# What must happen for a double replacement reaction to occur?

May 3, 2015

For a double replacement to occur, you must start with two ionic compounds in aqueous solution (dissolved in water). They must react to form an insoluble precipitate, an insoluble gas, or water.

The general reaction is in the form of AX + BY$\rightarrow$AY + BX. A and B are cations and X and Y are anions. In a double replacement, the ions switch partners.

Production of insoluble precipitate.

$\text{AgNO"_3("aq") + "NaCl(aq)}$$\rightarrow$"AgCl(s)" + "NaNO"_3("aq")

Production of an insoluble gas.

$\text{Na"_2"S(aq)" + "2HCl(aq)}$$\rightarrow$$\text{2NaCl(aq)" + "H"_2"S(g)}$

Production of water.

$\text{HNO"_3("aq)}$ + $\text{KOH(aq)}$$\rightarrow$$\text{KNO"_3("aq")}$ + $\text{H"_2"O(l)}$