases with the alcohol size. For 1-alkanol+CH3O(CH2CH2O)nCH3 systems, ΔHOH−O decreases for increased n values. Alcohol-ether interactions are stronger in mixtures with linear polyethers than in those with monoethers.VmE data show the existence of free volume effects in solutions including methanol or ethanol. These effects become more important for large n values, which is supported by values of ∂VmE∂TP. The Flory model has been used to investigate orientational effects in the systems under study. It is shown that orientational effects are relevant in mixtures with methanol or ethanol, and that the behaviour of the remaining systems is close to that of random mixing. Solutions with 3,6-dioxaoctane slightly differ from this trend and are characterized by weak orientational effects. We have also applied the Flory model to 1-alkanol+PEG-250, or +PEG-350 mixtures, which behave similarly to those including linear polyethers. Orientational effects are much stronger in 1-alkanol+linear monoether systems, and are roughly independent of the mixture components. Results obtained in this work are consistent with those obtained previously when applying the Kirkwood–Buff formalism.

Thermodynamics of alkanone + aromatic hydrocarbon mixtures

Linear alkanone or cyclohexanone+aromatic hydrocarbon mixtures have been studied using DISQUAC and the Kirkwood–Buff formalism. The aromatic compounds considered are: benzene, toluene, 1,4-dimethylbenzene, 1,2,4-trimethylbenzene and ethylbenzene. Vapour–liquid equilibria (VLE), molar excess Gibbs energies, GmE, molar excess enthalpies, HmE, and isobaric molar excess heat capacities, CpmE, of the binary systems studied are well represented by DISQUAC. There is a good agreement between experimental HmE values of related ternary mixtures, and DISQUAC predictions obtained by means of binary interaction parameters only DISQUAC improves very meaningfully UNIFAC results on HmE, CpmE, properties which are closely related to the molecular structure of the mixture components. The enthalpy (HintCO-S) of the ketone–aromatic hydrocarbon interactions has been evaluated. These interactions become weaker when the alkanone size increases in mixtures with a given aromatic hydrocarbon, or when the aliphatic surface of the alkylbenzene is increased in systems with a given ketone. Steric effects are more relevant in 1,4-dimethylbenzene mixtures than in those with ethylbenzene. The application of the Kirkwood–Buff formalism to mixtures including toluene or ethylbenzene shows that orientational effects, related to ketone–ketone interactions, exist in solutions with the shorter 2-alkanones. Such effects are weakened when the chain length of the 2-alkanone increases. The opposite behaviour is observed when increasing the aliphatic surface of the alkylbenzene in systems with a given 2-alkanone. The cyclohexanone+benzene mixture shows a structure close to random mixing.

Water structure enhancement in water-rich binary solvent mixtures. Part II. The excess partial molar heat capacity of the water

The excess partial molar isobaric heat capacity of water, C PW E, in water-rich mixtures with co-solvents has been calculated. When the excitation of internal modes of the water molecules is deducted in part, the remainder indicates, if positive, that the relative extent of fully hydrogen bonded domains of the water is enhanced. This was demonstrated in the cases of aqueous methanol, ethanol, 1- and 2-propanol, t-butanol, 2-methoxyethanol, 1,2-dimethoxyethane, tetrahydrofuran, acetone, N,N-dimethylformamide, and N,N-dimethylacetamide. Some solutes such as ethylene glycol, 1,4-dioxane, acetonitrile, N-methylformamide, formamide (and urea), ethanolamine, and dimethylsulfoxide, many of which hydrogen-bond very strongly with water, do not enhance the water structure according to this criterion. The results are compared qualitatively with conclusions from the partial molar excess volumes of the solutions and these agree with the present ones.

Volumes, Heat Capacities, and Compressibilities of the Mixtures of Acetonitrile with N,N-Dimethylacetamide and Propylene Carbonate

The densities of the mixtures of acetonitrile and N,N-dimethylacetamide or propylene carbonate were measured within the whole composition range of the systems at temperatures (308.15 and 318.15) K, while the isobaric heat capacity and speed of sound in these mixtures were measured within the whole composition range at 298.15 K. The results obtained were used to calculate the excess molar volume and isobaric heat capacity and the partial molar volumes and heat capacities of both components of the mixtures as well as the adiabatic (κS) and isothermal (κT) compressibility and their excess. The internal pressures of the systems were also calculated. The results have been analyzed and discussed.

Measurements of Density and Heat Capacity for Binary Mixtures {x Benzonitrile + (1 −x) (Octane or Nonane)}

Densities and isobaric heat capacities per unit volume have been measured for binary mixtures {x benzonitrile + (1 − x) octane} and {x benzonitrile + (1 − x) nonane} in the temperature ranges of (283.15 to 318.15) K and (283.15 to 313.15) K, respectively. Measurements covered the whole composition range at the ambient pressure. From these measured data, the excess molar volumes, excess isobaric thermal expansivities, and excess isobaric molar heat capacities were calculated and fitted with the Redlich−Kister equation. The excess molar volumes, excess isobaric thermal expansivities, and excess isobaric molar heat capacities of both systems were found to exhibit the S-shaped curves against the composition and the feature of the nonrandomness mixing. The dependences of these properties on the temperature and composition were analyzed and discussed in terms of the natures of the two pure components and the molecular interactions in the mixtures.

Solution thermodynamics near the liquid–liquid critical point. II. Excess second-order derivatives

We present a comprehensive study of the behaviour of excess second-order derivatives of binary mixtures near the liquid–liquid critical point. Specifically, excess (isobaric and isochoric) molar heat capacities ( c p , x E and c V , x E ), excess (isothermal and isentropic) compressibilities ( κ T , x E and κ S , x E ), and excess isobaric thermal expansivities ( α p , x E ) have been determined over the whole composition ( x) range at atmospheric pressure and in the homogeneous region within (293.15–323.15) K. Results are consistent with the predictions of the current theory of critical phenomena. Remarkably, anomalous α p , x E ( x ) and κ T , x E ( x ) curves in the critical region are observed. Such anomalies, which are reported here for the first time, are of significant size for α p , x E and very mild in the case of κ T , x E ( x ) , thereby indicating that volumetric effects at near-liquid–liquid criticality are, as expected, very small.

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.

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.

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.

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.

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.

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...