Question

when is a chemical equation cosidered a double dis placement reaction

Answer 1

When the two reactants react with each other and exchange there ions and forms two new products are double displacement reaction

Answer 2

Double Displacement reaction is a reaction in which the ions in the reactants are exchanged to form a precipitate.
For example ..
AgNO3 + NaCl ---> AgCl + NaNO3

Hope it helps you