What are double decomposition reactions?
A double decomposition reaction is a reaction in which the positive ions and negative ions in two compounds switch partners to form two new compounds.
The equation is often written in the general form
The older term double decomposition has been largely replaced by the terms double displacement, double replacement, and metathesis.
Many double decomposition reactions are precipitation reactions.
Others are acid-base neutralization reactions.
Here is a good video on double replacement reactions.