Specific heat capacity enthalpy method

The fourth and final chapter in this voliune is given over to the determination, both experimentally and by computation, of the values of the parameters associated with chemical reactions. Thermochemistry for enthalpy, the determination of the entropies, specific heat capacities and Gibbs energy values ultimately lead to the determination of the equilibrium constants. Analysis of the different thermodynamic tables and methods for estimating unknown values enable us to proceed to the practical application and finally computation of the equilibria by the equilibrium constant method and minimization of Gibbs energy. 

In order to use the methods presented above to classify the chemical elements, the problem we are first faced with is to decide the characteristics this classification is built upon. We started with 10 physical properties relative atomic mass, A (1), density, p (2), melting point, Tf (3), boiling point, T, (4), Pauling electronegativity, x (5), enthalpy of vaporization, AH (6) and fusion, AHf (7), specific heat capacity, Cs (8), first ionization energy, E (9), and covalent radius, r (10). 

The a.c. calorimetric technique is very well suited to measure pretransitional specific heat capacities. Indeed it measures Cp directly and not the enthalpy H. This method has been extensively used for the investigation of liquid crystals by Johnson [22], Huang [23-25], Garland [4,26,27] and their coworkers. 

They include physical methods such as the determination of electrical resistivity, enthalpy or specific heat capacity of the semi-crystalline polymer which require knowledge of the values of these different parameters for both the crystalline and amorphous phases. Spectroscopic methods such as n.m.r. and infrared spectroscopy which have been outlined in Section 3.6 have also been employed. In general there is found to be an approximate correlation between the different methods of measurement employed although the results often differ in detail. 

The equilibrium state is generated by minimizing the Gibbs free energy of the system at a given temperature and pressure. In [57], the method is described as the modified equilibrium constant approach. The reaction products are obtained from a data base that contains information on the enthalpy of formation, the heat capacity, the specific enthalpy, the specific entropy, and the specific volume of substances. The desired gaseous equation of state can be chosen. The conditions of the decomposition reaction are chosen by defining the value of a pair of variables (e.g., p and T, V and T). The requirements for input are ... 

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