Enthalpy Coefficients Research Articles

Measurement and modeling the excess molar properties of binary mixtures of {[C6mim][BF4] + 3-amino-1-propanol} and {[C6mim][BF4] + isobutanol}: Application of Prigogine–Flory–Patterson theory

In this work, densities, ρ, and viscosities, η, of pure 1-hexyl-3-methylimidazoliumtetrafluoro borate {[C6mim][BF4]}, 3-amino-1-propanol (AP), and isobutanol, along with their binary mixtures of {x1[C6mim][BF4]+x2AP} and {x1[C6mim][BF4]+x2isobutanol} were measured over entire composition range at ambient pressure (81.5kPa) and in the temperature range of (303.15 to 338.15)K. The excess molar volume, VmE, thermal expansion coefficient, α, and its excess value, αE, isothermal coefficient of excess molar enthalpy, (∂HmE/∂p)T,x, and viscosity deviation, Δη, for both of the mixtures were calculated from the experimental values of densities and viscosities. The values of VmE for binary mixture of {x1[C6mim][BF4]+x2AP} shows a S-shaped dependence on composition with positive values in the [C6mim][BF4] rich-region and negative values at the opposite extreme, and increase with increasing temperature. This quantity is negative for binary mixture of {x1[C6mim][BF4]+x2isobutanol} in the entire composition range and increases with increasing temperature. Viscosity deviations, Δη, are negative over the entire composition range and decrease with increasing temperature for both of the mixtures. These data were correlated by Treszczanowiczb–Benson and Redlich–Kister equations, and the fitting parameters and standard deviations were determined. The Prigogine–Flory–Patterson theory has been used to correlate the excess molar volumes of the mixtures.

Thermodynamic properties of Laves phases in the Mg–Al–Ca system at finite temperature from first-principles

First-principles calculations are employed to investigate the structural and thermodynamic properties of binary Laves phases (C14, C15 and C36 structures) in the Mg–Al–Ca system. The enthalpies of formation at 0 K are predicted. The vibrational contributions to Helmholtz free energy for the stable C14-Mg 2Ca and C15-Al 2Ca phases are determined using both first-principles phonon calculations and Debye–Grüneisen model. The predicted thermodynamic properties of the stable phases, including enthalpy, entropy, bulk modulus, heat capacity, and thermal expansion coefficient, agree well with available experimental data. For the other nonstable phases, the thermodynamic properties are estimated by Debye–Grüneisen models of Moruzzi et al. and of Wang et al. The entropies predicted from these two Debye models have a general agreement with about ±0.5 J/mol K differences for all the three structures.

Heat sensitivity of vertical water wall at low mass velocity in supercritical pressure W-shaped flame boiler

The vertical water wall of the once-through boiler is sensitive to heat disturbance because of its smaller water volume compared with the drum boiler. This paper deduced formulas of the sensitivity coefficient of flow and output enthalpy, and made a heat sensitivity analysis for the vertical water wall of a 600 MW supercritical pressure W-shaped flame boiler at a low mass velocity when heat disturbance occurs. It was found that the flow sensitivity coefficient decreases and the outlet enthalpy sensitivity coefficient increases with increasing steam quality. Increasing mass velocity weakens the flow sensitivity and enhances the outlet enthalpy sensitivity. When the mass velocity exceeds a certain value, the flow sensitivity coefficient is less than zero. Increasing heat flux leads to an increase in the flow sensitivity coefficient and a decrease in the outlet enthalpy sensitivity coefficient. In the condition of low steam quality, the flow sensitivity weakens and outlet enthalpy sensitivity strengthens when the pressure is up to 22 MPa. Moreover, when the quality is high, rising pressure strengthens the flow sensitivity and weakens the outlet enthalpy sensitivity. The study has provided some instructive findings, which may be helpful for the safety operation of the 600 MW supercritical pressure W-shaped flame boiler.

