Showing papers on "Enthalpy published in 1975"
TL;DR: In this paper, the forbidden energy gap is used to obtain the standard Gibbs energy, enthalpy and entropy of formation of electrons and holes for each semiconductor up to the melting points.
Abstract: The forbidden energy gaps of Ge, Si, , and have been used to obtain the standard Gibbs energy, enthalpy and entropy of formation of electrons and holes for each semiconductor up to the melting points. The forbidden energy gap is the standard Gibbs energy of formation of electrons and holes and the enthalpy and entropy have been obtained from the energy gap as a function of temperature and familiar thermodynamic relationships. Energy gaps as a function of temperature, available in the literature, have been fit to the semiempirical equation of Varshni and used to extrapolate the energy gaps and thereby the three thermodynamic functions to the melting points. It is well known that the energy gaps, i.e., the Gibbs energies, decrease with increasing temperature but it is not well known that the enthalpy of formation increases with temperature and that it is proportional to the slope of the familiar logarithmic plot of the intrinsic carrier concentration over vs. . Examples of the utility of the enthalpy function are given. It is the entropy that leads to the decrease in energy gap with increasing temperature and its magnitude is large near the respective melting points (10–13 cals/deg, i.e.,) arising from the interactions of electrons and holes with the lattice. The intrinsic carrier concentrations were calculated from the forbidden energy gaps and the average effective masses which were estimated for the higher temperatures.
525 citations
TL;DR: The JANAF Thermochemical Tables cover the thermodynamic properties over a wide temperature range with single phase tables for the crystal, liquid, and ideal gas state as discussed by the authors. But the tables do not cover the properties of compounds.
Abstract: The thermodynamic tabulations previously published in NSRDS‐NBS‐37 and the 1974 supplement (J. Phys. Chem. Ref. Data 3, 311 [1974]) are extended by 158 new and revised tables. The JANAF Thermochemical Tables cover the thermodynamic properties over a wide temperature range with single phase tables for the crystal, liquid, and ideal gas state. The properties given are heat capacity, entropy, Gibbs energy function, enthalpy, enthalpy of formation, Gibbs energy of formation, and the logarithm of the equilibrium constant for formation of each compound from the elements in their standard reference states. Each tabulation lists all pertinent input data and contains a critical evaluation of the literature upon which these values are based. Literature references are given.
464 citations
TL;DR: In this paper, it is shown how differential scanning calorimetry (d.s.c.) data can be transformed to enthalpy curves which give Tg with an accuracy of ± 1K.
251 citations
TL;DR: In this paper, the vapour pressure of naphthalene over the temperature range 263 to 343 K was measured and correlated with data from the literature, and an equation was given from which recommended values were calculated for the vapor pressure of solid naphalene from 230 K to the triple point.
227 citations
TL;DR: Analysis of the variation of the apparent dimerization constant in the isodesmic mechanism sows that this self-association of calf brain tubulin is characterized by positive enthalpy, entropy, heat capacity, and molar volume changes, as well as the binding of one additional magnesium ion, which is probably not involved as a bridge between the protein molecules.
Abstract: The thermodynamic parameters of the magnesium ion induced self-association of calf brain tubulin in pH 7.0, 0.01 M phosphate buffer containing 10(-4) M GTP, were determined from sedimentation velocity experiments. This reaction proceeds by an isodesmic mechanism terminated by the highly favored formation of a closed ring shaped polymer of degree of association 26 +/- 4. Analysis of the variation of the apparent dimerization constant in the isodesmic mechanism s,ows that this self-association is characterized by positive enthalpy, entropy, heat capacity, and molar volume changes, as well as the binding of one additional magnesium ion, which is probably not involved as a bridge between the protein molecules. The addition of the last monomeric subunit has a free energy which is about three times that of dimer formation. Under the conditions of these experiments, tubulin binds 48 +/- 5 magnesium ions with a free energy of --2.8 kcal/mol.
117 citations
TL;DR: The effects of various ions and 2H2O on the thermal properties of phosphatidylcholine dispersions were studied using differential scanning calorimetry and the change in the surface potential of monolayers with temperature.
