Molar Internal Energy Research Articles

CONTROL OF PARAMETERS AND STRUCTURE OF DETONATION WAVE IN A DUAL-FUEL METHANE-HYDROGEN MIXTURE

A generalized model of chemical kinetics of detonation combustion of stoichiometric dual-fuel methane-hydrogen mixture is proposed. It allows calculating the molar mass and internal energy of a mixture without calculating its detailed chemical composition. The model was verified within the framework of a numerical calculation of the cellular multifront structure of a detonation wave. The calculated size of the detonation cell, as well as the qualitative structure of detonation (irregularity of the cellular structure due to the formation of both primary and secondary transverse waves, and incomplete combustion of gas in the detonation wave) are in good agreement with experiment.

Thermodynamics of mixtures containing a fluorinated benzene and a hydrocarbon

Fluorobenzene, or 1,4-difluorobenzene or hexafluorobenzene + alkane mixtures and hexafluorobenzene + benzene, or + toluene, or + 1,4-dimethylbenzene systems have been investigated using thermodynamic properties from the literature and through the application of the DISQUAC and UNIFAC (Dortmund) models and the concentration-concentration structure factor (SCC(0)) formalism. DISQUAC interaction parameters for the contacts F/alkane and F/aromatic have been determined. UNIFAC interaction parameters available in the literature for these contacts have been used along calculations. Both models predict double azeotropy for the C6F6 + C6H6 system, although in different temperature ranges. TheHmE values of the fluorobenzene, or 1,4-difluorobenzene + n-alkane systems are positive and are accurately described by the models using interaction parameters independent of the n-alkane. This means that no Patterson’s effect exists in such mixtures. DISQUAC calculations allow state that such conclusion is still valid for C6F6 + n-alkane mixtures. DISQUAC provides better results than UNIFAC on CpmE of solutions involving n-alkanes, or on HmE of C6F6 + aromatic hydrocarbon systems. Mixtures with alkanes are characterized by interactions between like molecules, which are mainly of dispersive type, which is supported, e.g, by the negative CpmE values of these systems. It is shown that structural effects can contribute largely to HmE. This is investigated in terms of the excess molar internal energy at constant volume, UVmE, whose values are determined for the investigated solutions. For mixtures with a given n-alkane, the relative variation of HmE and UVmEwith the fluorohydrocarbons is different.HmEvalues change in the sequence C6F6 > 1,4-C6H4F2 > C6H6 > C6H5F, while UVmE changes in the order: 1,4-C6H4F2 > C6H6≈ C6H5F > C6F6 . C6F6 + aromatic hydrocarbon mixtures are characterized by interactions between unlike molecules as it is demonstrated by their negative HmE values. The application of the SCC(0) formalism reveals that homocoordination is more important in C6F6 + n-alkane mixtures than in the corresponding systems with C6H5F, and that heterocoordination is dominant in the solutions of C6F6 with an aromatic hydrocarbon.

Thermodynamics of mixtures with strong negative deviations from Raoult’s law. XVIII: Excess molar enthalpies for the (1-alkanol + cyclohexylamine) systems at 298.15 K and modelling

Excess molar enthalpies, HmE, have been measured using a Tian-Calvet microcalorimeter for the systems CH3(CH2)u-1OH (u = 1,2,3,4,7,10) + cyclohexylamine at 298.15 K and 0.1 MPa. The HmE values are large and negative, indicating the existence of strong interactions between unlike molecules, which is consistent with the also large and negative excess molar volumes, VmE of these solutions, previously measured by us. The contribution from the equation of state term to HmE has been evaluated for the 1-alkanol + cyclohexylamine, or + 1-hexylamine, or + aniline mixtures, and the corresponding excess molar internal energies at constant volumes, Um,VE, determined. It is shown that such contribution is particularly important for the methanol + aniline system, in such way that the excess functions HmE and Um,VE have different sign at x1 = 0.5. The DISQUAC and ERAS models have been applied to the cyclohexylamine systems, and the interaction parameters reported. DISQUAC improves ERAS results on HmE. The latter model describes correctly the VmE curves. The variation of HmE of CH3(CH2)u-1OH + cyclohexylamine, or + 1-hexylamine, or + aniline mixtures with u along a homologous series with a given amine, or with the amine in mixtures with a given 1-alkanol is discussed in terms of the different interactional contributions to HmE.

