Experimental Enthalpy Data Research Articles

Modeling of experimental excess molar enthalpy with Wilson, UNIQUAC, and NRTL for mixtures of acetophenone with chloro derivatives of ethane and ethene at T = 298.15 K

The excess molar enthalpy HmE, was determined for systems consisting of acetophenone with chloro alkanes and alkenes derivatives. These derivatives include 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane, trichloroethene and tetrachloroethene at a temperature of T = 298.15 K. The Redlich-Kister relation fitting was used to analyze the HmE values obtained from this experimental data. Additionally, the excess partial molar enthalpy HiE was derived from the experimental HmE values. The intermolecular interaction function such as ∂HiE∂xi and ∂HjE∂xjwere also calculated. For the system consisting of acetophenone + 1,1,1-trichloroethane or + tetrachloroethene, the HmE values were found to be positive. Conversely, the HmE values for acetophenone + 1,2-dichloroethane or + 1,1,2,2- tetrachloroethane or + trichloroethene were observed to be negative. The magnitude of the HmE values increased in chloroethanes as the number of chlorine atoms increased, and became more negative in chloroethenes. Based on the local composition theory, the Wilson model, the universal quasichemical (UNIQUAC) model, and the non-random two-liquid (NRTL) model were used to correlate these thermodynamic data. The results showed good agreement with the experimental enthalpy data.

Dissolution of sulfur dioxide and nitrogen monoxide in water

Sulfur dioxide (SO2) and nitrogen monoxide (NO) are some of the gas impurities present in the carbon dioxide (CO2) separated from fume using post combustion capture process. Even in a small amount, these impurities may have an impact on storage process development. The dissolution of such gases in aqueous phase is part of the studies carried out to develop processes and analyse the risks in case of geological storage. The enthalpies of solution of SO2 and NO in water were here investigated by calorimetry, using a flow calorimetric technique. The enthalpies of solution were determined at 323.15 K and 373.15 K for sulfur dioxide, and at 323.15 K for nitrogen monoxide. The experimental enthalpy data were used together with available solubility data to test thermodynamic models representative of vapour-liquid equilibrium.

Modeling Superionic Behavior of Plutonium Dioxide

AbstractThe Bredig transition to the superionic phase indicated with the $$\lambda $$-peak in $${C_p}$$ was highly expected for plutonium dioxide ($${\rm{Pu}}{{\rm{O}}_2}$$) as other actinide dioxides. However, least-square fit and local smoothing techniques applied to the experimental enthalpy data of PuO2 in 1980s could not detect a $$\lambda $$-peak in specific heat that might be due to too scattered and insufficient experimental data. Therefore, this issue has not been yet put beyond the doubts. In the current article, a superionic model of $${\rm{Pu}}{{\rm{O}}_2}$$ is developed with partially ionic model of a rigid ion potential. Thermophysical properties were calculated in constant pressure–temperature ensemble using molecular dynamics simulation. The Bredig transition with vicinity of a $$\lambda $$-peak in specific heat was successfully observed for the model system at about 2,100 K. Moreover, the experimental enthalpy change was well reproduced before and after the estimated transition temperature.

Modeling Superionic Behavior of Plutonium Dioxide

The Bredig transition to the superionic phase indicated with the lambda-peak in Cp was highly expected for PuO2 as other actinide dioxides. However, least-square fit and local smoothing techniques applied to the experimental enthalpy data of plutonium dioxide in 80's could not detect a lambda-peak in specific heat that might be due to too scattered and insufficient experimental data. Therefore, this issue has not been yet put beyond the doubts. In the current article, a superionic model of PuO2 is developed with partially ionic model of a rigid ion potential. Thermophysical properties were calculated in constant pressure-temperature ensemble using molecular dynamics simulation. The Bredig transition with vicinity of a lambda-peak in specific heat was a successfully observed for the model system at about 2100K. Moreover, the experimental enthalpy change was well reproduced before and after the estimated transition temperature.

High Temperature Phase Stability and Heat Capacity of Fe‐0.28Mn‐0.55Si‐0.045C (Mass%) Magnetic Alloy: A Calorimetric Study

The high temperature thermal stability, phase transformation characteristics and heat capacity of a Fe‐0.28Mn‐0.55Si‐0.045C (mass%) magnetic iron base alloy have been investigated by dynamic and drop calorimetry techniques. Upon slow heating, the following phase changes are found to take place: αferro + (Fe,Mn)3C → αpara + (Fe,Mn)3C → α + γ → γ → γ + δ → δ → δ + L → L; with distinct enthalpy effects. The α → γ transformation taking place upon slow heating is appreciably influenced by the dissolution kinetics of (Fe,Mn)3C phase. Enthalpy increment values were measured as a function of temperature, up to 1523 K by drop calorimetry. It is found that magnetic effects play a significant role in influencing overall thermodynamic stability. The experimental enthalpy data have been modeled using Debye–Grüneisen and Hillert–Jarl formalisms for accounting respectively the vibrational and magnetic contributions to heat capacity.