Thermodynamic study of binary mixture of x1[C 6mim][BF 4] + x21-propanol: Measurements and molecular modeling

Densities, ρ, and viscosities, η, of pure 1-hexyl-3-methylimidazoliumtetrafluoro borate ([C 6mim][BF 4]) and 1-propanol, and their binary mixture { x 1[C 6mim][BF 4] + x 21-propanol} were measured at atmospheric pressure and in the temperature range of 293.15–333.15 K. The excess molar volumes, V m E , thermal expansion coefficients, α, and their excess values, α E , isothermal coefficient of excess molar enthalpy, ( ∂ H m E / ∂ p ) T , x and excess viscosities, η E , were calculated from the experimental values of densities and viscosities. The excess molar volumes of the binary mixture are negative over the entire mole fraction range and increase with increasing temperature. Excess viscosities are negative over the entire mole fraction range of the mixture and decrease with increasing temperature. The obtained excess molar volumes and excess viscosities were correlated with the Redlich–Kister equation. The experimental results have also been used to examine the applicability of Prigogine–Flory–Patterson (PFP) theory in predicting the excess molar volume of the binary mixture. It is indicated that agreement between excess molar volumes calculated via PFP theory and the experimental results is good in all temperatures.

The theoretical study of effect of temperature on the physicochemical parameters for binary mixtures of vinyl acetate and benzyl acetate, + o-xylene, + m-xylene and + p-xylene

In this work we used the Flory theory of liquid mixtures for determining the thermal parameters such as excess thermal expansion coefficients αE, and isothermal coefficient of pressure excess molar enthalpy (∂HmE/∂P)T,x, of the binary mixtures formed by vinyl acetate and benzyl acetate+o-xylene, or m-xylene, or p-xylene at (303.15 and 313.15)K. From these data the acoustical parameters such as available volume (Va), isothermal (K/), isobaric (K), and isochoric acoustical parameters (K//), isochoric temperature coefficient of the internal pressure (X), and Moelwyn-Hughes parameter (C1), have been calculated. The excess thermal expansion coefficient αE, for the binary mixtures of benzyl acetate+o-xylene and vinyl acetate+m-xylene are negative in x=0.2434 and x=0.9602, respectively, and positive for all mole fractions and increase with increasing temperatures from (303.15 and 313.15)K. The isothermal coefficient of pressure excess molar enthalpy, (∂HmE/∂P)T,x, for vinyl acetate+o-xylene, +p-xylene and benzyl acetate+m-xylene,+p-xylene are negative and decrease with increasing temperatures from (303.15 and 313.15)K. The isothermal coefficient of pressure excess molar enthalpy, (∂HmE/∂P)T,x, for a binary mixture of benzyl acetate+o-xylene is positive and increases with increasing temperatures from (303.15 and 313.15)K.

Influence of the composition of aqueous-alcohol solvents on the thermodynamic characteristics of l-phenylalanine dissolution at 298.15 K

The enthalpies of l-phenylalanine dissolution in aqueous methanol, ethanol, 1-propanol and 2-propanol have been determined by calorimetry at 298.15 K and alcohol mole fractions up to x 2 ∼0.4. The standard enthalpies of solution Δ sol H° and transfer Δ tr H° from water to the mixed solvent as well as the enthalpy coefficients of l-phenylalanine–alcohol pair-wise interactions were calculated. The interrelation of the enthalpies of dissolution and transfer for l-phenylalanine with structural features of alcohols has been determined. A comparative analysis of the thermodynamic characteristics of dissolution of l-phenylalanine and some other amino acids (glycine, l-alanine, l-threonine and l-valine) in the mixtures studied has been made.

Effect of organic co-solvents on the solvation enthalpies of amino acids and dipeptides in mixed aqueous solutions

Transition enthalpies (ΔtrHo) of substances from water to binary solutions were calculated at 298.15 K on the basis of standard dissolution enthalpies (ΔsolHo) for six amino acids and five dipeptides in the mixtures of water with organic solvents of various chemical natures. The enthalpy pair coefficients of interaction hxy for biomolecules with organic component of mixture were estimated within the formalism of the McMillan-Mayer theory. The change in the character of the interaction of the components of solution was demonstrated in dependence on the physicochemical properties of the solvent and nature of the side radical of the dissolved bioorganic substance. Quantitative estimation of the type of interaction of the substance with the solvent was performed on the basis of correlation ratios relating the enthalpy characteristics of bioorganic substances to properties of organic cosolvents. It was shown that in the solutions under study, the effects of both the specific (mainly electron donor) and non-specific solvation of amino acids and peptides are observed.

