The reactants need not to be dissolved for metathesis reactions to take place. An example of this is the formation of barium thiocyanate when boiling a mixture of and in water:
However, when two aqueous solutions are mixed the anions and cations come together and form a precipitate, or gas. There are 3 types of metathesis reactions: precipitation reactions, neutralization reactions, and gas formation reactions.
Reactions In Aqueous Solution: Metathesis ..
It allows us to see what caused the solids, liquids, or gases to form.
A metathesis reaction is when cations and anions switch partners (double replacement reaction).