Hydrocarbons heat of formation

Table CXXIX. Heats of Formation of Molecular Compounds Hustrate the order of maRni-between Trinitrobeniem and Hydrocarbons heats of formation...

Hydrocarbon Heat of formation heals Hydrocarbon Heat of formation heals... 

Hydrocaibons with branched chain Heat of formation of isomet ic hydrocarbon kcals Corresponding normal hydrocarbon Heat of formation of notmal hydrocarbon kcals Difference kcals... 

Hydrocarbon Heat of formation keals Hydrocarbon Heat of formation keals... 

Hydrocarbon heats of formation calculated at these levels appear, then, to reproduce experimental values very well and can be useful in assessing the reliability of doubtful experimental energies, thus setting the stage for application of these methods to carbocations, where the experimental problems are more difficult. 

The following data (Table 1) for molecules, including hydrocarbons, strained ring systems, molecules with heteroatoms, radicals, and ions comes from a review by Stewart.For most organic molecules, AMI reports heats of formation accurate to within a few kilocalories per mol. For some molecules (particularly inorganic compounds with several halogens, such asperchloryl fluoride, even the best semi-empirical method fails completely. 

The solubihty of sulfur dichloride ia water is not meaningflil because it reacts rapidly. It is slightly soluble ia aUphatic hydrocarbons and very soluble ia benzene and carbon tetrachloride. The heat of formation is —22 kJ/mol (—5.3 kcal/mol) for the gas at 25°C (138). 

Combustion. The primary reaction carried out in the gas turbine combustion chamber is oxidation of a fuel to release its heat content at constant pressure. Atomized fuel mixed with enough air to form a close-to-stoichiometric mixture is continuously fed into a primary zone. There its heat of formation is released at flame temperatures deterruined by the pressure. The heat content of the fuel is therefore a primary measure of the attainable efficiency of the overall system in terms of fuel consumed per unit of work output. Table 6 fists the net heat content of a number of typical gas turbine fuels. Net rather than gross heat content is a more significant measure because heat of vaporization of the water formed in combustion cannot be recovered in aircraft exhaust. The most desirable gas turbine fuels for use in aircraft, after hydrogen, are hydrocarbons. Fuels that are liquid at normal atmospheric pressure and temperature are the most practical and widely used aircraft fuels kerosene, with a distillation range from 150 to 300 °C, is the best compromise to combine maximum mass —heat content with other desirable properties. For ground turbines, a wide variety of gaseous and heavy fuels are acceptable. 

For values of heats of combustion of large numbers of organic compounds hydrocarbons and others, see Cox, J.D. Pilcher, G. Thermochemistry of Organic and Organometallic Compounds, Academic Press NY, 1970 Domalski, E.S. J. Phys. Chem. Ref. Data, 1972,1, 221. For large numbers of heats of formation values (from which heats of combustion are easily calculated) see Stull, D.R. Westrum Jr., E.F. Sinke, G.C. The Chemical Thermodynamics of Organic Compounds, Wiley NY, 1969. 

Because E -constants for complex groups are obtainable at present only by an empirical procedure82 a corresponding analysis is not possible for aryl-, vinyl-, and other nonflexible a-type radicals. This difficulty was overcome recently by the development of a new set of steric substituent parameters. 9f for front strain phenomena. These constants are defined as the difference in heat of formation for the hydrocarbons 30 and 31. The heats of formation are calculated for this purpose by... 

The adiabatic flame temperatures presented in Table B1 were calculated using the CEA code of Gordon and McBride (http //www.grc.nasa.gov/WWW/CEAWeb/) described in Appendix I for a constant pressure and constant enthalpy condition (initial temperature of 298 K and pressure of 1 atm). The mixture for each fuel is stoichiometric with air. The heats of formation for the hydrocarbons are from the CRC Handbook of Chemistry and Physics (82nd edition, CRC Press, Inc., Boca Raton, EL, 2002). 

Previously used force fields listed in Table 1 reproduce the heat of formation for hydrocarbons with about 50% greater standard deviation than is found in the errors of experimental values. The Wertz-Allinger force field is close to an experimental error-limited force... 

Standard Deviations in Heats of Formation for Hydrocarbons for a Standard Set of Compounds... 

---