Combustion, standard heat

Clausius/Clapeyron equation, 182 Coefficient of performance, 275-279, 282-283 Combustion, standard heat of, 123 Compressibility, isothermal, 58-59, 171-172 Compressibility factor, 62-63, 176 generalized correlations for, 85-96 for mixtures, 471-472, 476-477 Compression, in flow processes, 234-241 Conservation of energy, 12-17, 212-217 (See also First law of thermodynamics) Consistency, of VLE data, 355-357 Continuity equation, 211 Control volume, 210-211, 548-550 Conversion factors, table of, 570 Corresponding states correlations, 87-92, 189-199, 334-343 theorem of, 86... 

Explain in your own words the concepts of heat of reaction exothermic and endothermic reactions heat of formation combustion heat of combustion standard heats of formation, combustion, and reaction heating value of a fuel adiabatic flame temperature ignition temperature ignition lag lower and upper flammability limits and flash point of a fuel a flame blue and yellow flames flashback and detonation. 

Usually all of the enthalpies in reaction 2.2 refer to the reactants and products in the ideal gaseous state, and appropriate corrections must be made for a change of state if some of the components are in the liquid or solid state. To appreciate this fact fully, let us consider the combustion of a typical organic compound. Depending on the atoms in the molecule, the final products of combustion would be H2O, CO2, SO2, N2, and HX (where X is a halogen). The heat evolved in such a reaction is called the heat of combustion. Standard heats of combustion are often listed with H2O in the liquid state (i.e., as water) thus a suitable correction must be made to get the values with all of the products in the gaseous state. This is illustrated in Example 2.1. 

The hydrogen content, heat of combustion, specific heat, and thermal conductivity data herein were abstracted from Bureau of Standards MisceUaneous Pubhcation 97, Thermal Propei tie.s of Petroleum Products. These data are widely used, although other correlations have appeared, notably that by Linden and Othmer Chem. Eng. 54[4, 5], April and May, 1947). 

Thus, the standard heat of a reaction is obtained by taking tlie difference between tlic standard heat of formation of tlie products and reactants. Once again, if the standard heat of reaction of formation is negative, as is the case of most combustion reactions, then energy is liberated due to tlie chemical reaction. Energy is absorbed if AH° is positive. 

The material in this section is divided into three parts. The first subsection deals with the general characteristics of chemical substances. The second subsection is concerned with the chemistry of petroleum it contains a brief review of the nature, composition, and chemical constituents of crude oil and natural gases. The final subsection touches upon selected topics in physical chemistry, including ideal gas behavior, the phase rule and its applications, physical properties of pure substances, ideal solution behavior in binary and multicomponent systems, standard heats of reaction, and combustion of fuels. Examples are provided to illustrate fundamental ideas and principles. Nevertheless, the reader is urged to refer to the recommended bibliography [47-52] or other standard textbooks to obtain a clearer understanding of the subject material. Topics not covered here owing to limitations of space may be readily found in appropriate technical literature. 

The standard heat of combustion (ziH") of a chemical substance (usually an organic compound) is the same as the standard heat of reaction for complete oxidation of 1 mole of the substance in pure oxygen to yield COj(g) and HjO(f) as products. A reference state of 25°C and 1 atm is assumed in quoting standard heats of combustion in cal/g-mole. The value of AH" is always negative because combustion is an exothermic reaction. Note that the standard heats of combustion for carbon and hydrogen are the same as the heats of formation for CO,(g) and HjO(f), respectively. 

Find the standard heat of formation of benzene (() given the following heats of combustion data (in kcal/g-mole) at 1 atm and 25°C ... 

The heat of combustion of a compound — AH° is the standard heat of reaction for complete combustion of the compound with oxygen. Heats of combustion are relatively easy to determine experimentally. The heats of other reactions can be easily calculated from the heats of combustion of the reactants and products. 

Heats of reaction can be calculated from the heats of formation of the reactants and products, as described in Chapter 3, Section 3.11. Values of the standard heats of formation for the more common chemicals are given in various handbooks see also Appendix C. A useful source of data on heats of formation, and combustion, is the critical review of the literature by Domalski (1972). 

To calculate the heat release from combustion and the temperature of the products of combustion, the thermodynamic path shown in Figure 15.20 can be followed18. The actual combustion process goes from reactants at temperature T to products at temperature T2. However, it is more convenient to follow the alternative path from reactants at temperature T that are initially cooled (or heated) to standard temperature of 298 K. The combustion reactions are then carried out at a constant temperature of 298 K. Standard heats of combustion are available for this. The products of combustion are then heated from 298 K to the final temperature of 7i. The actual heat of combustion is given by18 ... 

Standard heats of combustion are widely available. Table 15.11 provides a list of some combustion reactions. 

When using data for standard heats of combustion, care should be taken regarding the initial state of the reactants and the final state of the products. If these do not correspond with the conditions for the actual combustion, then errors can arise. Note in Table 15.11, the final state of water was... 

Fluid properties can be taken as that of air with or without attention to temperature effects. Because of the large temperature range found in combustion, true property effects with temperature are rarely perfectly taken into account. However, in keeping with standard heat transfer practices of adopting properties at a film temperature, the following are recommended ... 

Extensive tables of standard heats of formation are available, but they are not all at the same reference temperature. The most convenient are the compilations known as the JANAF [1] and NBS Tables [2], both of which use 298 K as the reference temperature. Table 1.1 lists some values of the heat of formation taken from the JANAF Thermochemical Tables. Actual JANAF tables are reproduced in Appendix A. These tables, which represent only a small selection from the JANAF volume, were chosen as those commonly used in combustion and to aid in solving the problem sets throughout this book. Note that, although the developments throughout this book take the reference state as 298 K, the JANAF tables also list A// for all temperatures. 

Here, v is the muzzle velocity of the projectile in m s-1, m and M are the mass of the propellant and projectile in grams, respectively, and Q is the amount of chemical energy released by the combustion of the propellants in J g-1. The value for Q (also known as the Heat of Deflagration ) can be calculated from the standard heats of formation as shown in Equation 8.2. 

Methyl ferf-butyl ether (MTBE), C5H12O, a gasoline additive used to boost octane ratings, has AH°f = —313.6 kj/mol. Write a balanced equation for its combustion reaction, and calculate its standard heat of combustion in kilojoules. 

Thermochemical data on expls are well documented in this Encycl and elsewhere. The heats of combustion and of expln are listed in Vol 4, D380 to D-3 81. The Standard Heats of Formation and the Heats of Detonation of common expls are found in Vol 7, H41 to H43, those of nitroalkanes in Vol 7, H54. The heats of phase change are tabulated in Vol 7, H44, and the thermal conductivities and specific heats in Vol 7, H45 to H46. The Free Energy Functions of the Detonation Products were listed in Vol 8, P388. A discussion of the thermochemical and detonation characteristics of liq expls are tabulated in Vol 7, L26-L to L34-R. Important... 

Calculate methane standard heat of combustion with water as liquid product CH4 + 202 > C02 +2H20... 

---