The Thermodynamic Sinks of this World » American Scientist

June 26, 2013

Thermodynamic sinks: oxides, alkaline cation + molecular anion, fluorides, dissolved salts #chemistry
by Nobel Laureate Roald Hoffmann

Let’s use some simple chemistry to get a feeling for the thermodynamic sinks of this world. …. Here is the first principle of stability, one we have already seen in the reaction forming water: Form oxides. ….The prescription is obvious: Form oxides, form solid state, ionic compounds. The elements don’t stand a chance, except for the early noble gases …. one finds that all carbonates are very stable, as are most salts containing nitrate (NO3-), sulfate (SO42-), phosphate (PO43-) and silicate ions…..
There is a pattern emerging in the nature of the more stable compounds: It’s not simply ionic bonding (Na+Cl-, Li+H-), but ionic bonding between an alkali or alkaline earth cation and a molecular anion (CO32-, SiO44-). Of course, within each molecular ion there lurks ionicity… Ions within ions!
But there are compounds more stable than oxides, and these are fluorides—for example, CaF2, fluorite, or Na3AlF3, cryolite. In these even more ionicity is provided than in oxides. ….
Also, in the temperature range where water is a liquid, a good number of salts, hardly all, dissolve in water with a negative Gibbs energy of solution….
So my tentative answer to the question posed at the beginning is not romantic. The final product (at P = 1 atmosphere and 298 kelvin) will be a messy soup of cations of the less electronegative elements (including the transition metals) with molecular anions, in water. “

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