Oxygen stoichiometry,unit cell volume,and thermodynamic quantities of perovskite-type oxides

Perovskite-type oxides with A, A′=La, Ba, Sr; B, B′=Mn, Fe, Co were investigated by means of thermal analysis, solid electrolyte cells, and X-ray diffraction. Partial molar thermodynamic quantities are determined and their relations with O/M stoichiometry, unit cell volume, and phase stability were studied. The absolute values of partial molar enthalpies of perovskite-type oxides increase with increasing O/M stoichiometries and with decreasing unit cell volumes of the cubic perovskite-type structure, corresponding to higher chemical stabilities. The substitution of Ba for La, Ba for Sr, Co for Fe, and Fe for Mn lead to increase in unit cell volumes and decrease in absolute values of ΔH ⁰. The ΔH ⁰ values of the cobaltites/ferrites range from −33.5 kJ/mol for SrCo_0.8Fe_0.2O_3−x to −72.5 kJ/mol for La_0.2Sr_0.8Co_0.6Fe_0.4O_3−x, and of the manganates up to −132 kJ/mol for Ca_0.5Sr_0.5Mn_0.8Fe_0.2O_3−x .     

Accurate partition function for acetylene, 12C2H2, and related thermodynamical quantities

The internal partition function (Q(int)) of ethyne (acetylene), (12)C(2)H(2), is calculated by explicit summation of the contribution of all individual vibration-rotation energy levels up to 15,000 cm(-1). The corresponding energies are predicted from a global model and constants reproducing within 3σ all 18,415 published vibration-rotation lines in the literature involving vibrational states up to 8900 cm(-1), as produced by Amyay et al. [J. Mol. Spectrosc. 267, 80 (2011)]. Values of Q(int), with distinct calculations for para and ortho species are provided from 1 to 2000 K, in step of 1 K. The total internal partition function at 298.15 K is 104.224387(47) or 416.89755(19), with the nuclear degeneracy spin factors taken as 1/4:3/4 (astronomer convention) or 1:3 (atmospheric convention), respectively, for para:ortho species. The Helmholtz function, Gibbs enthalpy function, entropy, and specific heat at constant pressure are also calculated over the same temperature range. Accuracies as well as the missing contribution of the vinylidene isomer of acetylene in the calculations are discussed.     

Some thermodynamic quantities of n-alkanes as a function of chain length

Summary Results from high pressure dilatometry onn-alkanes and linear polyethylene and literature data yield a linear relation between specific volume, entropy and enthalpy of fusion, the reciprocal melting temperature and 1/n, wheren denotes the number of C-atoms per molecule. Extrapolating towards infiniten one always obtains polyethylene data.The differences in the properties ofn-alkanes and polyethylene can be ascribed to the influence of the chain ends. Assuming entropy and enthalpy contributions from these chain ends as made probable by a molecular model one can quantitatively explain then-dependence of the above mentioned quantities including their pressure dependence.With 10 figures and 2 tables     

Calculation of some thermodynamic properties of air plasmas: Internal partition functions,plasma composition,and thermodynamic functions

The thermodynamic properties of air plasmas are calculated in the framework of the C.L.T.E. hypothesis, for pressures varying from 1 to 200 atm, in a temperature range from 1000 to 30,000 K. In these calculations, the neutral mon--, di-, and triatomic species, as well as their positive and negative ions, are taken into account. From the internal partition function values, the plasma compositions and the thermodynamic functions (specific enthalpy, Gibbs and Helmholtz free energies and entropy) are calculated.     

Generalization of ionic partition diagrams to lipophilic compounds and to biphasic systems with variable phase volume ratios.

The ionic partition diagram methodology has been generalized to address both hydrophilic and lipophilic compounds and to consider biphasic systems with variable phase volume ratios. With this generalized approach electrochemical measurements of ion transfer potentials afford the determination of the standard partition coefficients of all forms of ionizable molecules, including the neutral form, as well as the evaluation of the dissociation constant of monoprotic substances. An interesting consequence of this approach is the definition of an extraction pK(a,ext) which is the apparent pK(a) of neutral acids and bases when dissolved in the organic phase.     