Experimental values and correlations of some thermal properties of fresh and osmotically dehydrated stone fruits

Nectarines, plums and peaches were dehydrated with osmotic solutions (glucose at 60°Brix or sorbitol at 60°Brix) at temperature of 35°C for scheduled periods (0.5, 1, 2, 4, 6, 8 h). Thermal properties of fresh and osmotically dehydrated fruits were measured by DSC where samples were heated from −40°C to 40°C at a rate of 2°C min−1. In this work, we obtained experimental data on the variation of water content and soluble solids during the osmotic dehydration of nectarines, peaches and plums in solutions of glucose or sorbitol; experimental data for enthalpy of fresh and osmotically dehydrated nectarines, plums and peaches as a function of temperature and type of osmotic solute; correlations for initial freezing temperature of osmotically dehydrated stone fruits as a function of water content and type of dehydrating solute and correlations between heat capacity or enthalpy and temperature for some fresh and osmotically dehydrated stone fruits.

New Group-Contribution Approach to Thermochemical Properties of Organic Compounds: Hydrocarbons and Oxygen-Containing Compounds

A new group-contribution approach involving systematic corrections for 1,4-non-bonded carbon-carbon and carbon-oxygen interactions has been proposed. Limits of the applicability of the method, associated with the highly branched structures, were established. Experimental data for enthalpies of formation in the liquid phase, enthalpies of vaporization, and enthalpies of formation in the gas phase for alkanes, alkenes, alkynes, alkylbenzenes, alkanols, ethers, ketones and aldehydes, carboxylic acids, esters, and carbonates were collected and critically evaluated through dynamic data evaluation as implemented in the NIST ThermoData Engine. An automatic procedure for molecular structure “decomposition” was developed, and algorithms for the assessment of expanded uncertainties for the predicted property values were implemented. The combination of these software tools allows for ongoing improvements of the group-contribution parameter set as new experimental data become available. Fifty-two group-contribution parameters and their variances were evaluated for the proposed schema. Based on comparison of critically evaluated and predicted data for all classes of compounds studied, the performance of the new group formulation and associated parameters is superior to that originally suggested by Benson and the update by Cohen without an increase in the number of required parameters.

Thermodynamics of protonation of amines in aqueous solutions at elevated temperatures

The dissociation constants, pKa, of monoethanolamine (MEA), N-methyldiethanolamine (MDEA), 2-amino-2-methyl-1-propanol (AMP), 2(2-aminoethyl)etanolamine (AEEA), and piperazine (Pz) were measured by potentiometric titration over the temperature range (298.15 to 363.15)K. Enthalpies of protonation, ΔHp, were measured calorimetrically at temperatures from (298.15 to 393.15)K for MEA, MDEA, and AMP, and from (298.15 to 353.15)K for AEEA and Pz. In addition, the effect of the ionic strength of the solutions on the protonation of MDEA was studied using NaCl as background salt {(0 to 5.5)mol/kg-H2O)}. Correlations for the reaction equilibrium constants for proton dissociation are proposed for the studied amines based on the experimental data from literature and from this work. Both experimental enthalpy data and dissociation constants were used for fitting. The results from this work may be used for thermodynamic modeling of CO2 capture processes using amines.

Correlation between flexibility of chain-like polyelectrolyte and thermodynamic properties of its solution

Structural and thermodynamic properties of the model solution containing charged oligomers and the equivalent number of counterions were studied by means of the canonical Monte Carlo simulation technique. The oligomers are represented as (flexible) freely jointed chains or as a linear (rigid) array of charged hard spheres. In accordance with the primitive model of electrolyte solutions, the counterions are modeled as charged hard spheres and the solvent as dielectric continuum. Significant differences in the pair distribution functions, obtained for the rigid (rod-like) and flexible model are found but the differences in thermodynamic properties, such as, enthalpy of dilution and excess chemical potential, are less significant. The results are discussed in light of the experimental data an aqueous polyelectrolyte solutions. The simulations suggest that deviations from the fully extended (rod-like) conformation yield slightly stronger binding of counterions. On the other hand, the flexibility of polyions, even when coupled with the ion-size effects, cannot be blamed for qualitative differences between the theoretical results and experimental data for enthalpy of dilution.

