Five families that cover almost everything
Most chemical reactions you meet at school are one of five patterns. Recognise the pattern and you can usually predict the products, even before you balance.
Synthesis (combination)
Two or more reactants combine into a single product.
Mg + S → MgS
Decomposition
A single compound breaks into two or more products. Often driven by heat or current.
2 KClO₃ → 2 KCl + 3 O₂
Single replacement
A more reactive element kicks a less reactive one out of a compound. Whether it happens depends on the activity series.
Cu + 2 AgNO₃ → Cu(NO₃)₂ + 2 Ag
Double replacement
Cations and anions swap partners in solution. Driven by an insoluble precipitate, gas or weak electrolyte.
HCl + NaOH → NaCl + H₂O
Combustion
A hydrocarbon (or other fuel) burns in oxygen to give carbon dioxide and water; releases heat and light.
2 C₂H₆ + 7 O₂ → 4 CO₂ + 6 H₂O
Acid–base (neutralization)
A subtype of double replacement. Produces water and a salt.
H₂SO₄ + 2 KOH → K₂SO₄ + 2 H₂O
Redox (electron transfer)
Any reaction where atoms change oxidation state. Combustion and single-replacement are usually redox.
Zn + Cu²⁺ → Zn²⁺ + Cu
Precipitation
A specific double replacement that yields an insoluble solid. Use solubility rules to predict.
Hands-on tools
Classify any equation; predict whether a single-replacement will go using the activity series.
Reaction classifier
Enter an equation. The classifier matches the structural pattern.
Activity series — will it react?
Pick element A and the metal in the compound BC. The series predicts whether A + BC → AC + B will run.
Activity series of metals (most reactive on top)
Solubility rules — soluble or precipitate?
Pick a cation and anion. The rule set predicts solubility in water at 25 °C.
Solubility rules
- Always soluble: alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) and ammonium (NH₄⁺); also nitrates (NO₃⁻), acetates (C₂H₃O₂⁻) and chlorates (ClO₃⁻).
- Halides (Cl⁻, Br⁻, I⁻): soluble — except with Ag⁺, Pb²⁺, Hg₂²⁺.
- Sulfates (SO₄²⁻): soluble — except with Ba²⁺, Sr²⁺, Pb²⁺, Ca²⁺ (slightly soluble).
- Hydroxides (OH⁻) and sulfides (S²⁻): generally insoluble — except with alkali metals and (for sulfides) Ca²⁺, Sr²⁺, Ba²⁺.
- Carbonates (CO₃²⁻), phosphates (PO₄³⁻): generally insoluble — except with alkali metals and ammonium.
Quiz
Flashcards
Tap a card to flip. ← / → keys to navigate.
Daily challenge
Five reactions to classify. Same set worldwide, refreshes at midnight UTC.
For teachers
Print-ready worksheet, answer key, teaching tips and standards alignment.
Teaching tips
Standards alignment
Reference
Glossary
Diatomic elements (always paired in nature)
Photo gallery — reactions in action
Images sourced from Wikipedia.