Showing papers on "Enthalpy published in 1980"
01 Oct 1980
TL;DR: In this paper, a linear relationship between the standard free energy, the enthalpy and the entropy of n-alkanes was found, and the number of carbon atoms was found.
Abstract: The Henry's law region of the adsorption isotherms for a series of n-alkanes on cotton cellulose and on wood fibers has been studied by gas chromatography. On wood fibers, the three thermodynamic functions at zero surface coverage were determined. A linear relationship between the standard free energy, the enthalpy and the entropy, and the number of carbon atoms was found. Attempts were made to estimate the London contribution to the surface free energy of cellulose and wood fibers from the results at infinite dilution. A method based on the increment per CH2 group in the free energy of desorption, normalized per unit area of a methylene group, is in reasonable agreement with other estimates.
550 citations
TL;DR: In this article, the authors used experimental methane-krypton and methane-argon hydrate data to generate chemical-potential, enthalpy, and heat-capacity functions for Structure I hydrates for temperatures between -190/sup 0/ and 80/Sup 0/F (150 and 300 K) using a modified statistical model where the gas-water interactions were calculated from the spherical core Kihara intermolecular pair potential function.
Abstract: Because hydrate formation in pipelines, processing operations, and reservoirs is generally undesirable, studies of gas-hydrate thermodynamics, particularly examinations of conditions where a second hydrate phase or a hydrocarbon-rich phase exists in addition to the water, hydrate, and gas phases, are important to the natural gas industry. In this study, analysts used experimental methane-krypton and methane-argon hydrate data to generate chemical-potential, enthalpy, and heat-capacity functions for Structure I hydrates for temperatures between -190/sup 0/ and 80/sup 0/F (150 and 300 K). These properties were based upon a modified statistical model where the gas-water interactions were calculated from the spherical-core Kihara intermolecular pair potential function. (The model does not use any adjustable parameters that depend upon the gas species present.) Estimates of the Kihara water-energy and water-distance parameters were -251.57/sup 0/F (115.46 K) and 375.06 pm, respectively. The mixing rules for the Kihara parameters are probably the weakest point of the model, but they are necessary to the corresponding-states approach for predicting the hydrate phase equilibrium. Although the model does not allow satisfactory predictions for larger or highly asymmetric hydrate-forming molecules (such as propane and isobutane), the results of this study can serve as a base for modificatins that account for bothmore » size and asymmetry.« less
351 citations
TL;DR: The vapor pressure of H2SO4 over 98.01 mass-% sulfuric acid solution has been determined experimentally over the temperature interval 338 to 445 K as mentioned in this paper, which is consistent with other estimates available in the literature.
Abstract: The vapor pressure of H2SO4 over 98.01 mass-% sulfuric acid solution has been determined experimentally over the temperature interval 338 to 445 K. Values of the enthalpy and entropy changes upon vaporization deduced from the data accord well with other estimates available in the literature. Extrapolation to 99.0 mass-% and 296.15 K allows us to confirm another recent vapor pressure determination, thereby supporting the conclusion that the vapor pressures most often used in nucleation calculations in the past are as much as an order of magnitude high.
224 citations
TL;DR: In this article, the enthalpic voltage, the higher heating value voltage, and the thermoneutral voltage were derived for the reversible potential, as functions of temperature between 25° and 250°C and of pressure between 1 and 100 atm.
Abstract: Precise definitions are given of three thermodynamic parameters which characterize the water‐electrolysis reaction: the enthalpic voltage, the higher‐heating‐value voltage, and the thermoneutral voltage. Expressions are derived for these parameters and for the reversible potential, as functions of temperature between 25° and 250°C, and of pressure between 1 and 100 atm. Heat losses due to radiation, convection, and conduction are also considered, and a thermal‐balance voltage is defined; representative values are calculated. Electrical‐energy efficiency is related to the characteristic parameters, and thermodynamic limitations on its value are discussed.
171 citations
TL;DR: In this paper, enthalpies of solution in 2PbO· B2O3 at 712°C have been measured for glasses in the systems albite anorthite diopside, NaAlO2-SiO2, Ca0.5AlO 2-Si O2 and albite-anorthite-quartz.