Effect of Temperature and Moisture Content on Thermal Properties of Four Types of Meat Part Two: Specific Heat & Enthalpy

The specific heat and enthalpy of four different types of meats (Veal, Hashi, Noeimi, and Najdi) were determined in the temperature range of −40 to 40°C and moisture content range of 30–75% (wet basis). The two properties were measured by the modulated differential scanning calorimeter (MDSC). The specific heat increased almost linearly more significantly with the increasing levels of moisture content than temperature. Multiple regression models with high R2 values were developed to correlate specific heat as a function of moisture content. Statistical analysis revealed that moisture content had significant effect on specific heat of meats. Experimental enthalpy data were compared with predictive models from the literature which gave similar results but none of them was suitable to interpret MDSC results in the temperature range of phase change.

Enthalpies of Formation in the Al—Ni—Ru System by Direct Reaction Synthesis Calorimetry.

Abstract The enthalpies of formation of ternary compounds in the Al–Ni–Ru system have been determined by high temperature reaction calorimetry. The composition dependence of the enthalpy of formation and lattice parameter of the compounds with B2 structure were determined in the region of 0.40 ≤ Al ≤ 0.5 mole fraction. Unusual behavior is observed for the composition dependence of the enthalpy of formation suggesting that formation of a miscibility gap in the B2 phase field occurs. For some compositions, the experimental enthalpy data therefore represent the formation enthalpy of the metastable B2 phase.

Enthalpies of formation in the Al–Ni–Ru system by direct reaction synthesis calorimetry

The enthalpies of formation of ternary compounds in the Al–Ni–Ru system have been determined by high temperature reaction calorimetry. The composition dependence of the enthalpy of formation and lattice parameter of the compounds with B2 structure were determined in the region of 0.40 ≤ Al ≤ 0.5 mole fraction. Unusual behavior is observed for the composition dependence of the enthalpy of formation suggesting that formation of a miscibility gap in the B2 phase field occurs. For some compositions, the experimental enthalpy data therefore represent the formation enthalpy of the metastable B2 phase.

Electronic structure and Rietveld refinement parameters of Ti-doped sodium alanates

The structure of Ti-doped sodium aluminum deuteride has been determined using Rietveld refinement of X-ray and neutron powder diffraction data and compared to values for undoped NaAlD4 and NaAlH4. The refined lattice parameters for the tetragonal NaAlD4 structure are found to be a=5.010Å and c=11.323Å, while those of the monoclinic Na3AlD6 structure are a=5.402Å, b=5.507Å, c=7.725Å, and β=89.491°. Results of ab initio calculations of the lattice parameters are within a few percent of the Rietveld-refined values. The generalized gradient approximation (GGA) is found to produce significantly better agreement with the experimental data than the local-density approximation (LDA), which is attributed to a very inhomogeneous distribution of electronic density in the alanates. The Rietveld refinement, LDA, and GGA results for the Al–H bond length in NaAlD4 are 1.626, 1.634, and 1.631Å, respectively. Refined values of the Al–H bond lengths in Na3AlD6, are in agreement within 2% of earlier work on undoped Na3AlD6 [J. Alloy Comp. 299 (1–2) (2000) 101]. The calculated GGA formation energies for the decomposition reactions of NaAlD4 and Na3AlD6 are 33.5 and 49.9kJ/mol of H2, respectively. The corresponding LDA values are significantly higher: 44.6 and 70.3kJ/mol of H2. Comparison with the experimental enthalpy data suggests that the GGA results are in a very good agreement with the measured ΔH [Proceedings of the 1999 DOE Hydrogen Program Annual Peer Review, NREL/CP-570-26938; J. Alloy Comp. 302 (1–2) (2000) 36]. Detailed theoretical analyses of the electronic band structure, valence charge density distribution, and lattice bonding properties are given.

Modelling enthalpy and entropy of pure and mixed refrigerants with an innovative corresponding states method

In this work an original improvement of the Corresponding States technique is developed and a new model, based on a three parameters CS format, is proposed to predict the enthalpy and the entropy of the new generation halogenated alkanes fluids together with some alkanes. Limiting the analysis of the selected fluids to a specific thermodynamic property behaviour, an appropriate conformality approach can be deduced, which allows to set up a predictive model of high accuracy level on a wide range of the enthalpy and entropy surfaces. The fundamentals of the model are innovative scaling parameters deduced from the enthalpy of vaporization and from two dedicated equations, belonging to the selected family of fluids. This allows to set up innovative models following a CS format. Through the introduction of advanced mixing rules, the models can be simply extended to calculate the corresponding properties for mixtures. The proposed models allow also the calculation of VLE for systems of rather regular behaviour. The required inputs for a pure target fluid are an ideal gas isobaric heat capacity correlation, a single value of saturated liquid density and of vaporization enthalpy; if the last one is lacking, a single value of vapor pressure can be alternatively supplied. For non azeotropic mixtures the enthalpy and entropy models are predictive, whereas in case of azeotropy VLE calculations are possibly only applying regressed interaction coefficients. Due to the lack of accurate experimental enthalpy data and to the particular nature of the entropy function, the validation of the models is proposed against fundamental dedicated EoS available, both for pure and mixtures, for a significant number of the studied family of fluids. The predictive character of the proposed approach as well as the high performances reached, make these models particularly suitable for the new families of fluids regarding advanced technological applications.

