Standard molar entropy

About: Standard molar entropy is a research topic. Over the lifetime, 1586 publications have been published within this topic receiving 29886 citations.

Bonding properties and vibrational entropy of transition metal MeB2 (AlB2) diborides

Abstract: The transition metal diborides MeB2 were chosen as an example to illustrate an approach introduced by us, by which existing thermodynamic information can be systematized and new information generated. We consider trends in the melting temperature, the enthalpy of formation and lattice vibration properties as the metal Me varies along the 3d, 4d and 5d transition metal series. The trends show a consistent picture which can be explained from the electronic density of states by a rigid-band like argument. This fact gives us confidence to apply the regularities and obtain new information by interpolation and extrapolation procedures. In particular, we estimate the standard entropy S⊖ at 298.15 K for stable AlB2 structure compounds where there are no previous measurements and for some metastable compounds (Me ≡ Sc, V, Cr, Mn, Y, Mo, Tc, WandRe). The results are compared with estimates based on various empirical methods. In the Me-B systems, the MeB2 phase may be stable at all temperatures, or be a high-temperature phase or a metastable phase. We explain the observed trend. Through the use of thermodynamic phase diagram calculations (the so-called CALPHAD method), we study the thermodynamic properties of the metastable AlB2 structure phase FeB2.

Structural effects on the binding of amine drugs with the diphenylmethyl functionality to cyclodextrins. I. A microcalorimetric study.

Abstract: Solution calorimetry has been employed to evaluate the stability constants and enthalpy changes associated with complex formation between α-, β, or -γ-cyclodextrin (CD) and a group of amine compounds having the diphenylmethyl functionality. Data from thermal titrations of the compounds were analyzed using nonlinear least squares. The standard free energy decrease accompanying the formation of inclusion complexes is generally due to a negative standard enthalpy change (ΔH°). The standard entropy change (ΔS°) was negative, except in the case of complexes formed with γ-CD. Of the 13 compounds studied, only 2 formed complexes with 1:2 (compound: (β-CD) stoichiometry, terfenadine · HC1 and cinnarizine · 2HC1. All the others formed 1:1 complexes. The structural effect on the stability constants, thermodynamics, and inclusion geometry was explored by relating the calorimetric results to the chemical structures of the guest molecules and the cavity sizes of the CD molecules. The results suggest that one of the phenyl groups of the diphenylmethyl functionality resides in the CD cavity and is in van der Waals contact with the inside wall of the CD cavity. In the case of α- and β-CDs, van der Waals interaction dominates in the stabilization. On the other hand, the interaction between these compounds and γ-CD is largely entropically driven. Adiphenine · HC1 forms a more stable complex with β-CD than proadifen · HC1, suggesting that hydrogen bonding to the carbonyl oxygen by the hydroxyl group on the rim of the CD ring can influence the strength of the binding interaction.