Thermochemical data

The thermochemical data for the product species are critical in the calculation of propellant performance. The methods of statistical thermodynamics have provided a reliable technique of establishing most of the thermochemical data required for propellant performance calculations. Again, the JANAF Thermochemical Tables (18) represent an extensive and widely used compilation of these data. 

The reader is assumed to know the principles of chemical thermodynamics, and how to use thermodynamic tables. The present nomenclature in thermochemistry based on the recent lUPAC recommendations [5] is different from that used in older publications, but the symbols used in mathematical equations remain unchanged. A chemical reaction 

The Gibbs energy G is a thermodynamic function, i.e. it is unequivocally defined by the state of the system p, T, and the composition. In other words for a cycle of processes which ends at the initial state AG=0. The Gibbs energy of the entire system (an extensive quantity) can be split into a sum of contributions of particular species i. 

Let us consider the following cyclic process under isothermal and isobaric conditions with all the reactants in their standard states  

It is not possible to calculate the absolute value of Gibbs energy (Eqs (2.5) and (2.6) without certain convention. Let us introduce another thermodynamic function, namely, enthalpy H (the heat produced or consumed, that can be measured calorimetrically). For elements in their most stable form 

The absolute entropy of a solid at 298.15 K (assuming that there is no phase transition between 0 and 298.15 K) can be calculated from the following equation 

RTILs with BF4, PFs, and OCSO4 anions up to 373 K and 200 MPa. The resulting isothermal compressibilities Kt increased in this order of salts from 0.4 to 0.5 GPa at ambient pressure and diminished at increasing pressures. The free, compressible, volumes at 313 K and ambient pressure were 7.4 %, 6.7 %, and 7.6 % respectively. 

Microscopic ionic volumes of RTILs, the sums of the constituent 20 cations and 20 anions Vj = v+ + v, were calculated by several theoretical methods according to Preiss et al. [49] and compared with the crystal volumes obtained from x-ray diffraction (Table 2.4). It was then shown that several physical properties were linear with these microscopic volumes the molar volume V, the isobaric expansibility ap, the molar heat capacity Cp, the (logarithm of) the viscosity In , and the (logarithm of) the molar conductivity InA all these obey the relation a + bv.  

A perturbed hard sphere equation of state (PHS-EoS) was used by Hosseini et al. [50, 51] to model the volumetric properties of RTILs. This EoS has the form  

High pressure densities of imidazoUum-based RTILs were modeled by Machida et al. [54] up to 200 MPa by means of the Sanchez-Lascombe SL-EoS (modified by allowance for the temperature dependence of the interaction energy) with six substance-dependent parameters. High pressure densities of phosphonium RTILs were modeled by Tome et al. [55] up to 45 MPa. 

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To become familiar with the estimation of thermochemical data... 

All three schemes, the Benson, the Laidler, and the Allen scheme, use four structure contributions for the estimation of thermochemical data of alkanes. As might be guessed, they are numerically equivalent all three schemes provide the same accuracy. This is shown below by Eqs. (7)-(10) for the interconversion of the various contributions. 

Any one of these additivity schemes can be used for the estimation of a variety of thermochemical molecular data, most prominently for heats of formation, with high accuracy [13]. A variety of compilations of thermochemical data are available [14-16]. A computer program based on Allen s scheme has been developed [17, 18] and is included in the PETRA package of programs [19]. 

D. Cox, G. Pilcher, Thermochemistry of Organic and Organometallic Compounds, Aademic Press, London, 1970. J. B. Pedley, R. D. Naylor, S. P. Kirby, Thermochemical Data of Organic Compounds, 2nd edition. Chapman and Hall, London, 1986. 