141 citations
TL;DR: In this article, the enthalpy of metal atoms on metallic substrates can be calculated by means of a semi-empirical model in which metal atoms are treated as if they were macroscopic pieces of metal.
126 citations
TL;DR: In this article, the specific heat, enthalpy, and entropy of coal, char, tar, and ash as a function of temperature and material composition are presented. But the standard entropy for coal is approximated by comparing the behavior of the standard entropies of a number of aliphatic and aromatic hydrocarbons.
110 citations
TL;DR: In this article, the first neutral for a series of negative ions was found to parallel the gas-phase basicity of those anions, and the order of the magnitude of the enthalpy changes on the association of the neutral was determined.
Abstract: Ion-molecules association reactions of the form A(-)(B)n-1 + B = A(-)(B)n were studied over a range of temperatures in the gas phase using high pressure mass spectrometry. Enthalpy and entropy changes were determined for the stepwise clustering reactions of (1) sulfur dioxide onto Cl(-), I(-), and NO2(-) with n ranging from one to three or four, and onto SO2(-) and SO3(-) with n equal to one; and (2) carbon dioxide onto Cl(-), I(-), NO2(-), CO3(-), and SO3(-) with n equal to one. From these data and earlier hydration results, the order of the magnitude of the enthalpy changes on the association of the first neutral for a series of negative ions was found to parallel the gas-phase basicity of those anions.
107 citations
01 Jan 1980
TL;DR: In this paper, a statistical method has been developed which tests for true compensation, which can be applied to problems in organic chemistry, protein-enzyme-water reactions, microbial death, and food deterioration.
Abstract: Chemical reactions occurring in foods obey the laws of thermodynamics. Temperature affects reaction rates according to enthalpy/entropy kinetics. Complex food systems can be made to fit mathematical equations for free energy changes. Three models for describing the relation of temperature to reaction rate include the Arrhenius, collision theory, and activated complex theory models. Some rate processes produce a straight line when enthalpy changes are plotted against entropy changes; the slope of this line is the isokinetic temperature and this relationship is defined as enthalpy/entropy compensation. Enthalpy/entropy compensation is a property of proteins in food reactions and may contribute to the stability of proteins. A statistical method has been developed which tests for true compensation. Enthalpy/entropy compensation analysis can be applied to problems in organic chemistry, protein-enzyme-water reactions, microbial death, and food deterioration
100 citations
01 Apr 1980
TL;DR: In this paper, a program subroutine FLUID calculates thermodynamic and transport properties of pure fluids in liquid, gas, or two-phase (liquid/gas) conditions.
Abstract: Computer program subroutine FLUID calculates thermodynamic and transport properties of pure fluids in liquid, gas, or two-phase (liquid/gas) conditions. Program determines thermodynamic state from assigned values for temperature and density, pressure and density, temperature and pressure, pressure and entropy, or pressure and enthalpy.
93 citations
TL;DR: The elementary transition state approach has been used to obtain a simple model theory for the Soret effect (thermal diffusion) and the Dufour effect, and the results conform to the Onsager reciprocal relationship.
Abstract: The elementary transition state approach has been used to obtain a simple model theory for the Soret effect (thermal diffusion) and the Dufour effect. The flow of heat in the Dufour effect is identified as the transport of the enthalpy change of activation as molecules diffuse. The theory as now formulated applies only to thermodynamically ideal mixtures of substances with molecules of nearly equal size. The results of the theory conform to the Onsager reciprocal relationship. When the results were fit to data on thermal diffusion for two liquid systems, a close fit was obtained and yielded reasonable values of between 2 and 3 kcal mol-1 for enthalpy changes of activation and differences between the entropy changes of activation for the two components of between 0 and 1 cal K-1 mol-1.
TL;DR: In this paper, the effect of a varying heating rate on the crystallization temperature was studied in amorphous Th-Fe alloys and it was shown that the proportionality between the crystallisation temperature and the hole formation enthalpy is quite generally valid.