110 citations
TL;DR: In this paper, the molar excess enthalpy HE of (1 − x)H2O + xC2H5OH has been measured at 298.15, 323, 331, 343.15 and 363.15 K. The results are compared with available data from the literature and interpreted qualitatively by consideration of the molecular interactions in solution.
103 citations
01 Feb 1975
TL;DR: In this article, a discussion whether or not the contribution of water must be introduced into a thermodynamic equation of micellization was made on the basis of a phase separation model.
Abstract: A discussion whether or not the contribution of water must be introduced into a thermodynamic equation of micellization was made on the basis of a phase separation model. As a result, an enthalpy change on micelle formation at very low CMC can be fairly approximated by the conventional expression, ΔHm = − nRT2(∂ ln CMC/∂T)p. The contributions of hydrophilic and hydrophobic groups to the enthalpy change were investigated for the case of four kinds of sodium alkyl sulfates with different chain lengths from C8 to C14 over the temperature range from 10 to 55°C. It was found that the hydrophilic part has a major contribution at lower temperatures but at higher temperatures it gives a minor contribution, and that the hydrophilic part of ΔHm is always positive having a minimum around 40°C, while the hydrophobic part is always negative and decreases monotonically with temperature. Furthermore, the water around the hydrophilic head group was found to have a great effect on the CMC; when a parameter due to the water is selected properly, the degree of dissociation of micelle and other electrochemical properties at the micellar surface can be calculated to be the reasonable values.
92 citations
TL;DR: In this paper, a new equation of state applicable to lower reduced temperatures than the BWR equation of Starling and Han (BWRS equation) is proposed, adding four coefficients to their equation of eleven coefficients.
Abstract: A new equation of state applicable to lower reduced temperatures than the BWR equation of Starling and Han (BWRS equation) is proposed, adding four coefficients to their equation of eleven coefficients. Thermodynamic properties predicted by the two equations, such as density, enthalpy, isobaric heat capacity, f ngacity coefficient, vapor pressure, and vapor-liquid equilibrium, are compared to test the validity of the new equation of state. The ranges in which thermodynamic properties can be predicted, within about 10 % error, are extended down to 0.35 or below at reduced temperatures with the new equation. The limit for the prediction of saturated fugacity and vapor pressure for a pure substance, for instance, can be lowered from 0.47 with the BWRS equation to 0.32 with the new equation of state.
83 citations
81 citations
TL;DR: The small magnitude of the observed enthalpy change is in accord with the view that no large conformational change takes place in the deoxyhemoglobin S molecule upon gelation.
TL;DR: In this paper, the activation enthalpy for crystallization was observed to be (95 ± 5) kcal/mol, in good agreement with the activation entropy for viscous flow as determined previously by Chen.
Abstract: The crystallization kinetics of a Pd 0.775 Cu 0.06 Si 0.165 metallic glass have been determined by calorimetry over the temperature interval 665–680 K. We observe a change in the time dependence from t 4 at 665 K to t 3 at 680 K. In this temperature interval the activation enthalpy for crystallization was observed to be (95 ± 5) kcal/mol, in good agreement with the activation enthalpy for viscous flow as determined previously by Chen.
TL;DR: In this article, the forbidden energy gap is used to obtain the standard Gibbs energy, enthalpy and entropy of formation of electrons and holes for each semiconductor up to the melting points.
Abstract: The forbidden energy gaps of Ge, Si, , and have been used to obtain the standard Gibbs energy, enthalpy and entropy of formation of electrons and holes for each semiconductor up to the melting points. The forbidden energy gap is the standard Gibbs energy of formation of electrons and holes and the enthalpy and entropy have been obtained from the energy gap as a function of temperature and familiar thermodynamic relationships. Energy gaps as a function of temperature, available in the literature, have been fit to the semiempirical equation of Varshni and used to extrapolate the energy gaps and thereby the three thermodynamic functions to the melting points. It is well known that the energy gaps, i.e., the Gibbs energies, decrease with increasing temperature but it is not well known that the enthalpy of formation increases with temperature and that it is proportional to the slope of the familiar logarithmic plot of the intrinsic carrier concentration over vs. . Examples of the utility of the enthalpy function are given. It is the entropy that leads to the decrease in energy gap with increasing temperature and its magnitude is large near the respective melting points (10–13 cals/deg, i.e.,) arising from the interactions of electrons and holes with the lattice. The intrinsic carrier concentrations were calculated from the forbidden energy gaps and the average effective masses which were estimated for the higher temperatures.