The heats of formation of most organic com pounds are derived from heats of reaction by arith metic manipulations similar to that shown Chemists find a table of AH values to be convenient because it replaces many separate tables of AH° values for indi vidual reaction types and permits AH° to be calcu lated for any reaction real or imaginary for which the heats of formation of reactants and products are available It is more appropriate for our purposes however to connect thermochemical data to chemi cal processes as directly as possible and therefore we will cite heats of particular reactions such as heats of combustion and heats of hydrogenation rather than heats of formation... 

The activation energy for ro tation about a typical carbon-carbon double bond IS very high—on the order of 250 kj/mol (about 60 kcal/ mol) This quantity may be taken as a measure of the ir bond contribution to the to tal C=C bond strength of 605 kJ/mol (144 5 kcal/mol) in ethylene and compares closely with the value esti mated by manipulation of thermochemical data on page 191... 

References D. D. Wagman, et ah, The NBS Tables of Chemical Thermodynamic Properties, in J. Phys. Chem. Ref. Data, 11 2,1982 M. W. Chase, et ah, JANAF Thermochemical Tables, 3rd ed., American Chemical Society and the American Institute of Physics, 1986 (supplements to JANAF appear in J. Phys. Chem. Ref. Data) Thermodynamic Research Center, TRC Thermodynamic Tables, Texas A M University, College Station, Texas I. Barin and O. Knacke, Thermochemical Properties of Inorganic Substances, Springer-Verlag, Berlin, 1973 J. B. Pedley, R. D. Naylor, and S. P. Kirby, Thermochemical Data of Organic Compounds, 2nd ed.. Chapman and Hall, London, 1986 V. Majer and V. Svoboda, Enthalpies of Vaporization of Organic Compounds, International Union of Pure and Applied Chemistry, Chemical Data Series No. 32, Blackwell, Oxford, 1985. 

Table 17. Thermochemical Data for the Decomposition of Ammonium Nitrate...

Alkaline-Earth Metal Hydrides. Table 2 gives thermochemical data of alkaline-earth metal hydrides. AH form orthorhombic crystals. 

T. E. Dergazarian and co-workers, Jd I fd E Thermochemical Data, Dow Chemical Co., Midland, Mich., 1961. Thermochemical data from these tables were used whenever possible. 

D. R. hide andH. V. Kehiaian, CEC Handbook of Thermophjsical and Thermochemical Data, CRC Press Inc., Boca Raton, Fla., 1994. 

Thermochemical Data. Equilibrium considerations significantly limit alcohol yield at low pressures in the vapor-phase process (116). Consequently, conditions controlling equilibrium constants have been determined and give the following relation, where Tis in K (116,117) ... 

Pyrotechnics is based on the estabflshed principles of thermochemistry and the more general science of thermodynamics. There has been Httle work done on the kinetics of pyrotechnic reactions, largely due to the numerous chemical and nonchemical factors that affect the bum rate of a pyrotechnic mixture. Information on the fundamentals of pyrotechnics have been pubflshed in Russian (1) and English (2—6). Thermochemical data that ate useful in determining the energy outputs anticipated from pyrotechnic mixtures are contained in general chemical handbooks and more specialized pubHcations (7-9). 

Table 2. Thermochemical Data for the Formation of Titanium Compounds ...

Boron Monoxide and Dioxide. High temperature vapor phases of BO, B2O3, and BO2 have been the subject of a number of spectroscopic and mass spectrometric studies aimed at developiag theories of bonding, electronic stmctures, and thermochemical data (1,34). Values for the principal thermodynamic functions have been calculated and compiled for these gases (35). 

A number of reviews have appeared covering the various aspects of borate glasses. The stmcture, physical properties, thermochemistry, reactions, phase equihbria, and electrical properties of alkah borate melts and glasses have been presented (73). The apphcation of x-ray diffraction, nmr, Raman scattering, in spectroscopy, and esr to stmctural analysis is available (26). Phase-equihbrium diagrams for a large number of anhydrous borate systems are included in a compilation (145), and thermochemical data on the anhydrous alkah metal borates have been compiled (17). 

