Which equation represents a double replacement reaction?

Which equation represents a double replacement reaction?

• A. C + H + O --> H2O + CO2
• B. AB + CD --> AD + CB
• C. A + B --> AB
• D. AB --> A + B

Answer: (B)

Double replacement reactions involve two ionic compounds that swap their partners to form two new compounds. In the pattern AB + CD → AD + CB, the cation from the first compound pairs with the anion from the second, and the cation from the second pairs with the anion from the first, giving AD and CB. That exchange of partners is the defining feature. This equation exactly shows that swap, so it represents a double replacement reaction. The other types shown do not involve exchanging partners: shifting elements to form water and carbon dioxide is a combustion/oxidation process; AB → A + B is a decomposition; and A + B → AB is a synthesis.

Double replacement reactions involve two ionic compounds that swap their partners to form two new compounds. In the pattern AB + CD → AD + CB, the cation from the first compound pairs with the anion from the second, and the cation from the second pairs with the anion from the first, giving AD and CB. That exchange of partners is the defining feature.

This equation exactly shows that swap, so it represents a double replacement reaction. The other types shown do not involve exchanging partners: shifting elements to form water and carbon dioxide is a combustion/oxidation process; AB → A + B is a decomposition; and A + B → AB is a synthesis.