Thermochemical sources

Hydrogen from thermochemical sources (hydrogen without carbon emission)... 

Computer-assisted thermochemistry is a tool that can be applied in many fields today. In particular, with the aid of reliable thermochemical source data and appropriate application software, optimum operating tempera tures, reacting amounts and/or gas pressures necessary to obtain a product of the required purity can be calculated. Costly and time-consuming experimental work can thereby be reduced considerably [1]. 

The primary thermochemical source for inorganic and some small organic compounds is Wagman,... 

Black Powder. Black powder is mainly used as an igniter for nitrocellulose gun propellant, and to some extent in safety blasting fuse, delay fuses, and in firecrackers. Potassium nitrate black powder (74 wt %, 15.6 wt % carbon, 10.4 wt % sulfur) is used for military appHcations. The slower-burning, less cosdy, and more hygroscopic sodium nitrate black powder (71.0 wt %, 16.5 wt % carbon, 12.5 wt % sulfur) is used industrially. The reaction products of black powder are complex (Table 12) and change with the conditions of initia tion, confinement, and density. The reported thermochemical and performance characteristics vary greatly and depend on the source of material, its physical form, and the method of determination. Typical values are Hsted in Table 13. 

Heat Capacity, C° Heat capacity is defined as the amount of energy required to change the temperature of a unit mass or mole one degree typical units are J/kg-K or J/kmol-K. There are many sources of ideal gas heat capacities in the hterature e.g., Daubert et al.,"" Daubert and Danner,JANAF thermochemical tables,TRC thermodynamic tables,and Stull et al. If C" values are not in the preceding sources, there are several estimation techniques that require only the molecular structure. The methods of Thinh et al. and Benson et al. " are the most accurate but are also somewhat complicated to use. The equation of Harrison and Seaton " for C" between 300 and 1500 K is almost as accurate and easy to use ... 

Ideal gas absolute entropies of many compounds may be found in Daubert et al.,"" Daubert and Danner," JANAF Thermochemical Tables,TRC Thermodynamic Tables,and Stull et al. ° Otherwise, the estimation method of Benson et al. " is reasonably accurate, with average errors of 1-2 J/mol K. Elemental standard-state absolute entropies may be found in Cox et al." Values from this source for some common elements are listed in Table 2-389. ASjoqs may also be calculated from Eq. (2-52) if values for AHjoqs and AGJoqs are known. 

You have seen that measurements of heats of reaction, such as heats of combustion, can provide quantitative information concerning the relative stability of constitutional isomers (Section 2.18) and stereoisomers (Section 3.11). The box in Section 2.18 described how heats of reaction can be manipulated arithmetically to generate heats of formation (AHf) for many molecules. The following material shows how two different sources of thermochemical information, heats of formation and bond dissociation energies (see Table 4.3), can reveal whether a particular reaction is exothermic or endothermic and by how much. 

Non-electrolytic sources of hydrogen have also been studied. The chemical problem is how to transfer the correct amount of free energy to a water molecule in order to decompose it. In the last few years about I0(X)0 such thermochemical water-splitting cycles have been identified, most of them with the help of computers, though it is significant that the most promising ones were discovered first by the intuition of chemists. 

Sources of thermochemical data for such calculations are Vol 7, H38 Lff Heat Effects — Data for Common Explosives NBS Circular 500 (Ref 39a) Cox Pilcher (Ref 89) and the studies of Rhodes Nelson (Ref 24b) and McKinley Brown (Ref 28a) on mixed acids As an example of such a calculation we will compute the heat evolution and temp rise occurring during the mixed acid nitration of glycerol to NG. We will assume that a typical 50/50 nitric acid/sulfuric acid MA is used and that the MA/glycerol ratio is 5/1. Further assumptions are that all the glycerol is converted to NG, and that the heats of soln of NG in die. spent acid, and of spent acid in the NG, are negligibly small (cf discussion of these effects by the writer in Ref 51). The net reaction is then ... 

The thermochemical data for the sulfoxides, sulfones, sulfites and sulfates, derived from calorimetric measurements, are given in Tables 1-5. All entries in the tables were checked by examination of the original sources. Where available, data are given for the gas phase and either the liquid (lq) or solid (c) phase. Preference was given to gas and liquid phase data. 

The needed thermochemistry for many thousands of molecules is available from standard sources such as the JANAF tables. " Polynomial fits of this data in the form required by our kinetics software are also available. However, experimental thermochemical data is often lacking for many of the intermediate species that should be included in a detailed kinetics mechanism. Standard methods have been developed for estimating these properties, discussed in detail by Benson. ... 

The data in this appendix have been compiled from a number of sources. Nearly all of the critical property data are taken from Appendix A of The Properties of Gases and Liquids, Second Edition, by R. C. Reid and T. K. Sherwood, copyright 1966, McGraw-Hill Book Company. They are used with the permission of McGraw-Hill Book Company. Most of the thermochemical data (AG°, AH°f, and S°) were obtained from the following sources. 

The procedure of Lifson and Warshel leads to so-called consistent force fields (OFF) and operates as follows First a set of reliable experimental data, as many as possible (or feasible), is collected from a large set of molecules which belong to a family of molecules of interest. These data comprise, for instance, vibrational properties (Section 3.3.), structural quantities, thermochemical measurements, and crystal properties (heats of sublimation, lattice constants, lattice vibrations). We restrict our discussion to the first three kinds of experimental observation. All data used for the optimisation process are calculated and the differences between observed and calculated quantities evaluated. Subsequently the sum of the squares of these differences is minimised in an iterative process under variation of the potential constants. The ultimately resulting values for the potential constants are the best possible within the data set and analytical form of the chosen force field. Starting values of the potential constants for the least-squares process can be derived from the same sources as mentioned in connection with trial-and-error procedures. 