Boron tnhahdes, BX, are trigonal planar molecules which are sp hybridized. The X—B—X angles are 120°. Important physical and thermochemical data are presented in Table 1 (8—14). Additional thermodynamic and spectroscopic data may be found in the hterature (1 5). 

Boron subhaHdes are binary compounds of boron and the halogens, where the atomic ratio of halogen to boron is less than 3. The boron monohaUdes, BCl, [20583-55-5] bromoborane(l) [19961-29-6] BBr, and iodoborane(l) [13842-56-3] BI, are unstable species that have been observed spectroscopicaHy when the respective ttihaUdes were subjected to a discharge (5). Boron dihaUde radicals have been studied, and stmctural and thermochemical data for these species ( BX2) have been deduced (5). 

Thermodynamic calculations for reactions forming carbon disulfide from the elements are compHcated by the existence of several known molecular species of sulfur vapor (23,24). Thermochemical data have been reported (12). Although carbon disulfide is thermodynamically unstable at room temperature, the equiHbtium constant of formation increases with temperature and reaches a maximum corresponding to 91% conversion to carbon disulfide at about 700°C. Carbon disulfide decomposes extremely slowly at room temperature in the absence of oxidizing agents. 

The physical and thermodynamic properties of carbon monoxide are well documented in a number of excellent summaries (1 8). The thermochemical data cited here are drawn predominantly from references 1—3 physical property data from reference 5. A summary of particularly useful physical constants is presented in Table 1. 

Interatomic distances calculated from the detailed analysis of rotational fine structure of the UV spectrum of pyrazine are in close agreement with those observed in (7) and (8), with the calculated bond lengths for C—C of 1.395, C—N 1.341 and C—H 1.085 A (60DIS(20)4291). Thermochemical data have provided a figure of 75 kJ moP for the delocalization energy of the pyrazine ring (B-67MI21400). 

A modified definition of resonance energy has been introduced by Dewar (66T(S8)75, 69JA6321) in which the reference point is the corresponding open-chain polyene. In principle this overcomes the difficulties inherent in comparing observed stability with that of an idealized molecule with pure single and double bonds, as thermochemical data for the reference acyclic polyenes are capable of direct experimental determination. In practice, as the required data were not available, recourse was made to theoretical calculations using a semiempirical SCF-MO method. The pertinent Dewar Resonance Energies are listed in Table 30. 

Two now classical papers 61MI40400, 62JCS2927) contain almost all the experimental thermochemical data on pyrazole and indazole. Heats of combustion determined by Zimmerman (61MI40400) have been used by Dewar to calculate the heats of atomization (Table 25) (69JA796). Quantum mechanical calculations, carried out by Dewar (69JA796) or Olivella 81JHC1189), gave accurate empirical values. 

Table 25 Experimental and Calculated Thermochemical Data of Pyrazole and Indazole (kJ mol )...

The absorption wavelengtlrs quoted here are for the complete dissociation of these molecules to the atoms in their ground state. The thermochemical data also show that a temperature of nearly 4000 K is requhed before the atomic oxygen concentration is equal to that of molecular oxygen, and almost 7000 K for the nitrogen atom population to be equal to the molecular nitrogen concentration, at one atmosphere pressure. 

Hillert, M. (1980) in Conference on the Industrial Use of Thermochemical Data, ed. Barry, T. (Chemical Society, London) p. 1. 

Examine the following thermochemical data pertaining to hydrogenation of unsaturated eight-membered ring hydrocarbons to give cyclooctane ... 

Because these various quantities are characteristics of the reactants and products but are independent of the reaction path, they cannot provide insight into mechanisms. Information about AG, AH, and AS does, however, indicate the feasibility of any specific reaction. The enthalpy change of a given reaction can be estimated from tabulated thermochemical data or from bond-energy data such as those in Table 1.3 (p. 14) The exan le below illustrates the use of bond-energy data for estimating the enthalpy of a reaction. 

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