Thermodynamics calculating heats formation

Equilibrium vapor pressures were measured in this study by means of a mass spectrometer/target collection apparatus. Analysis of the temperature dependence of the pressure of each intermetallic yielded heats and entropies of sublimation. Combination of these measured values with corresponding parameters for sublimation of elemental Pu enabled calculation of thermodynamic properties of formation of each condensed phase. Previ ly reported results on the subornation of the PuRu phase and the Pu-Pt and Pu-Ru systems are correlated with current research on the PuOs and Pulr compounds. Thermodynamic properties determined for these Pu-intermetallics are compared to analogous parameters of other actinide compounds in order to establish bonding trends and to test theoretical predictions. 

Quantum-chemical calculations (AMI, PM3) have been carried out in order to investigate the thermodynamic behavior of the possible equilibrium between variously substituted 6-azidotetrazolo[l,5-A pyridazine 11 and the bis-tetrazole 12 <2005JST65> (Scheme 2). From the calculated heat of formation, the authors concluded that this value is consistently lower for the azide tautomers 11 than for the corresponding tetrazoles 12 on average by 20kcalmol 1 and, thus, the azide isomers- in full accordance with the experimental observations - are more stable than the ring-closed fused tetrazoles. 

For thermodynamic calculation of equilibria useful in petroleum science, combustion data of extreme accuracy are required because the heats of formation of water and carbon dioxide are large in comparison with those in the hydrocarbons. Great accuracy is also required of the specific heat data for the calculation of free energy or entropy. Much care must be exercised in selecting values from the literature for these purposes, since many of those available were determined before the development of modem calorimetric techniques. 

The procedure for calculating standard formation properties of species at zero ionic strength from measurements of apparent equilibrium constants is discussed in the next chapter. The future of the thermodynamics of species in aqueous solutions depends largely on the use of enzyme-catalyzed reactions. The reason that more complicated ions in aqueous solutions were not included in the NBS Tables (1992) is that it is difficult to determine equilibrium constants in systems where a number of reactions occur simultaneously. Since many enzymes catalyze clean-cut reactions, they make it possible to determine apparent equilibrium constants and heats of reaction between very complicated organic reactants that could not have been studied classically. 

The heat of explosion may be both theoretically calculated and experimentally determined. The calculated value is the difference between the energies of formation of the explosive components (or of the explosive itself if chemically homogeneous) and the energies of formation of the explosion products (for more details -> Thermodynamic Calculation of Decomposition Reactions). The advantage of the calculation method is that the results are reproducible if based on the same energies of formation and if the calculations are all conducted by the same method this is often done with the aid of a computer. 

If a reaction in a mixture of solids is accompanied by the formation of gas or fluid phases (melts, solutions), solid solutions, or by the generation of defects, then, for a more strict thermodynamic forecast, it is necessary to take into account the changes of entropy and specific heat capacity during phase transitions of the components (melting, vaporization, dissolution), changes of volume and other parameters. If these factors are not taken into account, one can come across the contradictions between experimental data and thermodynamic calculations. 

Thermodynamic quantities (heat of formation and combustion, free energy, heat capacity, entropies, heats of fusion and vaporization) for thietane have been obtained or calculated and the strain energy has been assessed (18.9-19.6kcal/mol). ° ° Thietane is about as strained as thiirane and is much more strained than thiacyclopentane (about 1.0-2.0kcal/mole) and less strained than cyclobutane (26.1 kcal/mole). The heat of formation in the liquid state, A// , is 5.77 or 6.04 kcal/mole. ... 

The enthalpies of formation of biomass are quite useful for thermodynamic calculations. The heats of specific reactions that utilize biomass feedstocks can be estimated from the standard enthalpies of formation at 298 K of the combustion products (in kcal/g-mol CO, -94.05 liquid H O, —68.37 NO2, 8.09 SO2, —70.95), the elemental analyses of the biomass being examined, and its HHV. The enthalpy of formation of a particular biomass sample is equal to the sum of the heats of formation of the products of combustion... 

