Carbon thermodynamic data

When one considers the potential high-energy release on rupture of a carborane unit, together with the thermodynamic stability of combustion products, it is hardly surprising that there is a body of literature that reports on the use of carbo-ranes within propellant compositions. Their use in energetic applications is to be expected when the enthalpy of formation (AH/) data for the products of combustion for boron are compared to those of carbon. Thermodynamic data for the enthalpy of formation of o-carborane and of typical boron and carbon combustion products is shown in Table 4. Measurements of the standard enthalpy of combustion32 for crystalline samples of ortho-carborane show that complete combustion is a highly exothermic reaction, AH = — 8994 KJmol. ... 

Table 2. Thermodynamic Data for Carbon Monoxide (Ideal Gas) b ...

Flame Temperature. The adiabatic flame temperature, or theoretical flame temperature, is the maximum temperature attained by the products when the reaction goes to completion and the heat fiberated during the reaction is used to raise the temperature of the products. Flame temperatures, as a function of the equivalence ratio, are usually calculated from thermodynamic data when a fuel is burned adiabaticaHy with air. To calculate the adiabatic flame temperature (AFT) without dissociation, for lean to stoichiometric mixtures, complete combustion is assumed. This implies that the products of combustion contain only carbon dioxide, water, nitrogen, oxygen, and sulfur dioxide. 

The above data are correct to about 20 kJ mole but it will be seen that the general trend among these more covalent bonds does appear to be a decrease in stability from carbon to silicon, i.e. the same way as was found for more ionic bonds in the halides. Thermodynamic data for metallorganic methyl compounds used in the produchon of semiconductor systems are shown in Table 2.3. 

It should be remarked that a detailed study of the elimination of mairganese and silicon from the liquid metal shows that silicon together with some of the mairganese is hrst removed, followed by tire rest of the manganese together with some of the carbon, which is hnally removed together widr half of the sulphur contained in the original liquid. This sequence is in accord with what would be expected from thermodynamic data for the stabilities of dre oxides. 

This paper surveys the field of methanation from fundamentals through commercial application. Thermodynamic data are used to predict the effects of temperature, pressure, number of equilibrium reaction stages, and feed composition on methane yield. Mechanisms and proposed kinetic equations are reviewed. These equations cannot prove any one mechanism however, they give insight on relative catalyst activity and rate-controlling steps. Derivation of kinetic equations from the temperature profile in an adiabatic flow system is illustrated. Various catalysts and their preparation are discussed. Nickel seems best nickel catalysts apparently have active sites with AF 3 kcal which accounts for observed poisoning by sulfur and steam. Carbon laydown is thermodynamically possible in a methanator, but it can be avoided kinetically by proper catalyst selection. Proposed commercial methanation systems are reviewed. 

Reactions 1 and 3 are highly exothermic and therefore have equilibrium constants that decrease rapidly with temperature. Reaction 2 is moderately exothermic, and consequently its equilibrium constant shows a moderate decrease with temperature. Reaction 4 is moderately endothermic, and its equilibrium constant increases with increasing temperature. The relationship between temperature and equilibrium constant for these four reactions is depicted in Figure 1 where carbon is assumed to be graphite. Thermodynamic data were taken from Refs. 1 and 2. 

Little work has been carried out using electrochemical cells to analyze for impurities. Thermodynamic data have been measured for the interaction of nuclear fuels with liquid potassium using cells based on ThOj-YjOj electrolytes, so such cells could be used to monitor oxygen. Both the diffusion and electrochemical types of hydrogen and carbon meters should function satisfactorily in liquid potassium. 

A detailed theoretical study of the properties of the redox system FeS/FeS2 was carried out in the Department of Geosciences of SUNY Stony Brook (Schoonen et al., 1999). The authors conclude that the hypothetical reduction of CO2 (by the FeS/FeS2 redox pair) formulated in Wachtershauser s early work, and the carbon fixation cycle on the primeval Earth associated with it, probably could not have occurred. This judgement is made on the basis of a theoretical analysis of thermodynamic data other conditions would naturally have been involved if CO had reacted rather than C02. It is not known whether free CO existed in the hydrosphere, or if so, at what concentrations. 

Experimental and estimated thermodynamic data of homoleptic dialkylzinc compounds are listed in Table 3. Like many organometallic compounds, the lower dialkylzincs have a positive enthalpy of formation, and only the incorporation of silicon atoms in the /3-position imparts significant thermodynamic stability. The mean Zn-C bond rupture enthalpies, all of which are quite low, follow a similar trend as the bond lengths in these compounds. Thus, the presence of methyl substituents in the a-position weakens the zinc-carbon bonds, while silyl substituents strengthen them. 

