Chapter 7 · Chemical Reactions
7.10Classifying Chemical Reactions
10 min · two checks
Predict
A + B → AB and AB → A + B are which pattern?
The idea
- Classify reactions as combination, decomposition, single replacement, or double replacement.
- Say which of those patterns are typically redox.
One useful sort looks at how atoms regroup. Combination: two substances become one. Decomposition: one becomes two or more. Single replacement: an element swaps into a compound and frees another element, which is redox. Double replacement: two compounds exchange partners, which covers many precipitations, neutralizations, and gas-evolution reactions, and is usually not redox. Combustion of a hydrocarbon is combination with oxygen and is redox, often listed as its own type because the products are CO₂ and H₂O when oxygen is plentiful.
A reaction can wear more than one label. Acid plus carbonate is double replacement and gas-evolution. Use the label that answers the question being asked. A flowchart: is an element appearing or disappearing into a compound? Think redox and maybe single replacement or combination. Are two aqueous salts swapping? Think double replacement and check solubility. Is there H⁺ and OH⁻? Think neutralization.
Keep these
- Combination, decomposition, single replacement, double replacement, combustion.
- Single replacement and combustion are redox. Double replacement usually is not.
- Use the classification that matches the question: partners, electrons, or gas.