TL;DR: In this article, the enthalpy changes on interaction of a series of sodium n-alkyl sulphates with lysozyme have been measured by microcalorimetry at 25°C in aqueous solution at pH 3.2 and 9.0.
Abstract: The enthalpy changes on interaction of a series of sodium n-alkyl sulphates with lysozyme have been measured by microcalorimetry at 25°C in aqueous solution at pH 3.2 and 9.0. The enthalpy of interaction increases with increase in alkyl chain length and decrease in pH. Sodium n-decyl and n-dodecyl sulphates initiate a conformation change in lysozyme which makes an endothermic contribution to the overall enthalpy of interaction at high binding levels. Measurements of the binding isotherms and enthalpies of interactions of sodium n-dodecyl sulphate with derivatives of lysozyme in which the cationic residues lysyl, arginyl and histidyl have been chemically modified lead to the view that ionic groups are largely responsible for the initial exothermic interaction of the surfactant with the protein.
TL;DR: In this paper, the UNIQUAC/UNIFAC models are modified by the introduction of a general temperature dependence of the coordination number, which leads to considerable improvements of the simultaneous correlation.
TL;DR: In this paper, the Gibbs free energies of formation for the aqueous species have been computed; these are presented with entropy and enthalpy values where available where available, and the selected thermodynamic values are tabulated.
TL;DR: In this paper, the gas-phase clustering equilibria of NO2 and NO3 were determined with high-pressure mass spectrometry, and a comparison of values of the free energy of hydration derived from the data shows good agreement with formerly reported values at 296 K.
Abstract: Thermodynamic quantities for the gas-phase clustering equilibria of NO2(-) and NO3(-) were determined with high-pressure mass spectrometry. A comparison of values of the free energy of hydration derived from the data shows good agreement with formerly reported values at 296 K. New data for larger NO2(-) and NO3(-) hydrates as well as NO2(-)(HNO2)n were obtained in this study. To aid in understanding the bonding and stability of the hydrates of nitrite and nitrate ions, CNDO/2 calculations were performed, and the results are discussed. A correlation between the aqueous-phase total hydration enthalpy of a single ion and its gas-phase hydration enthalpy was obtained. Atmospheric implications of the data are also briefly discussed.
TL;DR: In this article, two dominant selenium-related defects in silicon have been studied by transient capacitance and current techniques, and the authors obtained a temperature dependence of 3×10−15 cm2 at 100 K.
Abstract: Two dominant selenium‐related defects in silicon have been studied by transient capacitance and current techniques. For one of the centers, the A center, Arrhenius plots of thermal emission rates for electrons and holes (log et−1/T) give ’’thermal activation energies’’ of EC −ET =0.52 eV and ET −EV =0.62 eV, respectively. Although the electron‐capture cross section of the center is too large to be measured with our equipment, a conservative estimate gives a value larger than 10−14 cm2. The electron‐capture cross section σtnB of the other center, the B center, showed a T−3.2 temperature dependence and has a value of 3×10−15 cm2 at 100 K. From the measured data for σtnB and etnB a value of 0.30 eV for the Gibbs free energy of the B center is obtained. This energy value is constant and equal to the enthalpy in the temperature range investigated. Plotting log T2σtnB versus 1/T, an activation energy of 14 meV is obtained. This is interpreted as the energy separation between the lowest state accessible in a cas...
TL;DR: In this paper, high pressure CO2 sorption data in polycarbonate (PC) were reported as a function of temperature and thermal history, and the bulk physical structural changes produced by annealing at 125 and 135°C were monitored by density and thermal property changes.
Abstract: High pressure CO2 sorption data in polycarbonate (PC) are reported as a function of temperature and thermal history. The bulk physical structural changes produced by annealing at 125 and 135°C were monitored by density and thermal property changes. The sorption data are analyzed by the dual sorption model which assumes the sorption isotherm to consist of Henry's law and Langmuir sorption terms; The Langmuir capacity term C of PC can be grossly correlated with the reported volumetric parameters of the polymer. This excess volume interpretation of C has found support in the good correlation between C and the corresponding enthalpy relaxation from parallel Differential Thermal Analysis of the samples. Density measurements provide gross evidence of the free volume interpretation of C. The experimental uncertainties in the data compromise a more critical test of the relationship between C and the density of annealed samples.