01 Feb 1975
TL;DR: A FORTRAN IV subprogram called GASP as discussed by the authors calculates the thermodynamic and transport properties for 10 pure fluids: parahydrogen, helium, neon, methane, nitrogen, carbon monoxide, oxygen, fluorine, argon, and carbon dioxide.
Abstract: A FORTRAN IV subprogram called GASP is discussed which calculates the thermodynamic and transport properties for 10 pure fluids: parahydrogen, helium, neon, methane, nitrogen, carbon monoxide, oxygen, fluorine, argon, and carbon dioxide. The pressure range is generally from 0.1 to 400 atmospheres (to 100 atm for helium and to 1000 atm for hydrogen). The temperature ranges are from the triple point to 300 K for neon; to 500 K for carbon monoxide, oxygen, and fluorine; to 600 K for methane and nitrogen; to 1000 K for argon and carbon dioxide; to 2000 K for hydrogen; and from 6 to 500 K for helium. GASP accepts any two of pressure, temperature and density as input conditions along with pressure, and either entropy or enthalpy. The properties available in any combination as output include temperature, density, pressure, entropy, enthalpy, specific heats, sonic velocity, viscosity, thermal conductivity, and surface tension. The subprogram design is modular so that the user can choose only those subroutines necessary to the calculations.
TL;DR: In this article, structural parameters, vibrational fundamentals, and potential energy functions for internal rotation of n-butane and isobutane were evaluated by the direct sum of terms containing energy levels which were calculated with a one-dimensional potential model.
Abstract: Reported Values of Structural parameters, vibrational fundamentals, and potential energy functions for internal rotation of n‐butane and isobutane are reviewed. The selected values were used to calculate the thermodynamic properties (C°p, S°, (H°‐H°0)/T) in the temperature range of O to model. Contributions of internal rotation were evaluated by the direct sum of terms containing energy levels which were calculated with a one‐dimensional potential model. For internal rotation about the central C‐C bond in n‐butane, energy levels were approximated by two procedures. A inique potential function was assumed for each methyl rotor of n‐butane or of isobutane. Top‐top interactions in isobutane were approximated by the potential parameter V‐d6 which was determined empirically by comparison with thermodynamic data. The calculated and observed values of heat capacities and entropies agree well within experimental uncertainties. Standard enthalpies of formation of 298.15 K for the ideal gaseous state were selected from measured values of heats of combustion and third‐law enthalpies for isomerization. Corresponding values of ΔHf°, and log Kf are tabulated over the same temperature range.
TL;DR: In this article, a spectroscopic and thermodynamic study of aqueous dimethyl sulphoxide (DMSO) suggests that the properties of the system are dominated by direct component interaction.
Abstract: This spectroscopic and thermodynamic study of aqueous dimethyl sulphoxide (DMSO) suggests that the properties of the system are dominated by direct component interaction. Maximum inter-action occurs in the region of 0.35 mole fraction (DMSO) and “enhancement of water structure” by added solute is absent, except perhaps at very low concentration, < 0.01 mole fraction. The excess enthalpy HE, is compared with literature values.
TL;DR: In this article, the activation energy for the forward reaction step I (Ps + M (II) reversible PsM (I)) is generally very small; E/sub A/ approximately 1 kcal/mol.
Abstract: Evidence is presented which supports the reversible formation of molecular complexes between Ps atoms and a series of nitrobenzene derivatives and p-benzoquinone in solution. The activation energy for the forward reaction step I (Ps + M (II) reversible PsM (I)) is generally very small; E/sub A/ approximately 1 kcal/mol. $delta$H/sub EQ/, the enthalpy of the overall process, ranges from almost zero, in the case of very unreactive substrates, such as toluene or heptane, to -8 kcal/mol for dinitrobenzene or p-benzoquinone. The reactivities of the various substrate molecules toward Ps follow trends as observed in conventional molecular complex formation. Furthermore an attempt was made to assess the role of the solvent upon the stability of the molecular complexes. (auth)
PARC1
TL;DR: In this paper, the authors used differential scanning calorimetry to study the heat capacity and crystallization parameters of amorphous As 2 Se 3 and found that the capacity above the glass transition temperature exceeds, by a factor of 1.6, the Dulong-Petit limiting value found below T g.
