Showing papers on "Standard molar entropy published in 2019"

Thermodynamic Properties of Gaseous Carbon Disulfide.

Abstract: Efficient analytical representations of the thermodynamic properties for carbon disulfide remain open challenges in the communality of science and engineering. We present two analytical representations of the entropy and Gibbs free energy for gaseous carbon disulfide which we find to be of satisfactory accuracy and convenient for future use. The proposed two analytical representations merely rely on five molecular constants of the carbon disulfide molecule and avoid applications of a large number of experimental spectroscopy data. In the temperature range from 300 to 6000 K, the average relative deviations of the predicted molar entropy and reduced Gibbs free energy values from the National Institute of Standards and Technology database are 0.250 and 0.108%, respectively.

Stoichiometric, Thermodynamic and Computational DFT Analysis of Charge Transfer Complex of 1-Benzoylpiperazine with 2, 3-Dichloro-5, 6-Dicyano-1, 4-benzoquinone

Abstract: This research discusses the charge transfer (CT) complex of 1-benzoylpiperazine (1-BP) as a donor with the π-acceptor of 2, 3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) which has been studied spectrophotometrically in acetonitrile (ACN) at different temperatures. The 1:1 molecular composition of the CT complex was confirmed by applying Job’s continuous variation and photometric titration methods and the Benesi–Hildebrand equation is used to calculate the formation constant (KCT) and molar extinction coefficient (e). The thermodynamic parameters standard enthalpy (ΔH°), standard entropy (ΔS°) and standard Gibbs energy (ΔG°) were calculated by using van’t Hoff equation. These results indicate that the CT complex formation is exothermic. The computational study of the CT complex, using density functional theory, supports the experimental work. The molecular geometry, molecular electrostatic potential maps, characterization of the frontier molecular orbital surfaces, Mulliken partial atomic charges and reactive parameters of the acceptor and donor are helpful in assigning the CT route. The charge transfer in the 1-BP–DDQ complex and its high stability are evidenced through both experimental and theoretical studies.

Heat capacity measurement of C14–ZrMn2 and thermodynamic re-assessment of the Mn–Zr system

Abstract: The CALPHAD approach was used to derive thermodynamic parameters of the Mn–Zr system based on experimental results and critical evaluation of available data. Novel ab-initio calculations as well as experimental data on enthalpy of formation and heat capacity measurements for the C14–ZrMn2 Laves phase were taken into account. The congruent melting point of the C14–ZrMn2 Laves phase was determined using differential thermal analysis (DTA) at 1765 K. Data on heat capacity for the C14–ZrMn2 phase were extended to high temperature range up to 980 K using differential scanning calorimetry (DSC). Standard entropy for C14–ZrMn2 was calculated using an extended Einstein model based on newly obtained results. Additionally, the sublattice model based on antisite substitution in the C14–ZrMn2 Laves phase has been used in order to describe its homogeneity range. Based on the currently obtained results and novel literature data, thermodynamic parameters for the Mn–Zr system were re-optimized. The self-consistent thermodynamic description derived in the present work reproduces all experimental data well.

Predictions of Entropy and Gibbs Energy for Carbonyl Sulfide.

Abstract: Many chemical and physical equilibrium conditions can be determined from minimizing the Gibbs free energies of the system. Efficient analytical representations of the entropy and Gibbs free energy of carbonyl sulfide remain elusive in the communality of science and engineering. Here, we report two analytical representations of the entropy and Gibbs free energy for carbonyl sulfide, and the prediction procedures only involve six molecular constants of the carbonyl sulfide molecule. In the temperature range from 300 to 6000 K, the average relative deviations of the predicted molar entropy and reduced Gibbs free energy values of carbonyl sulfide from the National Institute of Standards and Technology database are arrived at 0.150 and 0.189%, respectively.

A Simple Semiempirical Method for Predicting the Temperature–Entropy Saturation Curve of Pure Fluids

Abstract: In this work we propose an approximate analytical method to obtain the liquid–vapor saturation curve in a Tr–s* diagram, with Tr = T/Tc, s* = (s – sc)/R, Tc the critical temperature, s the molar entropy, sc the critical molar entropy, and R the gas constant, for a given fluid. The method uses a modified rectilinear diameter law for the saturated liquid and vapor entropies and an extended corresponding states equation for the entropy of vaporization. From this method, two approximations are derived. The first approximation requires the use of data obtained from RefProp or a similar program. The second approximation only needs Tc, the critical molar volume, vc, and the acentric factor, ω, of the fluid as input data. For most fluids, both approximations yield very good predictions.

Accurate entropy calculation for large flexible hydrocarbons using a multi-structural 2-dimensional torsion method.

