Enthalpy Of Formation ΔH Research Articles

First-Principles Calculations of Stable Geometric Configuration and Thermodynamic Parameters of Cadmium Sulfide Thin-Film Condensates

Thin-film CdS layers obtained by the open evaporation method in vacuum are considered and cluster models for calculation of crystal, band structure and thermodynamic parameters are proposed. The thermodynamic parameters of the formation energy ΔE, enthalpy of formation ΔH, Gibbs energy ΔG, entropy ΔS and specific heat capacities at constant pressure and volume for cubic and hexagonal crystallographic modifications are determined. The stable crystal structure for cadmium sulfide was determined from the analysis of Gibbs energy temperature dependences for the sphalerite and wurtzine phases.

Infrared studies of weak B…HCl (B = HCl, CO, Xe, N 2) complex formation in solid Kr solutions

IR spectra of small B…HCl (B = HCl, N 2, Xe, CO) complexes have been studied in solid phase at equilibrium conditions by using the technique of crystal growth from a liquid Kr solution. Triplet to doublet structure evolution of the ν(HCl) fundamental band has been revealed at liquid to crystal state transition of the noble (Xe, Kr) gas solutions. Residual rotational structure observed at wings of the ν(HCl) band and spectral moments analysis suggest that noncomplexed HCl molecules continue to rotate in solid solutions studied. Self-association of HCl molecules has been found in solid Kr, while this process was strongly suppressed in solid Xe. Spectral parameters of the ν c fundamental bands and enthalpy of formation ΔH were estimated for B…HCl complexes in solid Kr. Comparative analysis of the ν c (CO) and ν c (HCl) bands shows that the ν c (HCl) bands is perturbed due to intermolecular H-bonding and the OC…HCl complex does not rotate in solid Kr. Relative changes of the integral intensity A of the fundamental ν c (HCl) and ν c (CO) bands due complex formation have been derived from the temperature dependence of the A value.

The enthalpy of formation of trioxy radicals ROOO (R  H, CH 3, C 2H 5). An ab initio study

Enthalpies of formation of trioxy radicals, ROOO, with R  H, CH 3, and C 2H 5, are calculated, along with values for the corresponding species R, RO, RO 2, RO 2H, and RO 3H using the G2M(RCC) approach, a modified Gaussian-2 model extrapolating the RCCSD(T)/6-311 + G(3df,2p) level of theory. Where applicable, CBS-QCI/APNO calculations were performed. The enthalpy of formation ΔH f 0(298K) of cis-HOOO ( 2A″) was determined to be 6.1 kcal/mol using the CBS-QCI/APNO model. The HO-OO bond dissociation energy was calculated using the G2M(RCC) formalism to be +1.31 kcal/mol for 0K which is very close to the result of +1.15 kcal/mol using the CBS-QCI/APNO model. The CH 3O-OO and C 2H 5O-OO bond energies were calculated to be −0.87 (G2M(RCC)) and −0.5 kcal/mol (G2M(RCC,MP2)).

Dipole moments of exciplexes of heteroaromatic compounds with N, N-dimethylaniline

The influence of the polarity of a solvent on the position of the maximum of the fluorescence band of exciplexes of N, N-dimethylaniline (DMA) with exctied molecules of phenazine, acridine, and their benzo-, dibenzo- and tetrabenzo derivatives was studied. From the regularities found, the Μ2/γ3h values were evaluated, giving an estimate of the dipole moments of the exciplexes under consideration. An attempt was made to find a correlation between Μ2/ϱ3h values and the value of the enthalpy of formation δH of the corresponding excited complexes. It was concluded that for the first members of the azine series, the Μ2/ρ3h value does not reflect the degree of charge transfer in the exciplex, and cannot be correlated with AH. Explanations are presented which give as the main reason for this lack of correlation the possible conformational changes undergone by the excited molecules of azines during the formation of the exciplexes.