Abstract: Through the use of differential scanning calorimetry, the heat capacity and crystallization parameters of amorphous As 2 Se 3 have been studied. It is found that the heat capacity above the glass transition temperature ( T g ) exceeds, by a factor of 1.6, the Dulong-Petit limiting value found below T g . The crystallization process is found to obey first-order kinetics with an activation enthalpy of 1.24 eV and an enthalpy of crystallization of 0.36 eV · molecule −1 . The effect of sample age on the rate constant is also reported.
TL;DR: In this paper, the heat capacities per unit volume of aqueous solutions of NaCl were measured with a flow microcalorimeter and the molality and temperature range covered were 0.01 to 3 mol kg −1 and 274.65 to 318.15 K. The calculated values of ΔH 2, φ agree within experimental uncertainty with the integral enthalpies of dilution of Ensor and Anderson and of Messikomer and Wood up to 323.15 k
TL;DR: In this paper, the available molecular parameters, fundamental frequencies, and enthalpy of formation for eight bromo-and indomethanes have been critically evaluated and recommended values selected.
Abstract: The available molecular parameters, fundamental frequencies, and enthalpy of formation for eight bromo‐ and indomethanes have been critically evaluated and recommended values selected. This information has been utilized to calculate the ideal gas thermodynamic properties. C°p, S°, H°−H°0, (G°−H°0)/T, ΔHF°, ΔGF°, and log KF from 0 to 1500 K using the rigid rotor‐harmonic oscillator approximation.
TL;DR: The foregoing results indicate that Glu-35 and Trp-62 are part of the contact, that perturbation oftrp-108 does not make a principle contribution to the concentration difference spectrum, and that no acid group other than Glu -35 is perturbed by self-association.
TL;DR: In this article, a simple formula is proposed to describe the pressure dependence of the variable Φ in El'yanov and Gonikberg's linear free energy relationship for ionization reactions in solution at high pressure.
Abstract: A simple formula is proposed to describe the pressure dependence of the variable Φ in El?yanov and Gonikberg's linear free energy relationship for ionization reactions in solution at high pressure. The expression, given in equations (10) and (12), provides a good description of the influence of pressure on ionization equilibria in aqueous solutions. It permits El'yanov's general linear relationships between Φ and ionization free energies, enthalpies and entropies, pH and Hammett's p parameter, to be expressed in terms of the pressure in convenient analytical forms. The formula is shown to be consistent with the simple electrostatic theory of ion hydration, allowing for the effect of pressure on the dielectric constant of water. Combined with the theory, it provides a general means of predicting ionization constants over a wide range of pressures and temperatures simply from knowledge of the changes in molar volume, enthalpy and entropy which accompany the reactions at atmospheric pressure.
TL;DR: It is concluded that the primary thermodynamic driving forces for the reaction are van der Waals interactions between the riboside moiety and the protein fabric and electrostatic interaction between the negatively charged phosphate group of the inhibitor and the positively charged histidine residues at the binding locus.
Abstract: The apparent free energy (deltaGapp) and enthalpy changes (deltaHB) associated with the interaction of 3'-cytosine monophosphate (3'-CMP) and ribonuclease A (RNase) are reported for the pH range 4--9, T = 25 degrees, mu = 0.05. The pH dependence of deltaGapp and deltaHB has been interpreted in terms of coupled ionization of histidine residues 12, 48, and 119, assuming that only the dianionic form of the inhibitor is bound. The results of this analysis are consistent with the calorimetric and potentiometric titration results for the free enzyme and its 3'-CMP complex reported in the previous paper (M. Flogel and R. L. Biltonen ((1975), Biochemistry, preceding paper in this issue). This analysis allows the calculation of the thermodynamic quantities associated with hypothetical but clearly defined reactions (e.g., the reaction of the dianionic inhibitor with the completely protonated enzyme). It is concluded that the primary thermodynamic driving forces for the reaction are van der Waals interactions between the riboside moiety and the protein fabric and electrostatic interaction between the negatively charged phosphate group of the inhibitor and the positively charged histidine residues at the binding locus. It is also suggested that the binding reaction is weakly coupled (approximately to 0.5 kcal/mol) with a conformational change of the protein associated with protonation of residue 48. These results are consistent with the model originally proposed by G. G. Hammes ((1968), Adv. Protein Chem. 23, 1) and lend additional quantitative detail to the nature of the reaction.