Experimental and thermodynamic study of solubility,partition and solvation of climbazole

Journal of Thermal Analysis and Calorimetry - The equilibrium solubility of climbazole (CLZ), an antifungal drug, was determined in buffers (pH 2.0; 7.4), hexane and 1-octanol within the...     

Cut-off criteria of electronic partition functions: effects on spectroscopic quantities

The influence of the cut-off criteria of electronic partition functions (Q_e) on absolute intensity of a spectral line and of the continuum in a     

Converged vibrational energy levels and quantum mechanical vibrational partition function of ethane

The vibrational partition function of ethane is calculated in the temperature range of 200-600 K using well-converged energy levels that were calculated by vibrational configuration interaction, and the results are compared to the harmonic oscillator partition function. This provides the first test of the harmonic oscillator approximation for a molecule with more than five atoms. The absolute free energies computed by the harmonic oscillator approximation are in error by 0.59-0.62 kcal/mol over the 200-600 K temperature range.     

Free volume quantities and viscoelasticity of polymer glasses

We have investigated, in terms of the Cohen-Turnbull theory, a relationship for polycarbonate (PC) glasses between average stress relaxation times, <to, and average free volume sizes, 〈v_f〉, obtained from positron annihilation lifetime spectroscopy. This examination suggests that the minimum free volume required for stress relaxation, v*, decreases with decreasing temperature and that, near the glass transition temperature, only a subset of extremely large free volume elements contributes to the stress relaxation of PC glasses. This suggestion is consistent with the idea that near the glass transition temperature, the viscoelastic response is dominated by large-scale, main-chain motion, whereas at lower temperature it is controlled by local motion. Moreover, comparison with the v* value estimated from gas diffusivity through various PC species at room temperature shows that the required free volume size for stress relaxation in the glass transition region is much larger than that for gas diffusion. Previously we showed that the Doolittle equation fails to correlate viscoelastic relaxation times of polymer glasses with changing temperature; determining the free volume fraction, h, from theoretical analysis of volume recovery data and theory, the Doolittle equation is shown to be valid in PC above 135°C (T_g - 14°C) irrespective of temperature and physical aging times. This result supports the idea suggested in the previous article that, as glassy polymers approach the transition region, viscoelastic properties increasingly tend to be controlled by free volume. © 1996 John Wiley & Sons, Inc.     

Organization of measurable thermodynamic quantities and their relevance to analytical chemistry

Summary A short discussion is given of the fundamentals of thermodynamics and of how the large number of measurable thermodynamic quantities can be organized in a clear and self-consistent way. The suggested Thermodynamic Family Tree also undelines the recent introduction of third order derivatives of Gibbs free energy as measurable properties with a sufficient accuracy. Those state functions are so new that they dont have a name nor a symbol yet! Finally some thoughts are given of how one should relate the thermodynamics to a recent discussion of H. Malissa [3] concerning the philosophy of analytical chemistry.

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Organisation meßbarer thermodynamischer Größen und ihre Bedeutung für die Analytische Chemie

Zusammenfassung Die Grundprinzipien der Thermodynamik werden kurz diskutiert und es wird gezeigt, wie die große Zahl meßbarer thermodynamischer Größen in ein klares und folgerichtiges System gebracht werden kann. Der vorgeschlagene thermodynamische Stammbaum zeigt die kürzlich eingeführten dritten Ableitungen der freien Gibbs-Energie als meßbare Eigenschaften mit befriedigender Genauigkeit. Diese Zustandsfunktionen sind so neu, daß sie noch keinen Namen und kein Symbol haben. Abschließend wird ausgeführt, wie die Thermodynamik zu einer kürzlichen Diskussion von Malissa über die Philosophie der analytischen Chemie in Beziehung gebracht werden kann.