ChemInform Abstract: ENTHALPIES OF FORMATION OF NAPHTHALENE TCNQ, ANTHRACENE TCNQ, TMPD, AND TMPD TCNQ, AND EXPERIMENTAL CRYSTAL BINDING ENERGIES OF MIXED SIMPLE REGULAR LATTICES

The standard enthalpies of formation ΔH°f[naphthalene TCNQ(c), 298.15 K]=716.95±7.30 kJ/mol, ΔH°f[anthracene TCNQ(c), 298.15 K] =763.84±4.87 kJ/mol, and ΔH0f[TMPD(c), 298.15 K]=39.60±3.85 kJ/mol were measured by oxygen combustion calorimetry. Then, the states naphthalene TCNQ(c), anthracene TCNQ(c), and TMPD TCNQ(c) are more stable by 30.01±7.63, 30.31±5.26, and 82.08±4.34 kJ/mol than the states [naphthalene(c), TCNQ(c)], [anthracene(c), TCNQ(c)], and [TMPD(c), TCNQ(c)], respectively; they are more stable than the gaseous neutral ions by 203±12, 232±12, and 230±10 kJ/mol, respectively. Therefore, the choices of different lattices and ionicities are determined not by the thermochemical results given above, but by a subtle interplay between the cost of ionization ID–AA and the various charge‐dependent contributions to the theoretical cohesive energy.

Heat capacities and thermodynamic functions of LaNi 5, LaNi 5H 0.36 and LaNi 5H 6.39 from 5 to 300 K

The heat capacities of LaNi 5 and the hydrides α-LaNi 5H 0.36 and β-LaNi 5H 6.39 were measured using adiabatic calorimetry in the temperature range 5–300 K. The special techniques required to prepare the hydrides in small copper sample capsules for loading into the calorimeter are described. The calculations for the heat capacities include a correction for the change in the equilibrium hydrogen pressure in the gas space above the hydride samples when the samples were heated during the calorimetric measurements. The heat capacities of LaNi 5, α-LaNi 5H 0.36 and β-LaNi 5H 6.39 in the temperature range 5–300 K show no anomalous behavior except possibly for a slight enhancement of the heat capacity of β-LaNi 5H 6.39 between 120 and 160 K. The entropies of formation of α-LaNi 5H 0.36 and β-LaNi 5H 6.39 from hydrogen and LaNi 5 were found to be −107.2 ± 6 and −111.2 ± 0.5 J K −1 (mol H 2) −1 respectively at 298.15 K. The enthalpy of formation ΔH β of β-LaNi 5H 6.39 was calculated from our calorimetric results and from a hydrogen absorption isotherm and was found to vary with temperature; thus ΔH β = −29.20, −30.24 and −30.40 kJ (mol H 2) −1 at 195, 273.15 and 298.15 K respectively. The entropy and enthalpy results derived from this investigation are discussed and are compared with other results in the literature.

Enthalpy of formation and excess entropy for dilute copper-based alloys: Experimental and theoretical study

Enthalpy of formation ΔH and excess free enthalpy G E of the binary dilute solutions Cu-M, where M goes from Ti to Ge in the periodic table, have been measured by liquid tin calorimetry ( ΔH) and solid galvanic cell experiments ( G E ). In the case of transition impurities in copper a simple one-electron theory provides the general features for the initial slope of the energy ΔE (or enthalpy ΔH) of formation. However for Fe, Mn, and Cr impurities experimental results confirm that it is necessary to take into account the magnetic decoupling of the impurity states. The double origin of the excess entropy ΔS E , i.e. vibrational and magnetic, is calculated. The comparison with the experimental results showed that for Ni, Fe and Co the spin fluctuations represent a very important part of ΔS E .

Calorimetric investigation of the liquid alloys of Ag + Te and of the Ag 2Te solid compound at high temperature

The enthalpies of formation ΔH f of Ag+Te alloys have been measured in the temperature range 728 < T K < 1378 , by direct reaction calorimetry. At 1210 K, the highest temperature investigated, the enthalpy of formation of Ag 2Te solid compound is −15.90 kJ mol −1 with reference to solid Ag and liquid Te. The study of its variation with temperature yields a negative excess heat capacity, C p E = −3.8 J K −1 mol −1, in the same reference state. In the liquid state, the integral enthalpy of formation shows a sharp minimum at x Te = 0.333, corresponding to the formation of Ag 2Te-type associates and the partial molar enthalpy of tellurium undergoes a jump at this mole fraction as predicted by C. Wagner many years ago. The fact that in the liquid state, ΔH f is temperature independent up to 1378 K, indicates a high stability of these associates.

