Calculation of the Reaction Enthalpy

The condensation energy transfer to the reactant was taken into account in the calculation of the reaction enthalpy (r = 0.5 for CaCOs and 0.6 for two other reactants)... 

Calculation of the reaction enthalpies for the formation of the compounds shown in Figure 7.7 gave negative values whereas for the Lewis-Acid 6(0 1-15)3 mol positive (DFT ... 

Section 6.11, when we calculated the enthalpy change for an overall physical process as the sum of the enthalpy changes for a series of two individual steps. The same rule applied to chemical reactions is known as Hess s law the overall reaction enthalpy is the sum of the reaction enthalpies of the steps into which the reaction can be divided. Hess s law applies even if the intermediate reactions or the overall reaction cannot actually be carried out. Provided that the equation for each step balances and the individual equations add up to the equation for the reaction of interest, a reaction enthalpy can be calculated from any convenient sequence of reactions (Fig. 6.30). 

Table 4 shows that the calculated graduation of the reaction enthalpies agrees well with that of the experimental values as well as the free reaction enthalpies. 

The solvent influence, calculated with the Huron-Claverie method, reverses the qualitative graduation of the reaction enthalpies of the propagation steps as the chain length increases, in comparison to the gas phase. The same results were obtained using the same model system by Basilevski et al.125), while using a fundamentally different model for the solvent influence. 

According to these parameters, the activation energy of the peroxyl radical reaction with aromatic amine can be calculated using the reaction enthalpy by the equation [54]... 

Besides the second law method, there is another way of extracting reaction enthalpies from gas-phase equilibrium constants. This alternative involves the determination of a single value of an equilibrium constant at a given temperature and the calculation of the reaction entropy at the same temperature. From equations 2.54 and 2.55, we obtain... 

It is generally agreed that the third law method yields more accurate values than the second law method because it does not require any assumption regarding the temperature variation of the reaction enthalpy and entropy. The usual procedure to obtain third law data is to calculate the reaction enthalpy and entropy for each experimental value of Kp and take the average of all the values derived for a given temperature. 

The calculation of the molar enthalpy of reaction 10.17, Ar//(10.17), requires the amount of substance of /ran,y-azobcnzcnc consumed. In seven independent experiments, n was determined spectroscopically and varied between 4 x 10-7 mol and 15 x 10-7 mol [191], Note that it was not possible to use equation 10.13, even if the quantum yield were known, because the the radiant energy (E) supplied to the photochemical reactor was not measured. 

One real value of tables of standard enthalpies of formation is that they permit the calculation of the standard enthalpy of any reaction for which all the reactants and products are listed it is not necessary to do an experimental measurement. Based on Hess s law, the basic premise of the use of tables is that the enthalpy of reaction is the difference between the sum of the enthalpies of the formation of the products and the sum of the enthalpies of formation of the reactants. That is,... 

In Equation 7.24, the adiabatic temperature rise is calculated for the final reaction mass. This criterion calculates the active temperature difference for an efficient cooling as a function of the reaction enthalpy. 

Calculation of the Adsorption Enthalpy of n-Paraffins in Nanoporous Crystalline and Ordered Acid Catalysts, and Its Relation with the Activation Energy of the Monomolecular Catalytic Cracking Reaction... 

CALCULATION OF THE FREE ENTHALPY OF REACTION FROM GROUP CONTRIBUTIONS... 

Calculation of the free enthalpy of reaction from group contributions, 752 Calorimetric properties, 109 Capacity... 

Corrosion of refractories and ceramics involves consideration of (i) acid-base effects involved in the corrosion of refractory (ii) verification of the thermal stability of each constituent (iii) calculation of the free enthalpy of all possible reactions that might occur in the corrosion of the refractory or ceramic compound. Kinetic data are also useful in understanding the corrosion and selection of the refractory compound for a specific application. 

The functions G(a) and K(a) are dependent and determined by a separate droplet dissolution model. Once calculated they are part of the 3EM where they prescribe the mass fractions in the E.E.s and in the L.E. as well as the enthalpy that is relevant to the calculation of the reaction temperature. 

The RSE is calculated here as the difference between the homolytic C-C bond dissociation energy in ethane (5) and a symmetric hydrocarbon 6 resulting from dimerization of the substituted radical 2. By definition the C-C bonds cleaved in this process are unpolarized and, baring some strongly repulsive steric effects in symmetric dimer 6, the complications in the interpretation of substituent effects are thus avoided. Since two substituted radicals are formed in the process, the reaction enthalpy for the process shown in Equation 5.5 contains the substituent effect on radical stability twice. The actual RSE value is therefore only half of the reaction enthalpy for reaction 5.5 as expressed in Equation 5.6. 

The Knudsen effusion mass spectrometric method will be briefly described and Illustrated. The influence of various assumptions about the geometry and electronic structure of the molecules on the third law values of the reaction enthalpies obtained will be discussed. The development and use of empirical models for calculating dissociation and atomization energies will be Illustrated and their value as a bridge between experimental values and semi-empirical and theoretical calculations demonstrated. 

For the third law evaluations of the reaction enthalpies from mass spectrometric equilibrium measurements the Gibbs free energy functions of the reactants are needed. Likewise the enthalpy functions are needed in order to correct the second law reaction enthalpies obtained at the average temperature of measurement to the desired reference temperature. These thermal functions can be calculated according to standard statistical... 

The first step was confirmed to be exothermic (AH —7.5 kj moH ) which makes a reversible rehydrogenation under reasonable physical conditions almost impossible. The reaction enthalpy for the second step was determined to be about 32 kJ mol H2. The experimental data have been confirmed by first-principles DFT calculations of the dehydrogenation enthalpies, showing that the first step of dehydrogenation is indeed exothermic [187, 188]. 

The third-law method is based on a knowledge of the absolute entropy of the reactants and products. It allows the calculation of a reaction enthalpy from each data point when the change in the Gibbs energy function for the reaction is known. The Gibbs energy function used here is defined as... 

Table A-26 Calculation of the standard enthalpy change of the reaction Na2Se03(cr) Pb PbSe03(cr) + 2Na. The sources of the data are indicated.

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