Density, speed of sound, refractive index and relative permittivity of methanol, propan-1-ol or pentan-1-ol + aniline liquid mixtures. Application of the Kirkwood-Fröhlich model

Densities (ρ) and speeds of sound (c) at a temperature T = 298.15 K, relative permittivities at 1 MHz (εr) and refractive indices at the sodium D-line (nD) at T = (293.15 K to 303.15 K), all of them at a pressure p = 0.1 MPa, are reported for binary liquid mixtures alkan-1-ol + aniline. The alkan-1-ols considered are methanol, propan-1-ol and pentan-1-ol. Also, the values of the excess molar volume (VmE), excess isentropic compressibility (κSE), excess speed of sound (cE), excess refractive index (nDE), excess relative permittivity (εrE) and its temperature derivative (∂εrE/∂T)p are calculated and fitted to Redlich-Kister polynomials. The agreement among the reported data and other literature sources is analysed by comparing VmE, nDE, εrE and the deviation of c from mole-fraction linearity (Δc). The positive excess molar internal energies at constant volume (Um, VE) show the dominance of the breaking of interactions between like molecules in the energy balance on mixing, particularly the breaking of strong dipolar interactions between aniline molecules. This contribution is also dominant for the εrE values, as they are negative and decrease with the length of the alkan-1-ol chain. Calculations on the concentration-concentration structure factor are consistent with these statements, revealing homocoordination in the studied systems. The VmE are negative, which together with the positive Um, VE indicate the existence of important structural effects in the studied mixtures. The application of the Kirkwood-Fröhlich model shows that the average relative orientation of neighbouring dipoles is similar in the mixtures methanol + aniline or + pyridine, in spite of the different character of the predominant interactions in the latter mixture (heterocoordination).

First principles study of thermodynamic properties of Cd-substituted Zn Chalcogenides by employing quasi harmonic Debye model

First Principles study of thermodynamic properties of Cd-substituted Zn Chalcogenides have been performed by using quasi harmonic Debye Model. A non linear variation in bulk modulus of is found in Chalcogen’s group (X = O, S, Se, Te). Slack equation is used to calculate the thermal conductivity of materials and it is found that Cd-rich Zn Chalcogenides have less thermal conductivity. The anharmonicity and thermal expansion coefficient of increase linearly from X = O to X = Se but then interestingly a crossover is appeared in their values at X = Te. Several other thermodynamic parameters like Debye temperature, molar heat capacities, internal energy and entropy are also determined and compared to available theoretical and experimental results.

Maxwell–Stefan diffusion coefficient model derived from entropy generation minimization principle for binary liquid mixtures

A new model for the Maxwell–Stefan (MS) diffusion coefficient was developed in this study. The entropy generation minimization principle was used to derive the expression of the MS diffusion coefficient, which has a similar form as Eyring’s model. Molar excess internal energy based on two-liquid theory was derived to correct the error induced by the linear mixing rule. The local surface area fraction was used to replace the bulk fraction by considering the intermolecular friction force exerting on the molecular surfaces. The new model was applied to calculate the Fick diffusion coefficients for four binary systems, which were measured experimentally by digital holographic interferometry. Comparison of the experimental and calculation results indicated that the proposed model has a good performance for calculating the diffusion coefficients for the mentioned binary systems.