Dependence of enthalpies of dissolution of β-alanyl-β-alanine on the composition of (water + alcohol) mixtures at 298.15 K

The dissolution enthalpies of β-alanyl-β-alanine in aqueous methanol, ethanol, 1-propanol and 2-propanol solutions with an alcohol content up to 0.4 mole fractions have been measured calorimetrically at T = 298.15 K. The standard enthalpies of dissolution, Δ sol H° and transfer, Δ tr H°, of β-alanyl-β-alanine from water into mixed solvents and the enthalpy coefficients of pair-wise interactions, h xy , of β-alanyl-β-alanine with alcohol solvent molecules have been calculated. The results are discussed in terms of solute–solute and solute–solvent interactions.

Enthalpy-related interaction parameters in H/D isotopically distinguishable aqueous solutions of tetramethylurea cyclic derivatives at 298.15 K

The enthalpies for dilution of solutions of 1,1,3,3-tetramethylurea (TMU), 1,3-dimethylethyleneurea (DMEU), 1,3-dimethylpropyleneurea (DMPU) and 2,4,6,8-tetramethyl- bis-urea (TM bU) in ordinary (H 2O) and heavy (D 2O) water were measured calorimetrically at 298.15 K. The enthalpy coefficients for pair ( h 22) and triplet ( h 222) interactions between hydrated solute molecules were estimated using the McMillan–Mayer formalism. The quantities of h 22 as well as the corresponding solvent isotope effects were found to be positive for aqueous TMU, DMPU and DMEU and negative for aqueous TM bU. The correlation between h 22 and standard enthalpies of solution of these compounds in H 2O and D 2O was established at the temperature in question.

Dependence of the solution and transfer enthalpies of DL-α-alanyl-DL-α-asparagine on the composition of water-amide binary solvents at 298.15 K

Solution enthalpies of DL-α-alanyl-DL-α-asparagine (AlaAsn) in water-formamide, water-N-methylformamide, water-N,N-dimethylformamide, and water-N,N-dimethylacetamide mixtures were measured in the range of amide mole fractions x 2 = 0–0.3. The standard enthalpies of solution (Δsol H°) and transfer (Δtr H°) of AlaAsn from water to the binary solvent and enthalpy coefficients of pair-wise interactions (h xy ) of AlaAsn with amide molecules were calculated. The influence of the composition of the water-organic mixture on the enthalpy characteristics of AlaAsn is discussed. It is shown that the enthalpy characteristics of solution and transfer of AlaAsn are related to the structure of amides.

<b>Derived thermodynamic properties of [<i>o</i>-xylene or <i>p</i>-xylene + (acetic acid or tetrahydro-furan)] at different temperatures and pressures</b>

Thermal expansion coefficients α, their excess values , isothermal coefficient of pressure excess molar enthalpy , partial molar volumes and excess partial molar volumes , were calculated from experimental densities. The isothermal coefficients of pressure excess molar enthalpy for binary mixtures { o -xylene or p -xylene + acetic acid} at temperatures 313.15-473.15 K and pressure 0.2-2 MPa are negative and for binary mixtures { o -xylene or p -xylene + tetrahydrofuran (THF)} at temperatures 278. 15 K to 318.15 K and pressure 81.5 kPa are negative and with increasing temperature become more negative. The excess thermal expansions coefficient , for binary mixtures { o -xylene or p -xylene + acetic acid} at temperatures 313.15-473.15 K and pressure 0.2 MPa and 2 MPa are positive. The excess thermal expansions coefficient for binary mixtures { o -xylene or p -xylene + tetrahydrofuran (THF)} at temperatures 278.15-318.15 K and pressure 81.5 kPa are positive and with increasing temperature become more positive. The excess molar volumes were correlated with a Redlich–Kister type equation. KEY WORDS : Thermal expansion coefficients, Isothermal coefficient, Excess partial molar volumes Bull. Chem. Soc. Ethiop. 2011 , 25(2), 273-286.

