Application of thermodynamic data

Many of the text-books e.g. ref. 250) and sources of data e.g. ref. 291) listed in earlier sections describe the applications of thermodynamic data, but there are a number of books concerned mainly with physicochemical calculations which also provide examples of the derivation of scientifically and technologically important data by means of thermodynamics. Thus Smith s book Chemical Thermodynamics, A Problems Approach , which is of degree level, relates theory to worked examples, and Guggenheim and Prue s Physicochemical Calculations is of this type. ... 

Isothermal titration calorimetry (ITC) has gained much attention recently, as the application of thermodynamic data in the lead generation process has been proposed as a strategy both to improve the quality of lead series and to allow for a more effective lead optimization process [30-32]. The technique enables the determination of the affinity, the binding enthalpy, and the stoichiometry in a single experiment within a time frame of <1 h using as littie as 100 pg of a target protein. 

For pure organic materials, it is also possible to calculate the heating value starting from the heats of formation found in tables of thermodynamic data. The NHV is obtained using the general relation of thermochemistry applicable to standard conditions of pressure and temperature (1 bar and 25°C)) f 9j... 

The term heat of adsorption has been defined in a number of different ways. Unfortunately, the initial and final states of the adsorption system and the conditions under which the exchange of heat takes place have not always been adequately defined. As in all applications of thermodynamics, it is essential that the experimental data refer to a system which has reached equilibrium. 

Vapor/liquid equilibrium (XT E) relationships (as well as other interphase equihbrium relationships) are needed in the solution of many engineering problems. The required data can be found by experiment, but such measurements are seldom easy, even for binaiy systems, and they become rapidly more difficult as the number of constituent species increases. This is the incentive for application of thermodynamics to the calculation of phase-equilibrium relationships. 

One practical problem of the determinant method is the common unavailability of thermodynamic data and phase diagrams for multiphase compounds. For practical applications, an estimate obtained from data for binary compounds of the multinary system may be useful. 

The fact that we are gathered together at a conference on "Thermodynamics on Aqueous Systems with Industrial Application" indicates the importance of thermodynamic data on aqueous solutions. In particular, there is a great need for data on high temperature aqueous systems. Because of the experimental difficulties, there are relatively few measurements on these systems and yet they are of very great industrial importance. 

Sources of thermodynamic data which the authors have found to be valuable in hydrometallurgical applications have been assembled in Table II. 

Tin K and P in kbar) however, its application to other thermobaric conditions is not so appropriate. The most satisfactory formulations for the exchange reaction 5.216 are those of Slavinskiy (1976), Ganguly (1979), Saxena (1979), and Dahl (1980), which are based on a large body of thermodynamic data, petrologic studies, and natural observations. 

EM plays a crucial role in the development of thermodynamic data, especially for defective solids, multi-phase solids and solids with coexisting intergrowth structures. These microstructural details, which are essential to catalytic properties, cannot be revealed readily by other diffraction methods which tend to average structural information. The formation of anion vacancies in catalytic reactions and the resulting extended defects are described here, from which an improved understanding of the formation of CS planes and their role in catalysis can be obtained. These general results are applicable to other CS structures. 

Chapters 15 and 16 especially demonstrate the broad range of application of thermodynamics to chemical processes. In the discussions of the Haber cycle, synthesis of diamond, solubility of calcite, and the thermodynamics of metabolism, techniques are used to solve a specific problem for a particular substance. On the other hand, in the discussion of macrocyclic complexes, the description and interpretation involves the comparison of the properties of a number of complexes. This global approach is particularly helpful in the description of the energetics of ternary oxides in Chapter 15 and the stabilities of proteins and DNA in Chapter 16, where useful conclusions are obtained only after the comparison of a large amount of experimental data. 

The three appendices in this volume give selected sets of thermodynamic data (Appendix 5), review the statistical calculations covered in Principles and Applications (Appendix 6), and summarize the equations and parameters required to calculate the properties of electrolyte solutions, principally from Pitzer s equations (Appendix 7). 

