Heat of reaction calculation

Heat of reaction calculated from product gas composition using heats of formation (50). 

Fig. 3. 49 Effect of KCIO 3 on the heat of reaction calculated by RE1TP-2 (QREITP-2), on the TNO detonation velocity, and on the IMO combustion rate of KCIO 3 /cellulose...

To compare with this method, the heat of reaction calculated by REITP-2 8 9 , the combustion rate at the time of ignition under open conditions 3 3 3 0 in the IMO combustion rate tests 3 0 3 2 > and the combustion rate under conditions of partial enclosure 11 4 in the TNO deflagration tests 9 5> are shown along with variations in the composition of the mixtures in Fig.3.49. 

Examining this in detail will show that the heat of reaction calculated in the above manner is indeed equal to the difference in the absolute enthalpies of the products and reactants. This will also show that the convention adopted that sets AHf of the elements equal to zero is valid in that the absolute enthalpies of the elements will mathematically cancel out of the equations. 

The size of this correction is relatively insignificant compared to either the quantity Qp or Q . In any case, the heat of reaction calculated from the bomb experiment is... 

If an incomplete reaction occurs, you should calculate the standard heat of reaction only for the products which are actually formed from the reactants that actually react. In other words, only the portion of the reactants that actually undergo some change and liberate or absorb some energy are to be considered in calculating the overall standard heat of the reaction. If some material passes through the reactor unchanged, it can contribute nothing to the standard heat of reaction calculations (however, when the reactants or products are at conditions other than 25°C and 1 atm, whether they react or not, you must include them in the enthalpy calculations as explained in Sec. 4.7-5). If several reactions occur simultaneously, your material balance must reflect what enters the reactor and is produced via the independent reactions. 

If the elemental reference state is used to calculate stream enthalpies, no heat of reaction calculation is necessary, and the same energy balance. Equation 13.4 or 13.51, applies. 

The CHETAH data bank contains data for about 500 group contributions and about 400 chemical compounds. The data stored for the current program is heavily oriented toward organic materials. Data for chemical compounds is stored for 1) common, frequently used molecules, 2) molecules which are too small to be estimated by second order groups, 3) common decomposition products, and 4) molecules which can be used as building blocks to create other molecules. The results for a typical heat of reaction calculation are shown in Table II. 

Our results in Table 6 were obtained with the NIST 133.84 kcal/mole [13], which is the smallest of those mentioned. If one of the others were used, this would simply make each of our AHf°(298 K) more positive by that increment per boron atom. However, any error in the boron heat of sublimation will not affect heats of reaction calculated with our AHf°(298 K) in Table 6 it will cancel, provided that solid boron is not part of the reaction. 

Table 1.2 Heats of Reaction Calculated for a Prototypical Process of Conversion of Pentagons to Hexagons at the Edge of a Graphene Layer"...

The total heat of reaction calculated from the sum of the isothermal and residual heats, q. + q, ranged from 60 to R5cal/g (resin) but showed no dependence on reaction temperature. However, the % residual heat decreased from 3 7 at B0°C to less... 

There are other methods that predict reactivity more reliably than the oxygen balance method. These methods, however, require the use of data generated by measurements. Stull devised a relatively simple Reaction Hazard Index or RHI that used both kinetic and thermodynamic data measurements. This index is a graphic model (nomagraph) that uses the Arrhenius activation energy and the decomposition temperature The latter term is the maximum adiabatic temperature reached by the products of a decomposition reaction. If data are available or can be measured, the RHI may be a very useful method to predict reactivity. Coffee described a method that predicts the explosive potential of a compound using thermal stability (measured), impact sensitivity (measured), and the heat of reaction (calculated). Compounds found to be thermally unstable and sensitive to impact were explosive. 

Measurements for seventeen reactions showed a generally smooth dependence of kn/ o upon the heat of reaction, calculated from the bond dissociation energies of reactants and products, and gave maximum effects for nearly thermoneutral reactions. Qualitatively similar trends have been reported by Lewis in the radical additions of thiols [79] and hydrogen bromide [80] to olefins. 

The bond length of the partial single bond Cl - C6 is predicted to be 0.06 A longer by the BLYP/6-31G method than by the RHF/6-31G method, whereas the other geometric parameters are found to be approximately equal by the two methods. The shown boat-like transition structure allows optimal interaction of the n -electrons at the carbon termini to form the new a-bond. The activation energy calculated at the BLYP/6-3IG level is in much better agreement with the experimental value of 121.3 kJ mol than the corresponding value from the RHF/6-31G calculation. It is also close to the value calculated at the MP2/6-31G level The heat of reaction calculated by... 

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