Enthalpies of solution of glycylglycylglycine in aqueous solution of amides at 298.15 K

Calorimetric measurements have been carried out at 298.15 K in aqueous solutions of glycylglycylglycine containing formamide, N-methylformamide, N, N-dimethylformamide and N, N-diethylformamide at concentrations of amides as co-solvents up to 0.4 mole fractions. The results obtained have been used to calculate the standard enthalpies of solution (Δ sol H°) and transfer (Δ tr H°) of the glycylglycylglycine from water into the mixtures as well as enthalpy coefficients of pair-wise interaction ( h xy ) of the solute with amide in aqueous media. The h xy values were correlated with the properties of organic solvents using Kamlet–Taft equation. The results of the calorimetric measurements have been discussed with regard to the intermolecular interactions occurring in these systems.

Generalized thermodynamic and transport properties. II. Molecular liquids

In the present paper, we extend the method described in paper I [D. Bertolini and A. Tani, preceding paper, Phys. Rev. E 83, 031201 (2011)] to molecular liquids, which allows us to solve the exact kinetic equation proposed by de Schepper et al. [Phys. Rev. A 38, 271 (1988)] without approximations. In particular, generalized thermodynamic properties (enthalpy, specific heat, and thermal expansion coefficient) and transport properties (longitudinal viscosity, thermal conductivity) have been calculated for three liquids of increasing complexity, namely dimethyl sulfoxide, hydrogen fluoride, and SPC/E water. All results have been obtained by the molecular formalism as well as the atomic one, corrected for intramolecular correlations that are due to the models adopted. As done for simple liquids, the coupling between the viscous stress tensor and the energy flux vector has been calculated exactly. We also show that the Markov assumption for the dynamics related to thermal conductivity can only be adopted with caution.

Enthalpies of solution of dl-α-alanyl- dl-α-asparagine in aqueous alcohols at 298.15 K

The enthalpies of solution of dl-α-alanyl- dl-α-asparagine (AlaAsn) were measured in aqueous methanol, ethanol, 1-propanol and 2 -propanol with an alcohol mole-fraction content x 2 (from 0 to 0.4) at 298.15 K. The experimental results were used to calculate the enthalpies of transfer of AlaAsn from water to these mixtures as well as the enthalpy coefficients of pair-wise interactions ( h xy ) between AlaAsn and alcohol molecules in water, according to the McMillan–Mayer's model. The h xy values were found to be positive and increasing in a series methanol < ethanol < 1 -propanol < 2 -propanol.

Kinetic and thermodynamic parameters of β-glucosidase immobilized on various colloidal particles from a paddy soil

To better understanding of enzyme stabilization and the subsequent catalytic process in soil environment, the kinetic and thermodynamic parameters of β-glucosidase immobilized on different-sized colloidal particles from a paddy soil were studied. Higher adsorption and lower desorption of β-glucosidase were found on fine soil colloids, which were attributed to their higher surface area and the large content of iron oxides. Immobilization of β-glucosidase decreased the V max values and increased the K m values, which indicated that the immobilized enzyme has an apparently lower affinity for its substrate due to structural changes of β-glucosidase or less accessibility of substrate to the active site of immobilized enzymes. The values of activation energy ( E a), activation enthalpy (Δ H a) and temperature coefficient ( Q 10) for the immobilized enzymes were smaller than those with free enzyme, implying that the immobilized enzymes are less temperature sensitive. Furthermore, mean values of Q 10 were ranged from 1.32 to 1.50. These results indicated the higher stability of β-glucosidase after immobilization on various soil colloidal particles.

Thermophysical properties of seawater: a review of existing correlations and data

Correlations and data for the thermophysical properties of seawater are reviewed. Properties examined include density, specific heat capacity, thermal conductivity, dynamic viscosity, surface tension, vapor pressure, boiling point elevation, latent heat of vaporization, specifi c enthalpy, specific entropy and osmotic coefficient. These properties include those needed for design of thermal and membrane desalination processes. Results are presented in terms of regression equations as functions of temperature and salinity. The available correlations for each property are summarized with their range of validity and accuracy. Best-fi tted new correlations are obtained from available data for density, dynamic viscosity, surface tension, boiling point elevation, specifi c enthalpy, specific entropy and osmotic coefficient after appropriate conversion of temperature and salinity scales to the most recent standards. In addition, a model for latent heat of vaporization is suggested. Comparisons are carried out amo...

