Thermochemical property

Gamer and Abemethy [3] give the following thermochemical data for the isomers of mononitrotoluene  

HEATS OF COMBUSTION AND HEATS OFFORMATION OF MONONITROTOLUENE ISOMERS 

Isomer Heat of combustion (at constant volume) kcal/mole Heat of formation kcal/mole 

From these data Gamer and Abemethy have calculated the heats of nitration of toluene (Fig. 50 p. 261)  

Nitrotoluene is unaffected by acids but oxidized by strong alkalis (e.g. NaOH), dibenzyl Mid stilbene derivatives being formed (Bender Mid Schultz [4], Fischer and Hepp [5]). Intensely coloured substances appeM transiently, to which the 

The specific heat of nitroglycerine was determined by NauckhofiT [18] as 0.356 cal/g and that of the crystalline substance (stable form) as 0.315 cal/g. For liquid nitroglycerine Belayev [45] published the value 0.4 cal/g. 

The heat of crystallization (freezing) of nitroglycerine has been determined by many authors (Nauckhoff [18], Beckerhinn [44]). The most complete investigations were those performed by Hibbert and Fuller [46] who have established the following data  

the heat of transforming the labile variation into the stable one is 28 cal/g. 

Heat of combustion and heat of formation of nitroglycerine. It has been reported by Rinkenbach [47] that the heat of combustion —A.Hc at constant volume should be 368.4 kcal/mole, which corresponds to 1623 kcal/kg. Thus the heat of formation —Aflf is+85.3 kcal/mole (+374 kcal/kg). 

Values for the heat of formation of nitroglycerine published by other authors are listed below  

A polymer material burns easily, and decorative materials that are made of polymer materials, such as PE, PP, and some natural polymer such as cellulose and so forth frequently pose fire hazards. In addition, a great deal of smoke is produced when some materials such as polypropylene and PVC are burned. Because most packing materials are incombustible, adding packing could reduce the concentration of combustible materials and delay matrix combustion. Shang added the fibrous Mg(OH)2 and globular Al(OH)3 to polypropylene to prepare a composite material. Their result shows that the oxygen index of the composite material with fibrous Mg(OH)2 

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The next higher order of approximation, the first-order approximation, is obtained by estimating molecular properties by the additivity of bond contributions. In the following, we will concentrate on thermochemical properties only. 

Figure 7-1 shows the groups that are obtained for alkanes, and the corresponding notation of these groups as introduced by Benson [Ij. Table 7-2 contains the group contributions to important thermochemical properties of alkanes. Results obtained with these increments and more extensive tables can be obtained from Refs. [1] and [2]. 

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. 

A comparison of the characteristics associated with propellant burning, explosive detonation, and the performance of conventional fuels (see Coal Gas, NATURAL Petroleum) is shown ia Table 1. The most notable difference is the rate at which energy is evolved. The energy Hberated by explosives and propellants depends on the thermochemical properties of the reactants. As a rough rule of thumb, these materials yield about 1000 cm of gas and 4.2 kj (1000 cal) of heat per gram of material. 

I. Barin and O. Knache, Thermochemical Properties of Inorganic Substances Springer Vedag, Berlin, 1973. 

Table 1. Physical and Thermochemical Properties of Oxalic Acid and its Dihydrate...

A. Glassner, The Thermochemical Properties of the Oxides, Fluorides, and Chlorides to 2500 K, Argonne National Laboratory Report ANL-5750, U.S. Government Printing Office, Washington, D.C., 1957. 

Two standard estimation methods for heat of reaction and CART are Chetah 7.2 and NASA CET 89. Chetah Version 7.2 is a computer program capable of predicting both thermochemical properties and certain reactive chemical hazards of pure chemicals, mixtures or reactions. Available from ASTM, Chetah 7.2 uses Benson s method of group additivity to estimate ideal gas heat of formation and heat of decomposition. NASA CET 89 is a computer program that calculates the adiabatic decomposition temperature (maximum attainable temperature in a chemical system) and the equilibrium decomposition products formed at that temperature. It is capable of calculating CART values for any combination of materials, including reactants, products, solvents, etc. Melhem and Shanley (1997) describe the use of CART values in thermal hazard analysis. 