TL;DR: The ideal gas thermodynamic properties for ethylene and propylene in the temperature range 0 to 1500 K and at 1 atm have been calculated by the statistical thermodynamic method employing the most recent fundamental and molecular spectroscopic constants.
Abstract: The ideal gas thermodynamic properties [H °−H °0, (G°−H °0)/T, (H °−H °0)/T, S °, C °p, ΔHf °, ΔGf °, and log Kf] for ethylene and propylene in the temperature range 0 to 1500 K and at 1 atm have been calculated by the statistical thermodynamic method employing the most recent fundamental and molecular spectroscopic constants. The internal rational contributions to thermodynamic properties for propylene were generated based on an internal rotation partition function formed by summation of internal rotation energy levels. The energy levels were derived from the potential function V (cm−1) =349.2(1−cos 3ϑ)−6.5(1−cos 6ϑ). The calculated heat capacities and entropies were compared with the available experimental values.
01 Sep 1975-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, the rate of copper II extraction from acid nitrate solutions with LIX 64N was studied in a single drop reaction cell in which experimental conditions were conrrolled so that the back reaction kinetics were unimportant.
Abstract: The rate of extraction of copper (II) from acid nitrate solutions with LIX 64N was studied in a single drop reaction cell in which experimental conditions were conrrolled so that the back reaction kinetics were unimportant. Under these conditions the extraction reaction was found to be first order with respect to the cupric ion concentration, half order with respect to the concentration of the α-hydroxy oxime component of LIX 64N, and half order with respect to the concentration of the hydroxy-benzophenone oxime component of LIX 64N. Detailed consideration of the experimental results and the hydrodynamics of a falling drop system suggests that a surface reaction mechanism is rate controlling and that the reaction rate is not limited by mass transfer. The apparent activation enthalpy of approximately 6.5 kcal/mole (27.2 kJ/mole) was found to be essentially independent of the variables considered.
TL;DR: In this paper, the total pressure for the system of isopropanol and water was measured in a temperature range from 35 to 75°C by using a modified Othmer recirculation still.
Abstract: Total pressure for the system of isopropanol and water was measured in a temperature range from 35 to 75°C by using a modified Othmer recirculation still. The vapor-liquid equilibrium was calculated from the total pressure-composition data by using the numerical method of Barker. Simultaneous fitting of the excess Gibbs energy and the excess enthalpy data was successfully done by using the Wilson equation.
TL;DR: In this paper, the effects of complex formation between propionic acid and aniline in the following molar relation: 2CH3CH2COOH·C6H5NH2.
Abstract: Viscosities, densities, refractive indices, and enthalpies at 25 °C were determined for the systems: propionic acid + aniline (PA + A ), propionic acid + N,N-dimethylaniline (PA + DMA ), and propionic acid + pyridine (PA + P). From the experimental results the excess volume, excess viscosity, excess molar free energy of activation, and excess enthalpy were calculated. The deviations from ideality for the excess thermodynamic functions are more important for the systems PA + A and PA + P than for PA + DMA. There is evidence for complex formation between propionic acid and aniline in the following molar relation: 2CH3CH2COOH·C6H5NH2.
TL;DR: In this paper, the enthalpy of dissociation of aqueous ammonium ion, ΔHo(NH4+), can be represented in this temperature range by ΔH o (NH 4 + )/kJ mol −1 = 48.49 + 0.0114 T K.
TL;DR: In this paper, a flow calorimeter capable of measuring excess enthalpies of liquids at temperatures and pressures up to 473 K and 1.6 MPa is described.