Quantitative model of super-Arrhenian behavior in glass forming materials

The key feature of glass forming liquids is the super-Arrhenian temperature dependence of the mobility, where the mobility can increase by ten orders of magnitude or more as the temperature is decreased if crystallization does not intervene. A fundamental description of the super-Arrhenian behavior has been developed; specifically, the logarithm of the relaxation time is a linear function of $1/{\overline{U}}_{x}$, where ${\overline{U}}_{x}$ is the independently determined excess molar internal energy and $B$ is a material constant. This one-parameter mobility model quantitatively describes data for 21 glass forming materials, which are all the materials where there are sufficient experimental data for analysis. The effect of pressure on the $loga$ mobility is also described using the same ${\overline{U}}_{x}(T,p)$ function determined from the difference between the liquid and crystalline internal energies. It is also shown that $B$ is well correlated with the heat of fusion. The prediction of the $B/{\overline{U}}_{x}$ model is compared to the Adam and Gibbs $1/T{\overline{S}}_{x}$ model, where the $B/{\overline{U}}_{x}$ model is significantly better in unifying the full complement of mobility data. The implications of the $B/{\overline{U}}_{x}$ model for the development of a fundamental description of glass are discussed.

Size- and shape-dependence of the thermodynamic properties of nanocrystals

The thermodynamic properties, especially the surface thermodynamic properties of nanocrystals (NCs) play important roles in the physicochemical changes involving NCs. However, it remains unclear about the influence regularities of size and shape on the thermodynamic properties of NCs. Thus by introducing interface variables into the Gibbs energy and combining Young-Laplace equation, relations between the thermodynamic properties (molar Gibbs energy, enthalpy, entropy, internal energy and heat capacity), respectively, and size of NCs with different shapes (sphere, cube, rodlike and sheet) were systematically derived. Theoretical estimations of the orders of the surface thermodynamic properties of NCs are in good agreements with available experimental values. Furthermore, the Tolman length and the surface tension were surprisingly obtained based on the calculated results of the surface thermodynamic properties of Al NCs. The influence regularities of size and shape on the thermodynamic properties of the reaction, the melting, the adsorption and the dissolution of NCs are reasonably explicated by the employment of the above thermodynamic relations.

Thermodynamic characteristics up to the melting point and phonon density of states of Al(C11H19O2)3

The work presents results of research on a set of important characteristics of the molecular crystal Al(C11H19O2)3 based on experimental heat capacity data. The heat capacity was measured in the temperature range 299–432 K. The isobaric thermodynamic functions (entropy, enthalpy and reduced Gibbs energy) were calculated. The phonon density of states g(ω) was calculated using high-precision data on low-temperature heat capacity. Using the information about g(ω), the isochoric thermodynamic functions (heat capacity, entropy, internal energy and reduced Helmholtz energy) in the range 0–494 K were calculated. Molar zero-point energy, total enthalpy and internal energy of Al(C11H19O2)3 were determined. The knowledge of zero-point energy is very important when considering the energy balance of the solid and can be used to investigate the stability of the crystal lattice. All obtained characteristics were evaluated for accuracy.

Physicochemical properties of [cnmim][thr] (n = 3, 5, 6) amino acid ionic liquids

A series of ionic liquids based on amino acid, threonine, [Cnmim][Thr] (n=3, 5, 6) (1-alkyl-3-methylimidazolium threonine salt), was designed and synthesized. The density, surface tension and refractive index were measured over the range of T=(288.15–328.15)K and the atmospheric pressure. The molar surface Gibbs energy, g, have been calculated. Using the molar surface Gibbs energy, a new Eötvös equation was obtained in which each parameter has a clear physical meaning. In terms of the thermodynamic relationship, the molar surface entropy, s, enthalpy, h, and the ratio of molar surface internal energy to molar internal energy of vaporization, Er were calculated and the molar entropy of vaporization of surface, ΔSvs was estimated. For [Cnmim][Thr] and other ILs, low values of s and high values for ΔSvs, and low values for Erψ were obtained and these data indicate the surface layer of the ILs is almost the same as that of the bulk liquid, except for a few neighbours in the direction of the gas phase. From the refractive index and the molar surface Gibbs energy, an equation to predict the surface tension of ILs was derived and the predicted values were highly correlated with the corresponding experimental ones.

