Heat capacity of formation

Af Cp(i) is the standard heat capacity of formation of species i at constant pressure and C°m(i) is the standard molar heat capacity of species i at constant pressure. Equation 3.2-12 can be written in the form... 

The equation for the standard molar heat capacity of formation of an isomer group can be obtained by using... 

Equation (3.5-18) has been written in terms of molar heat capacities Cpm(i), rather than heat capacities of formation, because the heat capacities of the elements are on both sides and cancel. The second term of this equation is always positive because the weighted average of the squares is always greater than the square of the average. Equation 3.5-18 is in accord with LeChatelier s principle As the temperature is raised, the equilibrium shifts in the direction that causes the absorption of heat. Equation 3.5-18 can also be derived using CP = — T(d2G/dT2)P (equation 2.5-25). 

AfCp(y) standard heat capacity of formation of species j (J K 1 mob1)... 

Similarly, ACp, the heat capacity of formation , might be tabulated instead of Cj, but the reason for this is different. The amount of heat capacity data for metallurgical substances is still rather restricted and, since the data are mostly obtained by drop calorimetry (see below), often not very reliable. Since it is much easier to estimate changes in, rather than actual, heat capacities, the former might be tabulated. 

TABLE 6.1 Enthalpies and Gibbs Energies of Formation, Entropies, and Heat Capacities of Organic Compounds... 

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