Heat of reaction and enthalpy

Table 10.3 Enthalpy and heat of reaction as a function of temperature.

With as the reference temperature on which enthalpies and heats of reaction are based we have Enthalpy of entering feed ... 

Free energy is related to two other energy quantities, the enthalpy (the heat of reaction measured at constant pressure) and the entropy. S. an energy term most simply visualised as a measure of the disorder of the system, the relationship for a reaction taking place under standard conditions being... 

Note that the enthalpy includes sensible heat and heat of reaction effects as will be illustrated below. 

To solve the mass balance, it must be accompanied by the simultaneous solution of the energy balance (i.e., the solution of Equation (9.2.9)). To do this, Equation (9.2.9) can be written in more convenient forms. Consider that the enthalpy contains both sensible heat and heat of reaction effects. That is to say that Equation (9.2.10) can be written as ... 

We used HSC as the thermodynamic database [5]. Table 1 lists the enthalpy balance (heats of reaction, sensible heat, and latent heat for phase changes) for both the endothermic and the exothermic reactions defined above. 

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 Gibbs energy of formation of PbSe(cr) was measured in the temperature ranges 490 to 600 K and 650 to 858 K using electrochemical cells. The determined enthalpies and entropies of reaction at the mean temperatures of the temperature intervals are given in Table A-95. The quantities were recalculated to 298.15 K by the review and are tabulated in Table A-96. In addition, the corresponding values of the absolute entropy of PbSe(cr) at 298.15 K were calculated. All calculations employed the selected heat capacity of PbSe(cr), the selected thermodynamic properties of selenium, and the data for Pb(cr, I) in [89COX/WAG]. 

Skill 5.1a-Perform calculations using specific heat, heats of fusion, heats of vaporization, and heat of reaction (enthalpy)... 

Table 18.2 Enthalpy of activation and heat of reaction of the Bergman reaction.

Table A-26 Enthalpy, entropy and heat capacity of reaction for the hydrolysis reactions of Th(IV) in 1 m (Na)C104. In the last two colunuis are given the enthalpy and entropy of reaction divided by the number of OH-groups in the complex.

Atomization Energies, Heats of Formation, and Heats of Reaction. Gas-phase enthalpies of formation are readily calculated from atomization energies (Section 15.14), and gas-phase heats of reaction are readily found from gas-phase heats of formation of reactants and products. All three of these related quantities are considered in this subsection. Throughout this section, only gas-phase reactions are considered because this avoids the substantial contributions of intermolecular interactions in liquids and solids. To convert a calculated gas-phase reaction energy to one involving condensed phases, we use the experimental energies of condensation of substances. 

Because His a state function, the value of AH is independent of the details of the reaction. It depends only on the initial state (the reactants) and the final state (the products). The key relation in this chapter is that between enthalpy change and heat of reaction ... 

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