Absolute ion hydration enthalpies and the role of volume within hydration thermodynamics

This paper reports that various thermodynamic properties in aqueous media for certain individual ions and for compounds are linear functions of the inverse cube root of the solid respective ionic and compound solid state volumes, V m –1/3 . This is similar to the situation which has been fully exploited in solid state thermodynamics and out of which Volume–Based Thermodynamics, VBT evolved. A short resume of these various VBT applications is provided for the general reader and an improved lattice potential energy equation emerges using the state of the art data presented in this paper

The thermodynamics of uranium salts and their hydrates - Estimating thermodynamic properties for nuclear and other actinoid materials using the Thermodynamic Difference Rule (TDR)

A comprehensive thermodynamic database of experimental standard enthalpy of formation, Δ f H o values, standard free energies of formation, Δ f G o and standard entropies, S o 298 for uranium salts and their hydrates at 298 K and 1 bar pressure is assembled. For many of these materials there exist experimental uncertainties or else multiple values (often considerably different) are listed for the same material. The aim of this paper is to showcase the ability of the Thermodynamic Difference Rule (TDR) to provide quite accurate estimates of such data (usually errors are less than 1%) and to provide guidance as to the most trusted value to adopt. In addition, where possible the TDR has been used to estimate missing literature values. New thermochemical data values are predicted and TDR is not reliant on possession of knowledge of crystal structures

Unique thermodynamic relationships for ΔfHo and ΔfGo for crystalline inorganic salts. I, Predicting the possible existence and synthesis of Na2SO2 and Na2SeO2

The concept that equates oxidation and pressure has been successfully utilized in explaining the structural changes observed in the M2S subnets of M2SOx (x = 3, 4) compounds (M = Na, K) when compared with the structures (room- and high-pressure phases) of their parent M2S 'alloy' [Martinez-Cruz et al. (1994), J. Solid State Chem. 110, 397-398; Vegas (2000), Crystallogr. Rev. 7, 189-286; Vegas et al. (2002), Solid State Sci. 4, 1077-1081]. These structural changes suggest that if M2SO2 would exist, its cation array might well have an anti-CaF2 structure. On the other hand, in an analysis of the existing thermodynamic data for M2S, M2SO3 and M2SO4 we have identified, and report, a series of unique linear relationships between the known Delta H-f(o) and Delta(f)G(o) values of the alkali metal (M) sulfide (x = 0) and their oxyanion salts M2SOx (x = 3 and 4), and the similarly between M2S2 disulfide (x = 0) and disulfur oxyanion salts M2S2Ox (x = 3, 4, 5, 6 and 7) and the number of O atoms in their anions x. These linear relationships appear to be unique to sulfur compounds and their inherent simplicity permits us to interpolate thermochemical data (Delta H-f(o)) for as yet unprepared compounds, M2SO (x = 1) and M2SO2 (x = 2). The excellent linearity indicates the reliability of the interpolated data. Making use of the volume-based thermodynamics, VBT [Jenkins et al. (1999), Inorg. Chem. 38, 3609-3620], the values of the absolute entropies were estimated and from them, the standard Delta S-f(o) values, and then the Delta(f)G(o) values of the salts. A tentative proposal is made for the synthesis of Na2SO2 which involves bubbling SO2 through a solution of sodium in liquid ammonia. For this attractive thermodynamic route, we estimate Delta G(o) to be approximately -500 kJ mol(-1). However, examination of the stability of Na2SO2 raises doubts and Na2SeO2 emerges as a more attractive target material. Its synthesis is likely to be easier and it is stable to disproportionation into Na2S and Na2SeO4. Like Na2SO2, this compound is predicted to have an anti-CaF2 Na2Se subnet

Complex phosphorus thermochemistry. Volume-based thermodynamics and the estimation of standard enthalpies of formation of gas phase ions: Delta H-f degrees(PCl4+, g) and Delta H-f degrees(PCl6-, g)

Energy-resolved collision-induced dissociation in a flowing afterglow-guided ion beam tandem mass spectrometer has recently enabled the accurate determination of the standard enthalpy of formation of the gaseous phosphorus pentachloride cation, Delta H-f degrees([PCl4+], g), found to be 414 +/- 17 kJ mol(-1) (giving a value of 378 +/- 18 kJ mol(-1) at 0 K). Such experimental values for the standard enthalpy of formation of gas phase complex are now being incorporated into the NIST standard reference data program. Such results, can, inter alia, provide a benchmark by which to test earlier computationally based methods which were made to estimate such quantities in the absence of any experimental data. The establishment of this value experimentally also affords us with the opportunity to explore the likely success of newer, simpler approaches. Previous large-scale direct minimization computations to estimate this (and other) standard enthalpies of formation match very well these new experimental results. This paper raises the question as to whether the much simpler volume-based thermodynamics (VBT) approach could yield equally satisfactory results and so circumvent, completely, the need for detailed modeling of the lattices involved. The conclusion is that the VBT approach portrays the extremely complex thermodynamics quite adequately. Thus for the purposes of obtaining basic thermodynamic data, complex modeling of the underlying structures involved may no longer be necessary. At least this should be the case for highly symmetrical ions, like PCl4+, where detailed packing with counterions is possibly less important than in other cases and where covalent interactions (less easily modeled) with neighboring ions is unlikely to be strongly featured. Other gaseous complex ion enthalpies of formation are also predicted here

Thermodynamic difference rules: a prescription for their application and usage to approximate thermodynamic data

Thermodynamic data are required for an understanding of the behavior of materials hut are often lacking (or even unreliable) for a variety of reasons such as synthetic problems, purity issues, failure to correctly identify hydrolysis products, instability of the material. etc. Thus, it is necessary to develop procedures for the estimation of that data. The Thermodynamic Difference Rules (TDR) are additive approximations by which the properties of materials are estimated by reference to those of related materials. These rules appear in the form of the reliable Hydrate Difference Rule (HDR), based on the well-established properties of the large number of known hydrates, and the somewhat less certain Solvate Difference Rule (SDR). These rules are briefly surveyed and their application carefully delineated by a scheme and demonstrated by a number of calculated examples

Single-ion entropies, S-ion degrees, of solids - a route to standard entropy estimation

Single-ion standard entropies, S-ion degrees, are additive values for estimation of the room-temperature (298 K) entropies of ionic solids. They may be used for inferring the entropies of ionic solids for which values are unavailable and for checking reported values, thus complementing the independent method of estimation from molar volumes (termed volume-based thermodynamics). Current single-anion entropies depend on the charge of the countercation, and so are difficult to apply to complex materials, such as minerals. The analysis of reported data here presented provides a self-consistent set of entropies for cations and charge-independent values for anions. Although the S-ion degrees values presented encompass only a limited set of ions, the retrieval of values for ions not listed is straightforward and is described. An unexpected and significant observation is that cation entropies are related to the molar volumes of the corresponding (neutral) condensed-phase metals

Volume-based thermodynamics : a prescription for its application and usage in approximation and prediction of thermodynamic data

Thermodynamics, as both thermochemistry and thermophysics, is fundamental and central to the science of matter and, in particular, of condensed materials. While extensive data resources for thermodynamic quantities do exist, none of the experimental, simulation, or theoretical studies can keep pace with the rate of synthesis of new materials or provide reliable data for hypothesized materials. Correlation methods can fill this gap. We describe a range of recently developed correlation methods that rely on volume to predict thermodynamic quantities. In parallel with these, thermodynamic difference rules, which describe how properties of materials (say, of a group of solvates) may be inferred from corresponding properties of materials that neighbor them in composition, have recently been reviewed