Chemical Thermodynamics and Thermal Analysis最新文献

In part I of this series we established optimised sum values, for each of the chemical elements, of formula volumes, of absolute entropies, and of constant pressure heat capacities, together with their temperature coefficients. These atom values, when summed for a chemical formula, provided zero-level estimates of the corresponding property of that chemical material. Atom sums have the particular advantage of being essentially complete because of the finite number of chemical elements and are of use in prediction and checking of values for chemical materials. However, this is at the expense of an inability to distinguish among isomers and phases with the same chemical formula nor do they allow for effects of atom interactions.

In the present publication, we present optimised atom sums for formation entropies, formation enthalpies and their relation to formation Gibbs energies.

In order to check the reliability of the results, comparison is made among methods of prediction using each of DFT calculations, a proprietary group contribution method, and the proposed single atom sum method. The single atom sum method is found to be most suitable as an initial estimate for large formation entropies and also for large values of formation enthalpies, which includes ionic hydrates.

The energy contributions of the elements group into the Groups of the Periodic Table so that strict atom independence and thus additivity is not predominant while entropy terms are relatively constant (for the non-gaseous elements) implying that the atoms behave independently and thus additively in contributing to the entropy terms resulting from their vibrations within the ionic solids. This is possibly a unique demonstration resulting from this single atom sum collection.

This now comprises a complete set for simple zero-order thermodynamic prediction and for checking, which should be complemented by whatever other resources are available to the researcher.

Physical properties, such as density, (ρ) and refractive index, (n) of three hydroxamic acids (N-phenylbenzo-, N-phenyl-4-methyl-3-nitrobenzo-, and N-phenyl-4-nitrobenzo-) were measured in dimethyl sulfoxide (DMSO) as a function of concentrations at T = (298.15, 303.15, 308.15, and 313.15) K . The apparent molar volumes ($V_{\varphi }^0$), limiting apparent molar volumes ($V_{\varphi }^0$) at infinite dilution, slope ($S_V^{*}$) and Hepler's constant (${\partial }^2{V}_{\varphi }^0\partial T^2$) are calculated from the experimental values of densities (ρ) by applying the Masson's equation. The apparent molar expansibilities at infinite dilution (${{\varphi }^0}_E$), molar volumes (V), thermal expansion coefficient (α₂) and the excess molar volumes (V^E) are also computed. The precise refractive indices (n) data have been used to evaluate the steric parameters viz. molar refractions (R_M), polarizability (α) and excess molar refraction ($R_M^E$) of these molecules. It is inferred from these results that the above mentioned drugs act as structure-making compound due to hydrophobic hydration of the molecules in the drug.

Epoxidation-esterification of fatty acid methyl ester obtained from Anacardium occidentale kernel oil (AOKO), its characterization, kinetics and thermodynamics were the main focus of this study. The methyl ester obtained via base catalyzed transesterification was used for epoxidation-esterification modification process. Epoxidation kinetics and thermodynamics constants were also investigated. The properties of the AOKO and epoxidized-esterified Anacardium occidentale kernel oil (AOKO) methyl ester (MAOKO^e) were determined using standard methods. Rate constant k for the epoxidation process was found to be in the range 4.15 ×${10}^{-5}$Lmol⁻¹s⁻¹ to 19.7 ×${10}^{-5}$Lmol⁻¹s⁻¹; while the activation energy Ea was 35.69 kJ/mol. ΔG, ΔH, and ΔS values for the epoxidation process were (131.59 to 144.40 kJ mol⁻¹), 32.97 kJ mol⁻¹, and $--$320.20 J mol⁻¹ K⁻¹, respectively, indicating non-spontaneous, endothermic, and endergonic nature of the process. The physicochemical characteristics of MAOKO^e were: 2 °C, 293 °C, 815 Kg/dm³, 7.54 mm²/s, 0.78 mgKOH/g, 0.92 mg/Kg and 42.23 KV, for pour point, flash point, density, viscosity, acid value, moisture content and dielectric strength, respectively. The MAOKO^e properties indicated its potential for use as bio-transformer fluid.