Kelley, K. K., Contributions to the Data on Theoretical Metallurgy IV. Metal Carbonates — Correlations and Applications of Thermodynamic Properties, U.S. Bur. Mines Bull. 384. 1935 Bull. 601, 1962. 

In addition to the analytical applications discussed above, controlled-potential methods are used for the evaluation of thermodynamic data and diffusion coefficients in both aqueous and nonaqueous solvents. Polarographic and voltammetric methods provide a convenient and straightforward means for evaluation of the diffusion coefficients in a variety of media. The requirements are that the current be diffusion-controlled, the number of electrons in the electrode reaction be known, and the concentration of the electroactive species and the area of electrodes be known. With these conditions satisfied, diffusion coefficients can be evaluated rapidly over a range of temperatures and solution conditions. 

Perhaps a more fundamental application of crystal field spectral measurements, and the one that heralded the re-discovery of crystal field theory by Orgel in 1952, is the evaluation of thermodynamic data for transition metal ions in minerals. Energy separations between the 3d orbital energy levels may be deduced from the positions of crystal field bands in an optical spectrum, malting it potentially possible to estimate relative crystal field stabilization energies (CFSE s) of the cations in each coordination site of a mineral structure. These data, once obtained, form the basis for discussions of thermodynamic properties of minerals and interpretations of transition metal geochemistry described in later chapters. 

An attempt to make this application prompted the appearance of The Thermodynamics of Soil Solutions (Oxford University Press, 1981). Besides its evident purpose, to demonstrate the use of chemical thermodynamics, this book carried a leitmotif on the fundamental limitations of chemical thermodynamics for describing natural soils. These limitations referred especially to the influence of kinetics on stability, to the accuracy of thermodynamic data, and to the impossibility of deducing molecular mechanisms. The problem of mechanisms vis-a-vis thermodynamics cannot be expressed better than in the words of M. L. McGlashan 2 what can we learn from thermodynamic equations about the microscopic or molecular explanation of macroscopic changes Nothing whatever. What is a thermodynamic theory (The phrase is used in the titles of many papers published in reputable chemical journals.) There is no such thing. What then is the use of thermodynamic equations to the chemist They are indeed useful, but only by virtue of their use for the calculation of some desired quantity which has not been measured, or which is difficult to measure, from others which have been measured, or which are easier to measure. This point cannot be stated often enough. 

The main problem in the application of thermodynamic models to the computer treatment of experimental results is that most experimental data are obtained for simple systems (active carbons prepared in conditions close equilibrium), because just such systems are readily available for laboratory studies. 

The simplest models are applicable to the treatment of existing experimental data, while for industrial needs the imitation of nonsteady-state or/and random fluxes is desirable. The author recommends the analysis of the applicability of thermodynamic models of microporous material formation to complexes of experimental data (adsorption-desorption, adhesion, mechanical stability and percolation characteristics). 

The compressibility factor is by definition Z = PV/RT values of Z and of (dZ/BT)P are calculated directly from experimental PVT data, and the two integrals in Eqs. (6.40) through (6.42) are evaluated by numerical or graphical methods. Alternatively, the two integrals are evaluated analytically when Z is expressed by an equation of state. Thus, given PVT data or an appropriate equation of state, we can evaluate HR and SR and hence all other residual properties. It is this direct connection with experiment that makes residual properties essential to the practical application of thermodynamics. 

These equations are restatements of Eqs. (6.37) and (6.38) wherein the restriction of the derivatives to constant composition is shown explicitly. They lead to Eqs. (6.40), (6.41), (6.42), and (11.20), which allow calculation of residual properties and fugacity coefficients from PVT data and equations of state. It is through the residual properties that this kind of experimental information enters into the practical application of thermodynamics. 

Table 21 shows a variety of thermodynamic data collections and the elements considered. The thermodynamic data are usually not available in a current database format (exception CHEMVAL 6 as dBASE file) but in a form which is needed for the specific program. To use thermodynamic data in PHREEQC which are applicable e g. for EQ 3/6 or PHREEQC, they have to be converted into the respective format (e g. PHREEQC) using a transfer program. 

---