Heat of Formation at Infinite Dilution

What equations (8.30) and (8.31) reaUy tell us is that the total enthalpy can be determined if we Know the component heat of formation at infinite dilution and the temperature functionality of the activity coefficient for each constituent species 1. Let us now consider each of these in more detail. 

Every enthalpy calculation requires a basis. For purposes of this development, we will take, for aqueous species, the pure component heat of formation at 25°C and infinite dilution as the basis. Electrolyte solutions, as we have seen, contain either molecular or ionic species. Thus, in order to compute H (T) we will need formulations for both molecular and ionic species. 

For molecular species (e.g. CO2, NHs, H2S, H 2O, etc.) we normally can develop H by using component vapor-liquid equilibrium data in the following manner. The partial molar heat capacity at zero pressure has been correlated for many gases and the coefficients are given in the literature in terms of the Kobe equation (15)  

i = partial molar enthalpy of the vapor species i, cal/gm-mole Cp = partial molar heat capacity, cal/gm-mole C T° = basis temperature, 298.15 K 

Further, for vapor-liquid equilibrium we saw in Chapter III that 

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