The aqueous chemistry of rhenium is of importance for the hydrometallurgical processes involving rhenium alloys, for the leaching of rhenium from its ores and alloys, and for the electrochemical deposition of thin rhenium films. This study aims to present the chemical and electrochemical equilibria in the Re – H₂O system in the form of the Pourbaix diagram. The existing variants of the Pourbaix diagrams for rhenium available in the literature were reviewed; it was shown that they significantly differ from each other in the composition and the values of the thermodynamic activities of rhenium species. The thermodynamic properties of aqueous rhenium species, including the standard Gibbs energies of formation and the standard electrode potentials of half-cell reactions involving it, were collected and analysed. The compounds of rhenium (+7) and rhenium (+6) not isolated in the free aqueous state, and rhenium hydride compounds were discussed. The self-consisted set of thermodynamic data for further calculations was obtained. Using these data, the basic chemical and electrochemical equilibria involving aqueous rhenium species at the temperature of 298 K and the air pressure of 1 bar were calculated. For the first time the potential – pH diagram for the Re – H₂O system at the temperature of 298 K, the air pressure of 1 bar and the different activities of rhenium species in the solution were constructed. The influence of thermodynamic activities of aqueous rhenium compounds on the stability of rhenium oxides was discussed. It was shown that rhenium trioxide ReO₃ is thermodynamically stable only in concentrated solutions (at the activities of rhenium species not less than 10^–6 М), rhenium dioxide ReO₂ loses the stability at the activities of rhenium species less than 10^–8 М, and rhenium sesquioxide Re₂O₃ does so at the activities of rhenium species not less than 10^–14 М. The necessity of the measurement of the stability constants of ortho- and mesorhenate anions, as well as nonahydridorhenates for a deeper understanding of the aqueous rhenium chemistry was discussed.

The low-temperature dynamics and transport of a real gas He, in confined condition are studied employing molecular dynamics simulations. Characterization of the gaseous properties at varying temperatures ($T$) in the range 30 - 150 K, is carried out employing velocity autocorrelation function (VACF), mean squared displacement (MSD), and the transport properties such as, self-diffusion coefficient ($D$) and thermal conductivity ($\lambda$) are determined. In the confined system, gas-wall interactions are found to dictate the above properties, and near-wall accumulation of molecules is observed. Further, depending upon $T$, the effect of wall-mediated forces is found on the distant gas particles. At very short timescales ($t^{*}$ < 0.1), gas-wall interactions result in faster decay of VACF and shorter ballistic phase in MSD along the confining direction, which are most prominent at higher $T$, compared to those for the unconfined directions. Whereas, at short timescales ($t^{*}\sim$ 0.5) non-thermal gas-wall collisions are observed, leading to a minimum in VACF along the confining direction depending upon $T$. At longer timescales ($t^{*}$ > 1), gas-wall particle collisions lead to the sub-diffusive behavior of the confined gas along the confinement, which is most prominent at higher $T$. The results are compared with those for the bulk He to quantify the confining effect on the gas. Reasonably good agreement of the bulk transport properties with numerically calculated quantum mechanical results for LJ potential and existing results from literature (experimental and quantum mechanical) has been found. In the confined system, the parallel self-diffusion coefficient and thermal conductivity ($D_{\parallel }$ and ${\lambda }_{\parallel }$) are found to be close to the bulk values. Additionally, $\lambda$ is estimated from direct heat flux measurements using the Green-Kubo (G-K) formalism and non-equilibrium method for the confined system, and the results are compared. The findings of this work have far-reaching consequences in investigating complex systems.

Density $\left(\rho \right)$ and speed of sound $\left(u\right)$ values of L-Citrulline in aqueous solution, 0.06 mol·kg⁻¹ aqueous Urea and aqueous 0.06 mol·kg⁻¹ Dextrose solutions have been measured at T = (288.15, 293.15, 298.15, 303.15, 308.15, 313.15 and 318.15) K within the concentration range of (0.02 to 0.2) mol·kg⁻¹.These measurements have been performed to evaluate some important parameters, viz, apparent molar volume of solute $\left(V_{\varphi }\right)$, limiting apparent molar volume of solute $\left(V_{\varphi }^0\right)$, limiting apparent molar volume of transfer $\left({\Delta }_{tr}{V}_{\varphi }^0\right)$, limiting apparent molar expansivity$\left(E_{\varphi }^0\right)$, thermal expansion coefficient (${\alpha }^{*}$), Hepler's constant $\left(\frac{{\partial }^2{V}_{\varphi }^0}{\partial T^2}\right)$, isentropic compressibility (${\kappa }_s$), apparent molar compressibility $\left(K_{s,\varphi }\right)$, limiting apparent molar compressibility $\left(K_{s,\varphi }^0\right)$, limiting apparent molar isentropic compressibility of transfer $\left({\Delta }_{tr}{K}_{s,\varphi }^0\right)$and hydration number$\left({\eta }_H\right)$ . The results have been interpreted in terms of different interactions taking place in aqueous solutions.