Abstract: Entropy is one of the key thermodynamic parameters in combustion kinetic modeling. Accurate entropy prediction needs to account for the conformational torsional anharmonicity, which could be solved by the state-of-the-art multi-structural torsion (MS-T) method. However, this method is computationally expensive or even not feasible for large flexible molecules. To address this issue, we proposed a multi-structural 2-dimensional torsion (MS-2DT) method that adopts minimally coupled torsions to reduce the computational cost. In this method, a series of 2-dimensional coupled torsion combinations were used to generate an initial conformer space with a size of CN2·9 (N is the number of torsions). The standard entropy (and the heat capacity) values of 18 C6–C8 alkanes with 5–7 torsions were computed at 200–2000 K. The MS-2DT calculation is in good agreement with the benchmark MS-T method: only a small deviation of −0.19 ± 0.15 cal mol−1 K−1 in standard entropy and −0.10 ± 0.21 cal mol−1 K−1 in heat capacity. Additionally, a further application of MS-2DT to n-decane with 9 torsions implies an improved accuracy in entropy (and heat capacity) prediction compared to other conventional simplified treatments. This method provides an affordable and accurate solution to treat the conformational torsional anharmonicity of large flexible alkanes.

Thermal analysis of structural phase transition behavior of Ln 2 Ni 1−x Cu x O 4+δ (Ln = Nd, Pr) under various oxygen partial pressures

Abstract: Structural phase transition behavior between orthorhombic and tetragonal in Ln2Ni1−xCuxO4+δ (Ln = Nd, Pr), which attracts interest as new cathode material for solid oxide fuel cells, has been investigated with thermal analysis under controlled oxygen partial pressures (P(O2)). For Nd2Ni1−xCuxO4+δ with 0.0 ≤ x ≤ 0.1, temperature, enthalpy change (ΔH) and change in excess oxygen content (Δδ) at the phase transition decreased with increasing Cu content. The phase transition temperature decreased with decreasing P(O2), whereas little variation was observed in ΔH and Δδ. For Nd2Ni1−xCuxO4+δ with x ≥ 0.15, crystal structure was tetragonal and no phase transition was detected below 750 °C. For Pr2Ni1−xCuxO4+δ with x = 0.0 and 0.1, phase transition was observed by DSC, showing similar dependence of phase transition temperature and ΔH on Cu content and P(O2) with that of Nd2Ni1−xCuxO4+δ. Δδ was not detected in TG curve of Pr2Ni0.9Cu0.1O4+δ, which could be attributed to too small Δδ. From Ellingham diagram prepared using temperature and P(O2) at the phase transition, variation of standard enthalpy (ΔH°) and standard entropy (ΔS°) was evaluated. It was revealed that variation of phase transition temperature by Cu content and difference of the phase transition temperature between Nd2Ni1−xCuxO4+δ and Pr2Ni1−xCuxO4+δ showed correspondence with variation of ΔH°. Excess oxygen content, δ, in Nd2Ni1−xCuxO4+δ, evaluated with reduction in TG apparatus, decreased with increasing Cu content. It was suggested that some amount of δ was required for stabilization of orthorhombic phase and that low δ by Cu substitution stabilized the tetragonal structure of the specimens with x ≥ 0.15.

Kinetics and Thermodynamics of Adsorption of Rhodamine B onto Bentonite Supported Nanoscale Zerovalent Iron Nanocomposite

Abstract: Bentonite clay supported nanoscale zerovalent iron (BC-nZVI) composite was successfully prepared. BC-nZVI was characterized by physicochemical and spectroscopic techniques. Surface area as determined by sear's method is 291.2 cm2. Adsorption operational parameters were investigated in a batch technique. At 500 mg/L initial concentration, 120 minutes contact time and pH 3, 454.81 mg/g quantity was adsorbed. The highest adsorption percentage removal efficiency was obtained at room temperature. Kinetic data fitted best to pseudo second order and the mechanism was diffusion governed. The kinetic models were further validated by sum of square error (SSE) and non-linear Chi-square statistical models (X2). The values of the thermodynamic parameters: standard enthalpy change ΔH (-10.597 Jmol−1)to (-5558 Jmol−1.), standard entropy change, ΔS (-277.804 J mol−1 K−1)- to (-139.2595 J mol−1K−1) and the Gibbs free energy (ΔG) revealed that the adsorption process was feasible, spontaneous and exothermic in nature. The performance of BC-nZVI enlisted it as a great potential adsorbent for effective removal of Rhodamine B and therefore recommended for application in industrial effluent treatment.