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This paper was suggested by Professor Malissa of the Technische Hochschule Wien and should be considered a complement or extension to his important contribution to the discussion on the state and future of Analytical Chemistry (published in Fresenius Z. Anal Chem 305:97 (1981)     

S-Shaped composition dependence of excess thermodynamic quantities for cyclohexane mixtures with globular alkanes

Expansion coefficients , isothermal compressibilities, thermal pressure coefficients and heat capacities have been measured at 25°C for the cyclohexane+trans-decalin system. An S-shaped composition dependence, positivelnegative for highllow cyclohexane compositions is found for C _p ^E dV ^E /dT and the thermal expansion contribution to C _p ^E namely VT. The thermal motion contribution to C _p ^E , namely C _v is close to zero. The positive excursion of these mixing quantities at high cyclohexane content is anomalous. Correspondingly, the mixing quantity-VT deviates strongly in this region from the predicted equality with H ^E . The literature and this work show that all these excess quantities behave similarly for cyclohexane mixed with cyclooctane, methylcyclohexane and some highly branched alkanes. The unusual composition dependence of the thermodynamic quantities is consistent with order occurring when any large alkane molecule of globular shape is added to cyclohexane. This is speculatively associated with an interference by the globular alkane with the relatively free rotation of cyclohexane molecules.     

Emulsion polymerization: Determination of the average number of free radicals per particle by use of the number average volume of the particles

For emulsion polymerization in the zero order region (Interval II) a relation between the average number of free radicals per particle, n?(t), and the particle number average volume of a particle, v?_n(t), is derived as dv?_n(t)/dt = Kn?(t), where K is volume growth rate of a particle containing one free radical and is constant. This relation is also extended to copolymerization systems with an appropriate modification of the definition of K. By use of the data of particle size distribution (PSD), n? can be calculated without knowing the total number of particles. In conjunction with this relation, the recently developed light-scattering technique for measuring the PSD in addition to the conventional transmission electron microscope technique can provide a quick route for determination of n?. Styrene and methyl methacrylate emulsion homopolymerizations are taken as calculation examples.     

Freely jointed chain with variable segment number and length

The configurational properties of a molecular chain are investigated. The chain consists of rigid rod segments, which are consecutively correlated. This correlation is described by a two-state model. In the first state, neighboring segments are freely hinged togethers whereas in the second state they are parallel. The partition function and the force-extension relation are calculated. They show significant differences as compared to the usual results for a freely jointed chain. Thus the experimentally observed force-extension relation of polymeric networks buil up of such chains might be affected.     

硝基甲苯异构体的液晶溶液热力学性质的色谱法研究

本文用气液色谱方法研究了o-, m-, p-硝基甲苯三种异构体在双(对己氧基苯甲酸)对苯二酚酯(PBH~xB)和双(对庚氧基苯甲酸)对苯二酚酯(PBH~pB)两种向列液晶固定液中无限稀薄条件下的活度系数, 进而求得了超额焓, 超额自由能和超额熵, 同时得到溶解焓和溶解熵, 并对结果进行了分析和讨论。     

Oxidative thermal degradation of LDPE and the determination of some thermodynamic quantities

The pyrolysis of polyolefin wastes is one of the possible ways to obtain chemical feedstocks. In this work, the thermal degradation of low density polyethylene, (LDPE), which is a major product within plastics, was investigated in a semi-batch reactor system. First-order rate kinetics approach was chosen and reaction rate coefficients, k, and some thermodynamic quantities determined such as activation energy, reaction enthalpy, free activation enthalpy, and entropy of degradation of LDPE for different air flow rates. We found that the maximum value of some thermodynamic quantities, such as reaction rate coefficient is 0.0243 min⁻¹ at 600 mL min⁻¹ air flow rate and the free activation enthalpy (ΔG^≠) is 148.66 kJ mol⁻¹ at 450 mL min⁻¹ air flow rate and the reaction enthalpy (ΔH^≠) is 57.65 J mol⁻¹ at 623 K temperature conditions. Moreover, we found that the oxidative degradation of LDPE is not spontaneous and has lower energy necessary (for degradation) than non-oxidative degradation processes.     