Influence of different micro-vibrational behavior on the thermodynamic properties of SO gas

The effects of different micro-vibrational motions of sulfur oxide on its thermodynamic properties have been carried out. The theoretical full set of vibrational levels {Eυ} and the maximum vibrational quantum number υmax of the ground electronic state X3Σ− of SO molecule are obtained using the variational algebraic method (VAM) for vibrational motions. In the temperature range of 300–4000K, the molar internal energies, the molar entropy and the vibrational heat capacities are studied by implementing the VAM vibrational energies to the classical statistical thermodynamic formulae. Compared with credible experimental data, the VAM thermodynamic results are better consistent with the experiment than the traditional simple harmonic oscillator (SHO) model and the configuration interaction (CI) calculations.

Refinement of the theoretical solubility model and prediction of solute solubility in mixed solvent systems

We have refined the non-polar (van der Waalls) and hydrogen bonding interaction term of STMIPE-AC (statistical thermodynamic molar intermolecular potential energy activity coefficient) model, which reduces the average error of the model in correlating the molar internal energy change on vaporization of pure liquids (62 solvents, 10 temperature points for each solvent) from 6.6% to 3.1%. The binary interaction parameters kij are fitted to the solubility data of solid solutes in pure solvents or estimated from a semi-empirical equation using a similar local composition method, and then they are used to predict the solute solubility in mixed solvents. The overall average relative error (ARE) in predicted solubility (15 solutes, 64 systems, 1091 data points) is 11.24%, which makes this model a practical approach for crystallization process development.

Hildebrand Solubility Parameters of Amidium Ionic Liquids

The Hildebrand solubility parameters of amidium ionic liquids were investigated using the approach of intrinsic viscosity. It was discovered that the nature of the anion influences the Hildebrand solubility parameters by which distillable trifluoromethanesulfonate- (TfO-) based ionic liquids present higher Hildebrand solubility parameters than bis(trifluoromethylsulfonyl)imide- (NTf2-) based ionic liquids. In this work, we also studied the effect of dissolution temperature on the Hildebrand solubility parameters of ionic liquids. An increase in temperature from 25 to 60 °C results in a decrease in the Hildebrand solubility parameters of ionic liquids. Moreover, the cohesive energy density, molar internal energy, and enthalpy of dissolution were evaluated. The molar internal energy and enthalpy of dissolution are almost constant or show a slight decrease with increasing dissolution temperature for O-methylated TfO-based ionic liquids.

Molecular Dynamics and ab Initio Studies of the Effects of Substituent Groups on the Thermodynamic Properties and Structure of Four Selected Imidazolium-Based [Tf2N–] Ionic Liquids

All-atom molecular dynamics simulations combined with ab initio calculations are used to study the thermodynamic properties and microscopic structure of four ionic liquids (ILs) based on the imidazolium cation with different alkyl side branches, ([bmmim]+, 1-butyl-2,3-dimethylimidazolium; [bmim]+, 1-butyl-3-methylimidazolium; [apmim]+, 1-(3-aminopropyl)-3-methylimidazolium; [mim]+, 1-methylimidazolium), paired with the [(CF3SO2)2N]−, bis(trifluoromethanesulfonyl)imide anion, in the temperature range of (298 to 600) K. We observed the highest value of the molar internal energy, enthalpy of vaporization, and cohesive energy density for the amine-functionalized [apmim][Tf2N] ionic liquid. Structural analysis shows that the amine functionalization of the end of the alkyl side chain of imidazolium cation does not significantly affect the organization of [Tf2N]− around [apmim]+, but additional NH2 groups lead to short-range cation–cation structural correlations between neighboring [apmim]+. The C2 methylation e...

Thermodynamics of organic molecule adsorption on sorbents modified with 5-hydroxy-6-methyluracil by inverse gas chromatography

The thermodynamic features of organic molecule adsorption from the gaseous phase of sorbents modified with 5-hydroxy-6-methyluracil (HMU) were studied. Molar internal energy and entropy of adsorption variation analyses showed that with every type surface, except for silica gel, layers of supramolecular structure have cavities equal in size with the ones revealed in HMU crystals by X-ray diffraction. Adsorption thermodynamics on HMU-modified sorbents depended on the amount of impregnated HMU and on the polarity, but not the porosity, of the initial sorbent. Polarity of the modified surface increased as a function of HMU quantity and initial sorbent mean pore size, but become appreciably lower if the initial surface is capable of hydrogen bonding.

