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HOME > PAST ISSUE > July-August 2013 > Article Detail

MARGINALIA

The Thermodynamic Sinks of this World

What would an elemental soup cook up to?

Roald Hoffmann

Nothing Is Simple

Going back to the cartoon world of H2, Cl2, O2 and Na, you would get mostly NaCl (s) and H2O (l) at equilibrium at 298 kelvin. Not really—for mixing is most certainly allowed, and salt dissolves spontaneously in water, as you well know. And perhaps I should worry about other reactions among the six species. For instance Na with H2 (to give NaH [s]), Na with O2 (to give Na2O [s]), Cl2 with H2 (to give HCl [g]), Cl2 with O2 (to give Cl2O or ClO2, both known). And I haven’t started to be concerned about ternaries (compounds of three elements with each other); I’ve kept my world simple with binaries, isolated from each other. Remember that other pyrotechnic lecture demonstration—dropping a chunk of sodium into water?

Na (s) + H2O (l) ↔ NaOH (aq) + ½ H2 (g) ΔH = –183 kJ/mol

I write NaOH (aq), the “aq” standing for aqueous, because NaOH is very soluble in water (ΔG for solution is –42 kJ/mol). Now how about quaternaries?








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