TL;DR: In this paper, the authors developed a method that allowed the prediction of self-diffusion coefficients at any temperature and pressure from a single diffusion measurement and from the values of the expansivity and the isothermal bulk modulus.
Abstract: In a former paper [Phys. Rev. B 22, 3130 (1980)] the authors developed a method that allowed the prediction of self-diffusion coefficients at any temperature and pressure from a single diffusion measurement and from the values of the expansivity and the isothermal bulk modulus. In this paper the study is extended to heterodiffusion. Applications are presented for carbon diffusing in $\ensuremath{\alpha}$-iron, antimony diffusing in copper, and zirconium diffusing in niobium. Furthermore, from a single diffusion measurement the activation enthalpy for various temperatures can be succesfully calculated.
TL;DR: In this article, the conformational enthalpy differences and conformational entropy differences for methyl, ethyl, and isopropyl groups in alkylcyclohexanes were investigated at low temperatures of solutions in CFCl3-CDCl3.
Abstract: 13 C N.m.r. studies at low temperatures of solutions in CFCl3–CDCl3 of [Me-13C]methylcyclohexane, [α-13C]-isopropylcyclohexane, cis-1-ethyl-4-methylcyclohexane, cis-1-isopropyl-4-methylcyclohexane, and cis-1-ethyl-4-isopropylcyclohexane have yielded conformational enthalpy differences and conformational entropy differences for methyl, ethyl, and isopropyl groups in alkylcyclohexanes. For –ΔH°, the averaged values obtained, in kcal mol–1, were 1.75 (Me), 1.60 (Et), and 1.52 (Pri); for ΔS°, the averaged values, in cal mol–1 K–1, were –0.03 (Me), 0.64 (Et), and 2.31 (Pri). The determined values are in good agreement with those calculated by the Allinger group for the gas phase, using a method based on classical mechanics. As a result of the opposing trends for –ΔH° and ΔS° values, the sequence of –ΔG° values at 300 K, namely Pri > Et > Me, is reversed at temperatures below ca. 40 K.
TL;DR: In this paper, the effects of pressure, temperature, and some variations in impurity content on the growth rate u of quartz into fused silica were measured, and under all conditions u was interface controlled and increased exponentially with pressure with an activation volume averaging -21.2 cu cm/mole.
Abstract: The effects of pressure, temperature, and some variations in impurity content on the growth rate u of quartz into fused silica were measured. Under all conditions the growth rate was interface controlled and increased exponentially with pressure with an activation volume averaging -21.2 cu cm/mole. The activation enthalpy for all specimens is extrapolated to a zero pressure value of 64 kcal/mole, within the experimental uncertainty. At a given stoichiometry the effect of hydroxyl content on growth rate is described entirely by a linear term C(OH) in the prefactor of the equation for the growth rate. The effect of chlorine impurity can be described similarly. Also u is increased as the ideal stoichiometry is approached from the partially reduced state.
TL;DR: In this article, it was shown that the growth of quartz crystals into fused silica is effected by a mechanism involving the breaking of an Si-O bond and its association with an OH group, followed by cooperative motion of the nonbridging oxygen and the hydroxyl group which results in the crystallization of a row of several molecules along a crystalline-amorphous interfacial ledge.
Abstract: It is proposed that the growth of quartz crystals into fused silica is effected by a mechanism involving the breaking of an Si-O bond and its association with an OH group, followed by cooperative motion of the nonbridging oxygen and the hydroxyl group which results in the crystallization of a row of several molecules along a crystalline-amorphous interfacial ledge. This mechanism explains, at least qualitatively, all the results of the earlier experimental study of the dependence of quartz crystal growth upon applied pressure: large negative activation volume; single activation enthalpy below Si-O bond energy; growth velocity constant in time, proportional to the hydroxyl and chlorine content, decreasing with increasing degree of reduction, and enhanced by nonhydrostatic stresses; lower pre-exponential for the synthetic than for the natural silica.
