ABSTRACT
In contrast to the many sulfates (see Chapter 4), there are very few anhydrous sulfites about which much is known. (See Figure 3.1.) They are usually prepared by the dehydration of hydrates and thus may not be entirely water-free. This may affect the decomposition reactions, since in some instances water and SO
evolve simultaneously. High temperature thermodynamic data are available only for three sulfites: calcium, potassium,
and sodium. Most sulfites are fairly unstable, decomposing at relatively low temperatures. The decomposition reactions are not always exactly known, with diverse decomposition products, including sulfur, being reported. There are two major decomposition reactions: (1) decomposition to the oxide and SO
, and (2) oxidation-reduction (disproportionation) to the sulfate and oxide and SO
, i.e.,
2 MSO
= MSO
+ MO + SO
This reaction generally occurs at higher temperatures. Details of these two reactions are discussed under the individual elements.