The standard free energy of formation, AG°, of caesium monoxide has been calculated from experimental results as -308.42 1.18 kcal mol-1. To permit practical thermodynamic calculations to be made at higher temperatures, experimentally determined heat capacities at 5—350 K have been extrapolated to 763 K, the m.p. of Cs20, and a table of extrapolated thermodynamic functions, including AG°, is now available up to 763 K.162... 

Heat of Reaction The heat of reaction is defined as the energy absorbed by the system when the products after reaction are restored to the same temperature as the reactants. The pressure must also be specified for a complete definition of the thermodynamic states of the products and reactants. If the same pressure is chosen for both, the heat of reaction is equal to the enthalpy change this is the customary definition of the heat of reaction. The heat of any reaction can be calculated by combining heats of formation or heats of combustion of the products and reactants. Thus the basic information necessary for calculating heats of reaction are heats of formation and... 

Most meteorites are chondrites, so-called because almost all contain spherical mm- to cm-sized chondrules or their fragments early in the Solar System s history. Cooling rates for some were 1000 C/hr, and 10-100°C/hr for others. Rapid heating and cooling are easily done in the laboratory but difficult on a Solar System scale. Yet, large volumes of chondrules must have existed in the Solar System because chondrites are numerous (Table I). Chondrites (and many achondrites) date to the Solar System s formation - indeed provide chronometers for it and represent accumulated primary nebular condensate and accretionary products. Some condensate formed from the hot nebula as mm-sized Ca- and Al-rich inclusions (CAI), mineral aggregates predicted as vapor-deposition products by thermodynamic calculations. These CAI, found mainly in chondrites rich in carbonaceous (organic) material exhibit many... 

Finally, for C-J temperatures above the boiling point of the metal, consideration should be given to the possible existence of distinct species in the gas phase. To include them as components in the assumed set of detonation gases requires knowledge of their molecular geometry and ideal-gas thermodynamic properties (e.g., heat capacity as a function of temperature and heat and entropy of formation). In the absence of such data, it is possible to predict the molecular geometry and thermodynamic properties via quantum-chemical and statistical-thermodynamic calculations, respectively, or to estimate them by analogy with known related molecules. 

However, to use thermodynamically calculated results for the interpretation requires the consideration of the materials microstructure, specific crystallization behavior and the kinetics of phase formation and phase reaction. This is true especially for the interpretation of dynamic thermal analysis experiments (e.g. DTA, TG). Moreover, heat treatments (e.g. thermolysis) are often carried out in an inert atmosphere and evaporating gaseous species are continuously removed by flowing gas atmospheres (inert or reactive). This effect deeply... 

Thermodynamic Data of Formation. The standard enthalpy of formation of gaseous PH3, fH298 = 5.4 1.7 kJ/mol, was calculated from the heats of the explosive decomposition of PH3/SbH3 mixtures with white phosphorus as the reference state and is the recommended value different experimental values are given in Phosphor C, 1965, pp. 10/1. The experimentally determined value yields AfG29s=13.4 and AfHo=13.39 kJ/mol [27]. Calculations from molecular constants with standard methods yielded thermodynamic data of formation and the equilibrium constant for the formation of PH3 as an ideal gas the reference states used were crystalline a white phosphorus (0 to 195 K), crystalline p white phosphorus (195 to 317 K), the melt (317 to 1180 K), and an ideal P2 gas at higher temperatures. Selected results are as follows [28] ... 

According to the thermodynamic calculation, it is possible to make a conclusion that all presented SHS-Az systems can be self-igniting. Moreover, combusting temperatures and reaction heat are sufficient for base products formation. The presence of the active nitrogen and fuel elements without oxide layer is a supposition for the positive result of nitride synthesis by azide technology. At that, formation reactions of some nitrides are carried out in the gas-vapor phase, that allows to get nano-sized nitride powders. 

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