TL;DR: In this paper, the apparent solubility product of calcite was measured by saturometry as a function of temperature and salinity, and an equation was fitted to the experimental data, resulting in pK′sp = 6.5795 − 3.3.
TL;DR: In this paper, an improved formulation for the orientation-dependence of multi-layer surface segregation is developed in terms of bond enthalpy and strain energy minimization, and the conditions for the existence of an extremum in the surface energy isotherm, originally derived by Defay et al. from a monolayer model, are re-examined on the basis of a multi layer model.
TL;DR: In this paper, the enthalpies of mixing of aqueous glycine and metal chloride solutions have been investigated at 298.15 K using a microcalorimetric method.
Abstract: The enthalpies of mixing of aqueous glycine and aqueous alkali metal chloride solutions have been investigated at 298.15 K using a microcalorimetric method. The salts investigated were LiCl, NaCl, KCl and CsCl. The experimental data have been used to determine pairwise enthalpy of interaction coefficients and from these and earlier corresponding free energy coefficients the entropy coefficients have been obtained. The results indicate that the lithium ion interacts with glycine in a markedly different way to the other cations, even though the free energy coefficients are quite similar.
TL;DR: In this article, the temperature dependency of the n -octanol water partition coefficient and the hydrophobic substituent constant, π, for a series of substituted phenols has been determined.
TL;DR: In this paper, the debye-Huckel limiting slopes for the osmotic coefficient, A, derived from literature measurements of the static dielectric constant and density of water, are properly represented as a function of temperature by a general thermodynamic equation, determined using the method of weighted least-squares.
Abstract: Debye–Huckel limiting slopes for the osmotic coefficient, A, derived from literature measurements of the static dielectric constant and density of water, are properly represented as a function of temperature by a general thermodynamic equation, determined using the method of weighted least-squares. From 0 to 150°C and between atmospheric and the water-saturation pressure, A is best represented by an equation equivalent to
A=–16.390 23 + 261.3371/T+ 3.368 9633 ln T–1.437 167(T/100)+ 0.111 995(T/100)2 where T/K = 273.15 +t/°C IPTS-68. Minimum variance, unbiased estimates of the values and their standard errors are tabulated for A and for the limiting slopes for the solute enthalpy, AL, and heat capacity, AJ.
TL;DR: In this article, a series of compounds of the general formula (n -C n H 2 n +1 NH 3 ) 2 MCl 4 (where M is a divalent metal atom and 8 ⩽ n⩽ 18) undergoing high enthalpy reversible solid-solid phase transitions is considered.
01 Jun 1980
TL;DR: In this article, isotherms of the surface excess amount and integral enthalpy of displacement of dilute solutions of the n -paraffins n -C 22 H 46, n -c 28 H 58, and n - c 32 H 66 and of 2,6,10,15,19,23-hexamethyltetracosane (squalane) from n-heptane onto graphitized carbon black have been measured at 298°K (298-318°K in some cases).
Abstract: Isotherms of the surface excess amount and of the integral enthalpy of displacement of dilute solutions of the n -paraffins n -C 22 H 46 , n -C 28 H 58 , and n -C 32 H 66 and of 2,6,10,15,19,23-hexamethyltetracosane (squalane) from n -heptane onto graphitized carbon black have been measured at 298°K (298–318°K in some cases). The molar enthalpies of displacement of the n -paraffins are high (−60 to −95 kJ mol −1 ) and contain a large contribution caused by lateral interactions of the long-chain solute molecules which are adsorbed side by side on the graphite basal plane. The isotherms of n -C 22 H 46 are Sshaped and can be accounted for by the parallel layer model , with a high value of the Flory—Huggins parameter for the adsorbed layer ( χ a ⋍ 2.2 ). The submonolayer region of the “high-affinity” isotherms of n -C 32 H 66 , which has been studied by an elution method, gives evidence of a cooperative adsorption mechanism in this system too. In contrast, squalane is not strongly adsorbed onto the graphite basal plane from n-heptane. The side groups of this molecule prevent a close packing of the chains on the surface; as a consequence, the contributions of solid-adsorbate interactions and of adsorbate—adsorbate interactions to the enthalpy of displacement are small for this system.