Thermochemistry of fluorine compounds. Part I. Reaction calorimetry in fluorosulphuric acid
Some applications of fluorosulphuric acid as a calorimetric medium are outlined. The heats of formation of potassium, sodium, cupric, nitrosonium, and nitronium fluorosulphates were measured in it, and of nitrosonium hydrogen sulphate and disulphate in alkaline hypochlorite solutions. The regularities in heats of formation between perchlorates, hydrogen sulphates, and fluorosulphates of the same cations are correlated by heat cycles. The proximity of values for the latter pairs follows from the isoelectronic structure of their ions. Heats of protonation of water and organic bases in fluorosulphuric acid are approximately related to ionisation in the solvent. Values for the enthalpies and free energies of other ionic fluorosulphates can be estimated from heat cycles or by comparison with hydrogen sulphates. The stability of unknown fluorosulphates are predicted.