Investigation on the dissolution behavior of 2HNIW·HMX co-crystal prepared by a solvent/non-solvent method in N,N-dimethylformamide at T = (298.15–318.15) K

Abstract: 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexazisowurtzitane (HNIW)·1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) co-crystal in a 2:1 molar ratio was prepared by a solvent/non-solvent method, and the co-crystal has been characterized by several methods. The enthalpies of dissolution of 2HNIW·HMX co-crystal in N,N-dimethylformamide at different temperatures were measured by a DC08-1 Calvet microcalorimeter under standard atmospheric pressure, and it is indicated that the dissolutions are exothermic process. The empirical formulae for the calculation of the molar enthalpy ( $$\Delta_{\text{diss}} H$$ ) of dissolution, relative partial molar enthalpy ( $$\Delta_{\text{diss}} H_{\text{partial}}$$ ), relative apparent molar enthalpy ( $$\Delta_{\text{diss}} H_{\text{apparent}}$$ ), and enthalpy of dilution ( $$\Delta_{\text{dil}} H_{1,2}$$ ) at 298.15 K are obtained. The differential enthalpies ( $$\Delta_{\text{dif}} H$$ ) and kinetic equations describing the dissolution process at different temperatures are deduced. Furthermore, the apparent activation energy E = 10.54 ± 0.22 kJ mol-1 and pre-exponential constant A = 0.34 ± 0.03 s−1 of 2HNIW·HMX co-crystal are obtained. The standard molar Gibbs free energy of activation ( $$\Delta G_{ e }^{\theta }$$ ) at different temperatures is 86.44 ± 0.02 kJ mol−1 (298.15 K), 88.02 ± 0.03 kJ mol−1 (303.15 K), 89.61 ± 0.01 kJ mol−1 (308.15 K), 91.18 ± 0.01 kJ mol−1 (313.15 K), and 92.75 ± 0.02 kJ mol−1 (318.15 K), respectively. The standard molar entropy of activation ( $$\Delta S_{ e }^{\theta }$$ ) and standard molar enthalpy of activation ( $$\Delta H_{ e }^{\theta }$$ ) are − 262.55 ± 0.72 J mol−1 K−1 and 7.98 ± 0.22 kJ mol−1, respectively.

Calorimetric study of siloxane dendrimer of the third generation with trimethylsilyl terminal groups

Abstract: The molar heat capacity of siloxane dendrimer of the third generation with trimethylsilyl terminal groups G3[OSi(CH3)3]24 was determined by precise adiabatic calorimetry and differential scanning calorimetry over the temperature range T = (6–570) K for the first time. The low-temperature structural anomaly and the glass transition were observed in the above temperature range, and the standard thermodynamic characteristics of the revealed transformations were determined and analyzed. The fundamental thermodynamic functions such as the enthalpy [H°(T) − H°(0)], the entropy [S°(T) − S°(0)], and the Gibbs energy [G°(T) − H°(0)] were calculated for the range from T → 0 to 570 K based on the experimentally determined molar heat capacity of the investigated compound. The standard entropy of formation ΔfS° of dendrimer G3[OSi(CH3)3]24 was evaluated at T = 298.15 K. The thermal stability of the studied compound was investigated by thermogravimetric analysis. The standard thermodynamic properties of siloxane dendrimer G3[OSi(CH3)3]24 were compared and discussed with the previously reported data for the studied G3 carbosilane dendrimers with different functional terminal groups on the surface layer.

Treatment of soil washing wastewater via adsorption of lead and zinc using graphene oxide.

Abstract: In the present work, graphene oxide (GO) was synthesized via the modified Hummers method and utilized in treating real soil washing wastewater via adsorptive removal of lead (Pb) and zinc (Zn). Characterization analysis of GO was performed using X-ray diffraction, Brunauer-Emmett-Teller method, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and zeta potential analysis. The Van’t Hoff, Eyring, and Arrhenius equations were applied to determine the activation and thermodynamic parameters namely activation energy (Ea), standard Gibbs energy change (ΔG°), standard enthalpy change (ΔH°), standard entropy change (ΔS°), change in activation Gibbs energy (ΔG#), change in activation enthalpy (ΔH#), and change in activation entropy (ΔS#). Based on the high coefficient of determination values (0.8882 ≥ R2 ≥ 0.9094) and low values of SSE (0.0292 ≤ SSE ≤ 0.0511) and ARE (0.8014 ≤ ARE ≤ 0.8822), equilibrium data agreed well with the Freundlich isotherm. The maximum adsorption capacity for Pb(II) and Zn(II) was determined to be 11.57 and 4.65 mg/g, respectively. Kinetic studies revealed that pseudo-second-order equation fitted well with the experimental data, which indicates that chemisorption is the rate-determining step of the adsorption system. Results have shown the possibility of GO as a potential adsorbent material in the treatment of soil washing wastewater.