Double Replacement Reactions
Ions swap partners, often forming a precipitate, gas or water.
About this topic
In a double replacement (or double displacement) reaction, two compounds exchange ions: AB + CD → AD + CB. These reactions usually occur in aqueous solution and proceed when one product is a precipitate, a gas or a molecular compound such as water.
Three driving forces predict whether a reaction happens. A precipitate forms if the new combination is insoluble, such as barium chloride and sodium sulfate giving solid barium sulfate. A gas forms in cases like sodium carbonate plus hydrochloric acid, which produces carbon dioxide via unstable carbonic acid. Water forms in acid-base neutralisation, such as HCl + NaOH giving NaCl + H2O. If none of these occurs, all ions just remain in solution and there is no net reaction.
Example: mixing lead(II) nitrate and potassium iodide gives a bright yellow precipitate, Pb(NO3)2 + 2KI gives PbI2 + 2KNO3. Antacid tablets neutralise stomach acid this way, and water softening removes calcium ions as insoluble carbonate.
Students often forget to swap the ions correctly and to rebalance charges in the new formulas, writing, say, NaCl2. Work out the formulas from ion charges. Also remember that no oxidation numbers change in these reactions, which separates them from redox reactions.
Key ideas
- AB + CD → AD + CB
- Driving force removes ions
- Neutralization is one type
Quick check
Use cases: where Double Replacement Reactions helps
- Homework: review the key idea behind Double Replacement Reactions before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Double Replacement Reactions without notes.
- Visual learning: play with the interactive lab to see how Double Replacement Reactions changes when you adjust its inputs.
- Teaching a friend: explain Double Replacement Reactions in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Double Replacement Reactions?
Ions swap partners, often forming a precipitate, gas or water.
What will I learn in Double Replacement Reactions?
AB + CD → AD + CB. Driving force removes ions. Neutralization is one type.
Is Double Replacement Reactions part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Double Replacement Reactions lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Double Replacement Reactions?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.