A principle to correlate extreme values of excess thermodynamic functions with partial molar quantities

Excess thermodynamic properties are widely used quantitatively for fluids. It was found that at constant temperature and pressure a molar excess quantity of a mutually miscible binary mixture at the extreme points equals the excess partial molar quantities of the two components, i.e.F ^E ₁=F ^E ₂=F ^E _m, forming a triple cross point. The relationship is hold for properties such as enthalpy, entropy, Gibbs free energy, and volume, and is applicable for excess functions with multi extreme points. Solutions at extreme points can be referred to as special mixtures. Particularly for a special mixture of Gibbs free energy, activity coefficients of the two components are identical.     

Diffusion and partition coefficients of small organic solvents in molten miscible polymer blends: Correlations with thermodynamic interactions

The transport properties of small organic molecules in molten poly(vinyl chloride) (PVC)/atactic poly(methyl methacrylate) (PMMA) blends and their homopolymers were studied with inverse gas chromatography. The elution profiles resulting from various organic solvents and different experimental conditions were used for measuring diffusion and partition coefficients. With the van Deemter equation and retention volumes at infinite dilution, diffusion coefficients of 10^?7 to 10^?8 cm²/s and partition coefficients of 10–50 were calculated. The dependence of the diffusion and partition coefficients on experimental variables such as the blend concentration, temperature, and solute nature was examined. The presence of PMMA in PVC blends affected the sorption behavior of the PVC matrix up to a certain concentration. Beyond that, it was hard to derive any composition–diffusivity dependence. On the contrary, the diffusion and partition coefficients were greatly influenced by changes in the temperature and by the nature of the solute. For those solutes (e.g., chlorinated hydrocarbons) showing stronger interactions with polymer blends (higher negative values for the Flory–Huggins interaction parameter χ₁₍₂₃₎), higher diffusion and partition coefficients were obtained. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 267–279, 2004     

Ionization constants and thermodynamic quantities of 2-mercaptocarboxylic acids in aqueous solution

The carboxylic acid ionization constants of mercaptoacetic acid (MAA), 2-mercaptopropionic acid (2-MPA), 2-mercaptoisobutyric acid (2-MIBA) and 2-mercaptosuccinic acid (2-MSA) have been measured in perchlorate media at an ionic strength of 1.0M and over the temperature range 273–309°K. Appropriate thermodynamic quantities have been derived. The variation in the temperature T at which the constants exhibit a maximum has been interpreted in terms of the effect of hydrophobic substituents on the extent of solvation of the participating species.     

Reassessment of the binary, ternary, and quaternary interactions in mixed electrolytes from thermodynamic quantities: The systems with uncommon ions containing hydrophobic character

Accurate estimates of the binary, ternary, and quaternary interactions in aqueous ionic mixtures with uncommon ions with hydrophobic character are presented. For this purpose, the values of the excess Gibbs free energy of mixing, Delta m G(E), obtained from our earlier isopiestic osmotic coefficients (Kumar, A. J. Phys. Chem. B2003, 107, 2808) for the mixtures of NaCl with four guanidinium (Gn+) salts-CH3COOGn, GnNO3, GnClO4, and Gn2SO4-are analyzed with the help of the method developed by Leifer and Wigent. The methodology of Leifer and Wigent is based on the equations of Scatchard-Rush-Johnson and Friedman's cluster integral expansion theory. The Scatchard-Rush-Johnson theory explicitly considers the quaternary and higher-order ionic interactions in the mixtures as compared to the specific ion interaction theory of Pitzer, which accounts for binary and ternary interactions only. The contributions due to binary, ternary, and quaternary interaction terms to total Delta m G(E) are estimated and discussed critically. Also, the interaction between the same two cations, for example, Gn+ - Gn+, is estimated and found significant, which otherwise cannot be obtained by the use of Pitzer's theory. The information obtained from the analysis of Delta(m)G(E) is also supported by the newly measured excess volumes of mixing, Delta m V(E), at 298.15 K. The individual contributions of the binary, ternary, and quaternary interaction terms to total Delta m V(E) are described. The binary, ternary, and quaternary interaction terms for both Delta m G(E) and Delta m V(E) are analyzed in terms of Friedman's cluster integral expansion theory.