Measurement and Prediction of Vapor−Liquid Equilibrium of Aqueous 1-Ethyl-3-methylimidazolium-Based Ionic Liquid Systems

Isothermal vapor−liquid equilibria were determined for two binary ionic liquid + water systems, from 323.3 to 368.2 K, and water mole fractions greater than 0.5. The ionic liquids used were 1-ethyl-3-methylimidazolium trifluoromethanesulfonate and 1-ethyl-3-methylimidazolium trifluoroacetate. In addition, predictive thermodynamic modeling of the vapor−liquid equilibrium was performed by correlating the nonrandom two-liquid,(39) universal quasi-chemical,(40) and electrolyte-NRTL(41) models to previously measured excess enthalpy and infinite dilution activity coefficient data from the literature. For each of the systems studied at least two of the models provided adequate predictions of vapor pressure and water activity coefficients. The good predictions of vapor−liquid equilibria by these common activity coefficient models lead us to favor excess enthalpy and infinite dilution activity coefficient data over vapor−liquid equilibria data, since predictions of excess enthalpies from vapor−liquid equilibria are not satisfactory.

Enthalpies of l-threonine dissolution in some aqueous amides at 298.15 K

The enthalpies of l-threonine dissolution in aqueous formamide, N-methylformamide, N, N-dimethylformamide and N, N-dimethylacetamide were determined by calorimetry at 298.15 K and amide mole fractions up to x 2 ∼ 0.3. The standard enthalpies of solution Δ sol H° and transfer Δ tr H° from water to the mixed solvent as well as the enthalpy coefficients of l-threonine–amide pairwise interactions were calculated. The interrelation of the enthalpies of dissolution and transfer for l-threonine with structural features of each of aqueous amides was determined.

Enthalpies of solution of glycylglycine in water–organic solvent media at 298.15 K

The enthalpies of solution of glycylglycine in aqueous solution of 1,4-dioxane, acetone, formamide, N-methylformamide and N,N-dimethylformamide, with the co-solvent content up to 0.4 mole fractions, have been measured calorimetrically at T = 298.15 K. The results obtained were used to calculate the standard enthalpies of solution (Δ sol H°) and transfer (Δ tr H°) of the glycylglycine from water into the mixtures as well as the enthalpy coefficients of pair-wise interaction h xy of the solute with the organic co-solvents in aqueous media. The h xy values were correlated with the properties of organic solvents using the Kamlet–Taft equation. The effect of the structure properties of the mixed solvent on the specified enthalpy characteristics of glycylglycine is discussed.

Excess thermodynamic parameters of binary mixtures of methanol, ethanol, 1-propanol, and 2-butanol + chloroform at (288.15–323.15 K) and comparison with the Flory theory

In this work we used the experimental result for calculating the thermal expansion coefficients α, and their excess values α E , and isothermal coefficient of pressure excess molar enthalpy and comparison the obtain results with Flory theory of liquid mixtures for the binary mixtures {methanol, ethanol, 1-propanol and 2-butanol-chloroform} at 288.15, 293.15, 298.15, 303.15, 308.15, 313.15, 318.15, and 323.15 K. The excess thermal expansion coefficients α E and the isothermal coefficient of pressure excess molar enthalpy ((∂H m E /∂P) T,x for binary mixtures of {methanol and ethanol + chloroform} are S-shaped and for binary mixtures of {1-propanol and 2-butanol + chloroform} are positive over the mole fraction. The isothermal coefficient of pressure excess molar enthalpy (∂H m E /∂P) T,x , are negative over the mole fraction range for binary mixture of {1-propanol and 2-butanol + chloroform}. The calculated values by using the Flory theory of liquid mixtures show a good agreement between the theory and experimental.