Effect of different molecular vibrational models on thermodynamic properties

The full set of vibrational energies {Eυ} and the maximum vibrational quantum number υmax generated by an algebraic method (AM) are suggested to implement classical statistical thermodynamic formulae. This protocol is applied to study the molar vibrational internal energy, molar vibrational entropy and molar vibrational heat capacity of a macro-system consisting of the ground electronic state X1Σ+ of CO molecules. Comparisons of theoretical results with experimental measurements show that the AM statistical thermodynamic quantities are much better than those generated using beautiful analytical formulae that are based on the traditional simple harmonic oscillator (SHO) vibrational model, and that the suggested protocol can be extended to study statistical thermodynamic properties of any macro-diatomic system.

Thermodynamics of ketone + amine mixtures. Part X. Excess molar enthalpies at 298.15 K for N,N,N-triethylamine + 2-alkanone systems. Characterization of tertiary amine + 2-alkanone, and of amino-ketone + n-alkane mixtures in terms of DISQUAC

Molar excess enthalpies, HmE, at 298.15K and 0.1MPa have been measured using a Tian–Calvet microcalorimeter for N,N,N-triethylamine (TEA)+2-alkanone mixtures. These data have been used to determine ΔHN-CO, the enthalpy of the amine-ketone interaction, which is practically independent of the ketone size. This allows explain the observed HmE decrease when the ketone size is increased in terms of a lower positive contribution to HmE from the breaking of the alkanone-alkanone interactions. Inspection of molar excess volumes and of molar excess internal energies at constant volume (determined in this work) reveals the existence of structural effects, which are more important for mixtures with 2-heptanone. Tertiary alkyl amine+2-alkanone, and amino-ketone+n-alkane mixtures have been treated in terms of DISQUAC. The interaction parameters for the carbonyl/amine contacts are reported. It is shown that such contacts are essentially dispersive. Proximity effects in amino-ketone mixtures lead to increased dispersive parameters in comparison to those of amine+ketone solutions. Steric effects related to the length of the alkyl chains attached to the N atom lead to decreased dispersive parameters. DISQUAC describes accurately vapour–liquid equilibria (VLE) and HmE of the investigated mixtures, which have been also treated using UNIFAC (Dortmund version). UNIFAC predictions compare well with DISQUAC results for TEA mixtures. For amino-ketone systems, UNIFAC calculations largely differ from the experimental results. This reveals that interactions parameters must be modified to take into account proximity effects.

Thermodynamics of ketone + amine mixtures. Part IX. Excess molar enthalpies at 298.15 K for dipropylamine, or dibutylamine + 2-alkanone systems and modeling of linear or aromatic amine + 2-alkanone mixtures in terms of DISQUAC and ERAS

Excess molar enthalpies, HmE, at 298.15K and atmospheric pressure, have been measured, over the entire mole fraction range, by means of a Tian–Calvet microcalorimeter, for the systems: dipropylamine (DPA), or dibutylamine (DBA)+2-propanone,+2-butanone,+2-pentanone, or+2-heptanone. These data, together with those available in the literature for aniline or N-methylaniline+2-alkanone systems, or for 2-alkanone, or amine+heptane mixtures have been used to determine ΔHNCO, the enthalpy of the amine–ketone interactions. For solutions with a given aromatic amine, ΔHNCO values are large and decrease with the increasing of the ketone size. The corresponding HmE values are large and negative. Mixtures with DPA or DBA are characterized by much weaker interactions between unlike molecules and ΔHNCO is nearly independent of the ketone. The HmE values are positive and decrease when the chain length of the 2-alkanone is increased, which has been ascribed to a decreasing positive contribution to HmE from the disruption of the ketone–ketone interactions upon mixing. Excess molar internal energies at constant volume, UVmE, have been obtained from HmE data using our previous volumetric measurements for the studied mixtures. Similar trends that for HmE are observed. Differences between UVmE and HmE are about 15% for DPA or DBA solutions and are ranged between 35% and 45% for mixtures with aromatic amines. The excess molar volume, VmE, changes in line with HmE and both magnitudes are usually of the same sign, which reveals that the main contribution to the former is the interactional one. In systems including linear secondary amines, structural effects increase with the chain length of the ketone. Amine+2-alkanone systems have been also investigated in terms of the DISQUAC, UNIFAC and ERAS models. DISQUAC and ERAS interaction parameters are reported. As in other many applications, the quasichemical interchange coefficients for l=1 (Gibbs energy), 3 (heat capacity) remain constant along each homologous series considered. DISQUAC improves meaningfully ERAS results on HmE, while UNIFAC results are slightly better. This suggests that physical interactions are more relevant than those related to association/solvation effects.