Differential scanning calorimetry has been used to measure the enthalpy of formation for manganese, iron, cobalt, nickel, copper and zinc oxalate. By adding a flameless combustion catalyst (CuO) and using scans of 2 K min⁻¹ in static air, the values determined for each compound agreed to within 1% of the critically reviewed values reported previously. Confident in the approach's validity, values for metal oxalates that did not have accepted values in the compilation are also presented. This approach has the potential to measure reliable Δ_fH values for any compound where the products can be fully oxidized during the decomposition.

Recently, the treatment of waste water by Zr-based adsorbents had significantly attracted wide interest among researchers owing to its distinct features. The unique properties of Zr such as thermal stability, large size, high positive charge, greater mechanical rigidity and acid-base nature are mainly responsible for its diverse application. In this work, designing of the new adsorbent material containing tetravalent Zr metal oxide layered double hydroxide (LDH) composite for the removal of anionic dye was studied. The modification of LDH was conducted via the urea hydrolysis method by using zirconium salts as a precursor material. The adsorption efficiency of the as-synthesized material represented as ZrO₂/MgAl-LDH was investigated for the decontamination of congo red (CR) dye from an aqueous medium. The adsorbent ZrO₂/MgAl-LDH composite was characterized by several instrumental techniques including powder X-ray diffraction (P-XRD), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy(FT-Ir), scanning emission microscopy(SEM), energy dispersive X-ray(EDX), transmission emission microscopy(TEM) and thermogravimetric analysis(TGA). The influence of several experimental factors on the adsorption equilibrium studies such as pH, temperature, initial dye concentration, contact time, adsorbent dosages, and interfering ions are examined under optimized conditions. The thermodynamic study manifests the spontaneous and endothermic nature of the sorption process. Additionally, based on fitting the experimental data with different models the isotherm and kinetics mechanism are found to be more appropriate with Langmuir isotherm, Redlich-Peterson isotherm, and pseudo-second-order kinetics. The spectral analysis further indicates the oxidizing nature of the material, therefore favoring the adsorption of anionic dye. The maximum dye removal efficiency of ZrO₂/MgAl-LDH reached up to 97.19% under the optimum reaction condition (initial dye concentration = 50 mg/L, contact dosages = 0.02 g, temperature = 303 K). In addition, the maximum monolayer adsorption capacity (q_max= 169.42 mg) for CR adsorption also reveals its superiority in adsorption test. Moreover, the adsorbent can be easily retrieved and reused up to fifth cycle. Therefore, the characterization and experimental results of ZrO₂/MgAl-LDH affirms its potential application for effective decontamination of waste water.

The critical volume$V_c$, the relation between the critical temperature and the pressure T_c / P_c and the product $P_c{V}_c^2$ depend linearly on the number of carbons in a homologous series as a consequence of the theory of corresponding states. This suggests that additive and constitutive properties are suitable for the construction of equations of state. In this article, an equation of state of Soave–Redlich–Kwong type is proposed: an additive and constitutive equation of state because it contains among its constitutive parameters the parachor $\left({\wp }_{ch}\right)$ and the molar refraction $\left(R_m\right)$. The homologous series of the n-alkanes is used to illustrate the applicability of the proposed equation.

Water is a fascinating substance with lots of properties not encountered in other compounds. It has been suggested that making use of water's “anomalous” properties can lead to exciting applications in various disciplines e.g. engineering, medicine and physiology. The origin of these anomalous properties is far from clear, with the strong hydrogen bonds of water being only part of the answer. Moreover, water's structure and dynamics are not entirely understood either and new theories have appeared and debated during the 21st century. This review, aiming at a broader/general audience, attempts to review briefly some research trends related to water's structure, properties and applications. New experimental results for the debated phenomena of water bridge and exclusion zone are also presented and discussed. Various explanatory mechanisms for the exclusion zone are reviewed and a new proposal is put forward. A –hopefully- unbiased discussion is presented for both “mainstream” and unconventional theories and trends and future directions are also outlined.