Hydrides of LaNi and CeNi intermetallic compounds

The hydriding characteristics of La 7Ni 3, LaNi and Ce 7Ni 3 have been investigated. These compounds form the stable hydrides La 7Ni 3H 19.3, LaNiH 3.85 and Ce 7Ni 3H 19.2. In structural and magnetic investigations La 7Ni 3is found to decompose into LaH 3 and LaNi 5 on rapid hydrogenation. On desorption at elevated temperatures the original La 7Ni 3 structure is reformed. An analogous decomposition is found in Ce 7Ni 3. The enthalpies of formation ΔH have been measured calorimetrically for the hydrides of LaNi compounds. ΔH varies linearly with the LaNi composition, independently of the various compound structures and of structural transformations on hydrogenation. The experimental values of ΔH are described by a phenomenological model. Despite their high hydrogen content, these hydrides are not suitable for use as hydrogen storage materials because of their high stability.

Heat of formation of bis(η-cyclopentadienyl)dimethyltungsten and bis(η-cyclopentadienyl)dimethylmolybdenum

Bond-enthalpy contribution values D(Mo–Me)= 149·5 kJ mol–1 and D(W–Me)= 197·8 kJ mol–1 have been derived from the standard enthalpies of formation ΔH°f[Mo(η-C5H5)2Me2, c]=(283·8 ± 3·8) kJ mol–1 and ΔH°f[W(η-C5H5)2Me2, c]=(295·6 ± 3·5) kJ mol–1 obtained from measurements of the reaction enthalpies of Mo(η-C5H5)2Me2(c) and W(η-C5H5)2Me2(c) in an aqueous solution of hydrochloric acid.

Lattice potential energies for calcite, aragonite and vaterite: Estimation of the charge distribution on the carbonate ion, the enthalpy of formation, ΔHf°(CO 32−) ( g) and the enthalpy of solvation, ΔHsolv°(CO 32−) ( g) of the gaseous CO 32− ion

The total lattice potential energy, U pot, for the process: CaCO 3(c)⇝ Ca 2+(g)+ CO 3 +−(g) has been computed, as a function of the distributed charge on the anion, for the three pleomorphic forms (calcite, aragonite and vaterite) using recent crystal structure data. The term by term calculations reported represent the most extensive consideration of these systems to date and allow an assignment of the distribution of charge in the CO 3 2− ion corresponding to q o = −0·54 and an estimation of the quadrupole moment of the ion as −6·5 × 10 −26 esu.cm 2. The enthalpy of formation ΔH f °(CO 3 2−) ( g) of the ion is estimated to be −321 kJ mol −1, and the average lattice potential energy of CaCO 3, U pot = 2804 kJ mol −1. The solvation energy of the CO 3 2− ion, ΔH solv°(CO 3 2−) ( g) is estimated to be −1249 kJ mol −1.

ChemInform Abstract: ENTHALPIES OF FORMATION OF ADAMANTANOID COMPOUNDS PART 3, ADAMANTANECARBOXYLIC ACIDS

The standard enthalpies of combustion for adamantane-1- and -2-carboxylic acids have been measured. They are ΔH°c=–(1427.38 ± 0.86) and –(1431.18 ± 0.90) kcal mol–1 respectively. The corresponding standard enthalpies of formation ΔH°f(C11H16O2, c) are –(153.70) and –(149.90) kcal mol–1. The enthalpy of isomerization is compared with the values obtained in similar conformational changes in cyclic molecules.

The enthalpy of decomposition of CF 3NF 2(g) to CF 4(g), N 2(g), and F 2(g)

The enthalpy of formation ΔH f o(CF 3NF 2, g, 298.15 K) has been determined to be − (169.0 ± 0.6) kcal thmol −1 by measurement of its energy of decomposition to CF 4(g), N 2(g), and F 2(g) in a nickel bomb and static calorimeter. A gaseous mixture of C 2N 2(g) and NF 3(g) was used to trigger the reaction. The experimental ΔH f o is compared with that calculated from bond energies, and values of ΔH f o for the series CF x (NF 2)4- x are tabulated.

Thermodynamics of phosgene formation from carbon monoxide and chlorine

From measurements on the gaseous equilibrium COCl 2 = CO + Cl 2 in the temperature range 635 to 760 K, ΔH o(298 K) is calculated to be (25.95 ± 0.10) kcal mol −1. This reaction provides an enthalpy of formation ΔH f o(COCl 2,g,298 K) = −(52.37 ± 0.14) kcal mol −1, which is in excellent agreement with the work of Bodenstein and Plaut.