Functional groups, contributions thermodynamic properties

These results show the useful application of group contribution thermodynamic models to predict phase equilibria properties, and the necessity of a rational partition of a molecule into appropriate functional groups that take into account the basis of its chemical bonding. 

Table A4.1 summarizes the equations needed to calculate the contributions to the thermodynamic functions of an ideal gas arising from the various degrees of freedom, including translation, rotation, and vibration (see Section 10.7). For most monatomic gases, only the translational contribution is used. For molecules, the contributions from rotations and vibrations must be included. If unpaired electrons are present in either the atomic or molecular species, so that degenerate electronic energy levels occur, electronic contributions may also be significant see Example 10.2. In molecules where internal rotation is present, such as those containing a methyl group, the internal rotation contribution replaces a vibrational contribution. The internal rotation contributions to the thermodynamic properties are summarized in Table A4.6.

In general, procedures for estimating physical and thermodynamic properties and functions can be divided into two categories, namely, group contribution methods and semi-empirical correlations. It is usually difficult, if not impossible, to employ a semi-empirical correlation for predicting the properties of a new material or those of an existing material at a condition different from that under which the available data were obtained. In contrast, the group contribution method, which is based on the assumption that the property of a material is contributed from... 

A group contribution method, specifically, the second-order law, Is adopted In this work for estimating the physical and thermodynamic properties and functions of organic chemicals. 

Group contribution methods, such as the one discussed above, have been reasonably successful for estimating many physical and thermodynamic properties of pure substances and mixtures, especially when each molecule contains no more than one nonalkyl functional group. These methods dissect a molecule into functional groups that are assumed to be independent of each other. Tliat is, a functional group is assumed to behave the same in its interactions with other functional groups independent of the molecule of which it is... 

Vibrational spectroscopy has been used to make significant contributions in many areas of chemistry and physics as well as in other areas of science. However, the main applications can be characterized as the study of intramolecular forces acting between the atoms of a molecule the intermolecular forces or degree of association in condensed phases the determination of molecular symmetries molecular dynamics die identification of functional groups, or compound identification the nature of the chemical bond and the calculation of thermodynamic properties. Ciuient plans are for the reviews to vary, from the application of vibrational spectroscopy to a specific set of compounds, to more general topics, such as force-constant calculations. It is hoped tiiat many of the articles will be sufficiently general to be of interest to other scientists as well as to the vibrational spectroscopist. 

The elucidation of a substitution reaction mechanism depends on reliable kinetic and thermodynamic data obtained by measuring changes in the reaction rate as a function of a chemical property (e.g., concentration, pH, ionic strength, solvent polarity) or physical quantity (e.g., temperature). The determination of an empirical rate law, the observation of steric or electronic effects induced by the entering, spectator, or leaving groups, and the estimation of activation parameters from variable-temperature experiments (i.e.. A// and Aj ) contribute to the adjudication of a plausible mechanism for a given reaction. 

The UNIFAC model defines functional groups, which make up the stractures of compounds. Each frmctional group makes a rrrtique contribution to the compound property. The interaction parameters obtained for a small number of groups using thermodynamically consistent data can be used for mrrlti-component systems. 

Nitta et. al. ( 7) extended the group interaction model to thermodynamic properties of pure polar and non-polar liquids and their solutions, including energy of vaporization, pvT relations, excess properties and activity coefficients. The model is based on the cell theory with a cell partition function derived from the Carnahan-Starling equation of state for hard spheres. The lattice energy is made up of group interaction contributions. 

Studies in the last decade show that iron sulfide minerals are very reactive in the reductive transformation of chlorinated aliphatic pollutants. These minerals, present in sulfate-reducing anaerobic environments, likely contribute to in-sUu transformation of chlorinated aliphatic pollutants and have potential application in remediation technologies. Solution pH, the presence of organic co-solutes with functional groups representative of natural organic matter, and the thermodynamic or molecular properties of the halogenated aliphatic pollutant all influence the rates and/or products of pollutant transformation. 

The group contribution techniques are based on the assumption that the contributions of different functional groups to the thermodynamic property are additive. The energy of vaporization of a solvent or polymer is... 

Roberts ( 1 1) surveyed the superconductive properties of the elements and recommended a critical temperature of 1.175 0.002 K for Al(cr). Since this temperature is so low, the effects of superconductivity on the thermodynamic functions are not considered. The entropy contribution due to superconductivity will be less than 0.002 J X mol . The data of Giauque and Meads (j ) and Downie and Martin (3) agree at temperatures up to 150 K but drift apart by 0.2 J X mol at 200 X and 0.17 J X mol at 300 K, with the Downie and Martin study being lower. The Takahashi (4, 5) study is even lower at 298 X. The high temperature heat capacity values are derived from the enthalpy study of Ditmars et al. (9). Their curve is intermediate between those derived from previous studies (4, 5, 6, 7, 8) and implies a flatter Cp curve near the melting point (in comparison to previous interpretations). Numerous other heat capacity and enthalpy studies are available but were omitted in this analysis. A detailed discussion of the Group IIIA metals (B, Al, and Ga) is in preparation by the JANAF staff. 

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