To spot a double replacement reaction, look for certain signs in the starting materials and the products. In this type of reaction, two compounds swap parts, often involving ionic compounds in water.

Key Signs to Look For:

1. Starting Materials (Reactants):

   • Usually, there are two ionic compounds. For example, you might see $AB + CD$. Here, $A$ and $C$ are positive ions (called cations), and $B$ and $D$ are negative ions (called anions).

2. End Products:

   • The result will also be two new ionic compounds: $AD + CB$. This means that the positive ion from one compound pairs with the negative ion from the other compound and vice versa.

What to Watch For:

• Keep an eye out for signs like a solid forming, a gas being released, or water being produced in the results.

  • Solid Formation: When you mix silver nitrate ($AgNO_3$) and sodium chloride ($NaCl$), you create silver chloride ($AgCl$), which is a solid:

    $AgNO_3(aq) + NaCl(aq) \rightarrow AgCl(s) + NaNO_3(aq)$

  • Gas Release: For example, when an acid like hydrochloric acid meets a carbonate like sodium bicarbonate, it produces carbon dioxide:

    $HCl(aq) + NaHCO_3(s) \rightarrow CO_2(g) + NaCl(aq) + H_2O(l)$

By knowing these signs, you can easily find double replacement reactions!