The heats of formation of CH4 and e are well known, but we cannot directly obtain the heat of formation of CH4 from ordinary thermodynamic data. However, we can do this if we apply the so-called equivalent cores approximation6 n> 2a 24 According to this approximation, the hypothetical process in which an electron is transferred from the nucleus of a core-ionized atom to the core hole has an energy which is independent of the chemical environment of the core-ionized atom. For example, in the case of carbon Is holes in CH4 and CO2, it is assumed that the following reactions have the same energy. 

References (20, 22, 23, 24, 29, and 74) comprise the series of Technical Notes 270 from the Chemical Thermodynamics Data Center at the National Bureau of Standards. These give selected values of enthalpies and Gibbs energies of formation and of entropies and heat capacities of pure compounds and of aqueous species in their standard states at 25 °C. They include all inorganic compounds of one and two carbon atoms per molecule. 

The insertion of CO is in many instances thermodynamically unfavourable the thermodynamically most favourable product in hydroformylation and carbonylation reactions of the present type is always the formation of low or high-molecular weight alkanes or alkenes, if chain termination occurs via (3-hydride elimination). The decomposition of 3-pentanone into butane and carbon monoxide shows the thermodynamic data for this reaction under standard conditions. Higher pressures of CO will push the equilibrium somewhat to the left. 

Thermodynamic data will be used to calculate AH as a function of temperature between 298 and 1000 K. AG and K will then be calculated over the same temperature range. Finally, the equilibrium composition of a stoichiometric mixture of carbon monoxide and hydrogen at a temperature of 600 K and a pressure of 300 atm will be obtained. 

Incidentally, I should say that the thermodynamic data on cobalt(III) indicates that it is a hard acid, but just barely so, and one might say borderline. It is a little harder than tetrahedral carbon and alkyl halides. So hydroxide ion in that sense would be expected perhaps to be a good nucleophilic reagent, as hard acids would like hydroxide ion. 

Prom the following thermodynamic data, with the assumptions that the heat capacities of reaction are negligible and that standard conditions (other than temperature) prevail, calculate the temperatures above which (a) carbon monoxide becomes the more stable oxide of carbon, in the presence of excess C (6) carbon is thermodynamically capable of reducing chromia (Cr2Os) to chromium metal (c) carbon might, in principle, be used to reduce rutile to titanium metal and (d) silica (taken to be a-quartz) may be reduced to silicon in a blast furnace. 

Furthermore, Conant originated, or helped originate, several other fundamental aspects of chemistry. He was among the group who applied "C (it was the only isotope of carbon then available) to a trail-blazing study of a metabolic pathway. He and G. B. Kistiakowsky initiated the measurement of the heats of hydrogenation of organic compounds, so as to improve the precision of thermodynamic data relative to those available from heats of... 

The volume of tabular information necessary to record in detail the thermodynamic data for the paraffin hydrocarbons and their mixtures, as was done for steam, is excessive. It appears hopeful that graphical generalizations typified by the work of Edmister (19) will prove adequate for the less rigorous requirements of design, whereas the Benedict equation of state (4) may be employed where precision is necessary. However, the effective application of this equation of state to compounds containing more than four carbon atoms per molecule still awaits the evaluation of the constants. After the composition and specific volume have been established for a particular state, the solution of equations of state to establish enthalpy and entropy is a straightforward process. 

Thermodynamic data on hydrocarbons show that at temperatures above 1300°C. ethylene, acetylene, and carbon are more stable than methane or other saturated hydrocarbons however, although data of this kind will indicate the species likely to be formed at high temperatures, the amounts of unsaturated hydrocarbons and carbon produced will depend on the rates of the reactions involved and on the temperature cycle used. 

The theoretical yields of cyanogen obtained by the reaction of carbon and nitrogen can also be derived from thermodynamic data. At high temperatures cyanogen is partly dissociated into cyanogen radicals, and the following simultaneous equilibria must be considered ... 

Intramolecular rotations in carboxylic and carbonic acid amides have been thoroughly investigated by 1H NMR [108]. The thermodynamic data for rotation in N,N-di-methyltrichloroacetamide as obtained by 1H and 13C 1H NMR agree quite well CH AG294 = 76.5 kJ/mol 13C AG BB = 73.6 kJ/mol) [109]. 

Figure 25.5 Differences in cohesive energies, extracted from thermodynamic data, for carbides of the 3d-, 4d- and 5d-series. These curves show the expected sign of the surface core level shift for (a) carbon and (b) metal levels. See text for details.

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