New Experimental Data for Enthalpy of Reaction and Temperature- and Degree-of-Cure-Dependent Specific Heat and Thermal Conductivity of the Hercules 3501-6 Epoxy System

Measurements of enthalpy of reaction and temperature- and degree-of-cure-dependent specific heat and thermal conductivity are reported for a commercial epoxy resin system (Hercules 3501-6 resin). A Differential Scanning Calorimeter (DSC) was used to determine heat of reaction and specific heat while the line source method was employed for thermal conductivity. The measured heat of reaction of 508±19J/g is compared with conflicting data previously reported by others. Specific heat is reported in the temperature range of 320–550 K and at degrees of cure 20, 40, 74 and 100%. Both raw data and polynomial curve fits are reported. Thermal conductivity is reported in the temperature range of 298–500 K and at degrees of cure 11.5, 51.2 and 100%. These data are found to be independent of degree of cure within experimental error over this range. The data are represented by Ke = (0.202 + 6:122 × 10−3 T− 4:8107 × 10−5 T2 + 1.248 × 10−7 T3− 1.043 × 10−10 T4)(W/mK) The fractional uncertainty (based on two standard deviations) of the measured enthalpy of reaction, specific heat and thermal conductivity is estimated to be less than ±3.7, ±5 and ±11.8%, respectively.

Improved Benson Increments for the Estimation of Standard Enthalpies of Formation and Enthalpies of Vaporization of Alkyl Ethers, Acetals, Ketals, and Ortho Esters

This work was undertaken for the evaluation and revision of group-additivity values necessary for predicting standard enthalpies of formation and enthalpies of vaporization of ethers, acetals, ketals, and ortho esters by means of Benson's group-additivity methodology. The database on the standard molar enthalpies of vaporization has been extended with measurements on several acetals, ketals, and ortho esters using the transpiration method. The standard molar enthalpies of formation of alkyl ethers, acetals, ketals, and ortho esters were derived using the data for the from the literature and the present results for the enthalpies of vaporization or sublimation. The current database of experimental data for enthalpies of formation and enthalpies of vaporization at 298.15 K have been used to reevaluate the values of the Benson's increments for of alkyl ethers, acetals, ketals, and ortho esters. The group-additivity parameters and strain corrections useful in the application of the Benson's correlation are presented in tabular form, together with a description of their evaluation.

Improved Group-additivity Values for the Estimation of the Standard Enthalpies of Formation of Imines and Carboxylic Acids Derivatives

This work has been undertaken for the evaluation and revision of group additivity values necessary for predicting gaseous standard enthalpies of formation of nitrogen and oxygen containing compounds by means of Benson's group additivity methodology. The current database of experimental data for enthalpies of formation, enthalpies of vaporization and enthalpies of sublimation was used to derive the values of the strain-free increments for imines, amides, oxo-amides, and carboxylic acids anhydrides. The group-additivity parameters and strain corrections useful in the application of the Benson correlation are presented in tabular form, together with a description of their evaluation and comments on their reliability.

A Modification of Trouton's Rule by Simple Molecular Parameters for Hydrocarbon Compounds

The entropy of vaporization at the normal boiling point (ΔSb) is an important property in the chemical engineering and environmental sciences. This paper presents a simple modification of Trouton's rule to estimate this property for a variety of hydrocarbon compounds including alkanes, alkenes, alkynes, dienes, cycloalkanes, and alkyl aromatics. The equation contains three easy-to-determine parameters that describe important molecular features: flexibility, symmetry, and planarity. The entropy data were calculated from experimental enthalpy data of 477 different organic compounds at the normal boiling point. The average percentage error for the prediction is 1.30 by the proposed method, 2.79 by Trouton's rule, 1.62 by Kistiakowsky's method, 1.51 by Vetere's method, and 2.23 by the group contribution method of Ma and Zhao.

The Formation Enthalpies of Rare Earth-Aluminum Alloys and Intermetallic Compounds

The enthalpies of formation of rare earth-aluminum alloys and intermetallic compounds have been calculated with Miedema's semi-empirical theory. The calculated enthalpies are in good agreement with experimental enthalpy data and with phase diagram information.

Enthalpies of formation of rare earth-3d metal alloys and intermetallic compounds

The enthalpies of formation of rare earth-3d metal alloys and intermetallic compounds have been calculated by Miedema's semiempirical method. The calculations agree well with experimental enthalpy data and with phase diagram information. A brief comment on Miedema's model is given and the possibility of predicting the enthalpies of formation of multicomponent alloys and intermetallic compounds is discussed.