To make contact with atomic theories of the binding of interstitial hydrogen in silicon, and to extrapolate the solubility to lower temperatures, some thermodynamic analysis of these data is needed a convenient procedure is that of Johnson, etal. (1986). As we have seen in Section II. l,Eqs. (2) et seq., the equilibrium concentration of any interstitial species is determined by the concentration of possible sites for this species, the vibrational partition function for each occupied site, and the difference between the chemical potential p, of the hydrogen and the ground state energy E0 on this type of site. In equilibrium with external H2 gas, /x is accurately known from thermochemical tables for the latter. A convenient source is the... 

Unless otherwise said, our preferred sources for enthalpies of formation of hydrocarbons are Reference 8 by Roth and his coworkers, and J. B. Pedley, R. D. Naylor and S. P. Kirby, Thermochemical Data of Organic Compounds (2nd ed.), Chapman Hall, New York, 1986. In this chapter these two sources will be referred to as Roth and Pedley , respectively, with due apologies to their coworkers. We will likewise also occasionally take enthalpies of fusion from either E. S. Domalski, W. H. Evans and E. D. Hearing, Heat Capacities and Entropies of Organic Compounds in the Condensed Phase , J. Phys. Chem Ref. Data, 13, 1984, Supplement 1, or E. S. Domalski and E. D. Hearing, J. Phys. Chem Ref. Data, 19, 881 (1990), and refer to either work as Domalski . 

CO)4FeSOOH- + C02. Squires128 had previously measured the bond strength of S02-OH- to be 61.9 kcal/mol, and calculated the bond strength of Fe(CO)5-OH- to be 60.3 kcal/mol. Combined with the heats of formation of Fe(C05) and OH-, they calculated A//f of Fe(CO)4COOH- = -267 kcal/mol. The thermochemical data of the relevant species involved in the catalysis, tabulated from numerous sources, are shown in Table 17. 

To convert these feedstocks into useful chemicals, mainly fermentation, chemical modification or thermochemical methods were applied. However, these processes were later abandoned in favor of the more economic and efficient processes based on fossil resources, in particular oil. Easier transport and more stable chemical composition (biomass feedstocks are highly diverse, depending on the source) are two relevant additional factors in favor of fossil fuels. Therefore, although the concept of biorefinery is attractive, there are several barriers to economically feasible. 

The choice of a given database as source of auxiliary values may not be straightforward, even for a thermochemist. Consistency is a very important criterion, but factors such as the publication year, the assignment of an uncertainty to each value, and even the scientific reputation of the authors or the origin of the database matter. For instance, it would not be sensible to use the old NBS Circular 500 [22] when the NBS Tables of Chemical Thermodynamic Properties [17], published in 1982, is available. If we need a value for the standard enthalpy of formation of an organic compound, such as ethanol, we will probably prefer Pedley s Thermodynamic Data and Structures of Organic Compounds [15], published in 1994, which reports the error bars. Finally, if we are looking for the standard enthalpy of formation of any particular substance, we should first check whether it is included in CODATA Key Values for Thermodynamics [16] or in the very recent Active Thermochemical Tables [23,24],... 

Mass spectrometric measurements coupled with solution thermochemical results are the sources of solvation enthalpy values for anions and cations. These data are related to the lattice energy, which is a parameter used to assess the ionic character of solids and predict their standard enthalpies of formation. An introduction to that... 

Kinetic studies in solution and in the gas phase have been playing an increasingly important role as a source of thermochemical data (see examples in chapter 15). Here we discuss how to relate thermochemical and kinetic information by approaching the subject as we did in the previous chapter by highlighting important practical issues and reducing to a minimum the description of theoretical models. In other words, the present chapter also relies on the material usually covered at the undergraduate level [1]. Further details can be found in more specialized books [55-59],... 

The experimental methods designed to investigate the energetics of gas-phase ions have been another important source of thermochemical data, particularly throughout the past two or three decades [9,10]. In this chapter, we discuss the main quantities that are measured experimentally and lead to reaction enthalpy values. 

The thermochemical study of photochemical or photochemically activated processes is not amenable to most of the calorimeters described in this book, simply because they do not include a suitable radiation source or the necessary auxiliary equipment to monitor the electromagnetic energy absorbed by the reaction mixture. However, it is not hard to conceive how a calorimeter from any of the classes mentioned in chapter 6 (adiabatic, isoperibol, or heat flow) could be modified to accommodate the necessary hardware and be transformed into a photocalorimeter. 

This is, in our opinion, the primary source of thermochemical values and therefore it should be the starting point of all the other databases. The selections have been made by the Task Group on Key Values for Thermodynamics appointed in 1968 by the Committee on Data for Science and Technology (CODATA) of the International Council of Scientific Unions. Unfortunately, the number of species for which data are recommended in the final report is rather small ( 150). 

This has been, for many years, the main source of standard enthalpies of formation of neutral organic compounds. It is a classic work on thermochemistry and has set a standard for thermochemical databases. Superseded by Pedley s 1994 compilation [26]. 

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