The temperature gradient in the direction of flow can be measured directly with Pt-resistance thermometers, but it is difficult and expensive. When this is small, it is better to calculate from the material balance and thermochemical properties. 

This factor is most important when results are reported for only a subs the entire collection of calculations. For example, some studies re results only for the atomization energies portion of the set. This subs the calculations does not include some difficult molecules presen other thermochemical properties (e.g. PO, whose geometry car challenging to model accurately), and so results for a subset can be i accurate than they would be for the entire set. This effect becomes r pronounced as overall method accuracy increases. Be cautious v general accuracy and applicability conclusions are drawn from such dal... 

Don tpanic This is not to imply that such a method may not be very useful and reliable for modeling other properties of molecular systems. For example, as we ll see in the next subsection, model chemistries that are known to be quite reliable for optimizing geometries can be quite poor at predicting absolute thermochemical properties. 

Polarizabilities and hyperpolarizabUities Thermochemical properties Reaction pathways... 

Table 11.3 Some physical and thermochemical properties of hydrazine...

In addition to the obvious structural information, vibrational spectra can also be obtained from both semi-empirical and ab initio calculations. Computer-generated IR and Raman spectra from ab initio calculations have already proved useful in the analysis of chloroaluminate ionic liquids [19]. Other useful information derived from quantum mechanical calculations include and chemical shifts, quadru-pole coupling constants, thermochemical properties, electron densities, bond energies, ionization potentials and electron affinities. As semiempirical and ab initio methods are improved over time, it is likely that investigators will come to consider theoretical calculations to be a routine procedure. 

A powerful and readily applied method for the estimation of thermochemical properties for gas phase species is that of group additivity developed by Benson and his coworkers15 21-22. The method is based on the observation that the thermochemical properties of a molecule can be represented as a sum of contributions from the individual groups which make up the molecule. The method of defining groups and arriving at group... 

Barin, I., and Knacke, O., Thermochemical Properties of Inorganic Substances, Springer, Berlin (1983)... 

Suleimenov and Ha have used high-level G2 and CBS-Q ab initio methods to study the thermochemical properties of gaseous polysulfanes (H2S , =l-6) [4]. The enthalpy of formation were calculated from atomisation energies and from enthalpies of dehydrogenation reactions such as shown in Eq. (1) ... 

Calculation of thermochemical data using high-quality ab initio electronic structure calculations has been a long-standing goal. However, the availability of supercomputers and new theoretical techniques now allow the calculation of thermochemical properties with chemical accuracy, i.e., AHf to within... 

These results thus show that whereas the flashpoint was only moderately influenced by the compound structure (their chemical functionality but especially their atomic composition and vapour), autoignition temperatures seem to be closely linked to the structural factors that affect the chain. So additivity rules for estimation of AIT should be sought. Every time a chemical or physical property is highly influenced by the structure, chemists tried to establish rules that enable one to reduce a molecule to characteristic groups for which the contribution to the value of this property is known. This was done for instance by Kinney for boiling points and Benson2 for thermochemical properties. 

This equation suggests that the Fe content of tetrahedrite-tennantite positively correlates with that of sphalerite at constant temperature and pressure, indicating Fe and Zn contends of tetrahedrite-tennantite are useful to estimate physicochemical parameters (/sj, /02 etc.) as well as Fe content of sphalerite, although detailed study on thermochemical properties of tennantite-tetrahedrite solid solution is still needed. 

Studies of the Thermochemical Properties of Reactive Intermediates by Mass Spectrometric Methods... 

In molecules with more than one unpaired electron, electron-electron interactions can have a significant role in the stabilization of the system. Bond formation that results from direct overlap is highly favorable and, thus is an overriding consideration in all low-spin polyradicals, even to the extent that the system sometimes adopts a strained, closed-shell state as opposed to a polyradical. In cases in which bonding cannot occur, indirect interactions that are usually insignificant, such as electron exchange and spin-polarization, can have significant impact. The presence of these interactions is often reflected in the thermochemical properties. 

Significant progress in experimental techniques has been made in the time since Lossing s initial reports. In addition to technical improvements in the experimental methods that have been used, there has also been creative development of new strategies for measuring thermochemical properties of a wider range of targets. 

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