Infinitely Dilute Partial Molar Properties of Peptides and Proteins from Computer Simulation

A detailed understanding of temperature and pressure effects on an infinitely dilute solute's conformational equilibrium requires knowledge of infinitely dilute partial molar properties. Established molecular dynamics methodologies generally have not provided a way to calculate these properties without either a loss of thermodynamic rigor, the introduction of non-unique parameters, or a loss of information about which solute conformations specifically contributed to the output values. Here we describe a method that is simple in execution and possesses none of the above disadvantages. We use it to calculate the infinitely dilute partial molar internal and kinetic energies, enthalpy, volume, isothermal compressibility, heat capacity, and thermal expansion coefficient for two proteins, pancreatic trypsin inhibitor and lysozyme. Further, we test the method's performance, in light of currently accessible simulation timescales, to precisely distinguish the thermodynamic differences between a native and denatured conformation of the trp-cage miniprotein. We conclude that those properties corresponding to fluctuating quantities (e.g., partial molar compressibility, thermal expansion coefficient, and heat capacity) will be computationally demanding to calculate precisely, but the other properties (e.g., partial molar volume and enthalpy) can be calculated with the computational power widely available to the community today. The ability to assign properties to specific conformations is a major advantage of our approach.

Hildebrand solubility parameters of ionic liquids: Effects of ionic liquid type, temperature and DMA fraction in ionic liquid

The Hildebrand solubility parameters of 10 ionic liquids were investigated using the approach of intrinsic viscosity. Effects of dimethylacetamide (DMA) fraction in ionic liquids and dissolution temperature on the Hildebrand solubility parameter were also studied. Moreover, cohesive energy density, molar internal energy and enthalpy of dissolution were calculated. Cation and anion of an ionic liquid shows a significant influence on the solubility parameter. The values of ionic liquids containing BMIM cations are in the following order: [PF6]>[Tf2N]>[Cl], while those of ionic liquids containing EMIM cations are in the order: [BF4]>[DEPO4]>[AC]. Ionic liquid containing HOEMIM exerts the highest solubility parameter than that containing MBPYRRO or BMIM. Considering effect of varying DMA fraction, the Hildebrand solubility parameters of the mixtures do not correspond to the mixing rule. Their values tend to be closer to those of the ionic liquids than that of DMA for 40–90vol% DMA added in the ionic liquids (1-Ethyl-3-methylimidazolium acetate (EMIM-AC) and 1-Butyl-3-methylimidazolium chloride (BMIM-Cl)). With increasing temperature from 25 to 60°C, decreases of Hildebrand solubility parameters from 25.2 to 24.7 for EMIM-AC and the mixture of EMIM-AC/DMA (60–40v/v) were obtained. The cohesive energy densities of ionic liquids at the different conditions are proportional directly with the Hildebrand solubility parameter. The molar internal energy and the enthalpy of dissolution decrease with increasing DMA fraction in ionic liquids, while they are almost constant or show slight decreases with the increase of dissolution temperature for EMIM-AC and the mixture of EMIM-AC/DMA (60–40v/v), respectively.