Classify 25 real balanced equations into the 5 standard reaction types: synthesis, decomposition, single replacement, double replacement, and combustion.
Correctly classifying a chemical reaction into one of five standard types is a foundational AP Chemistry Unit 4 skill that pays off throughout the course — knowing a reaction's type immediately tells you what kind of products to expect, before you've even balanced the equation.
Synthesis (combination) reactions combine two or more simpler substances into one more complex product: A + B → AB. Decomposition reactions run this in reverse, breaking one compound into two or more simpler products: AB → A + B, as seen when limestone (CaCO3) decomposes under heat into CaO and CO2.
Single replacement reactions occur when one element displaces another element from a compound: A + BC → AC + B, following activity series rules that predict whether the displacement actually occurs — zinc metal reacting with hydrochloric acid (Zn + 2HCl → ZnCl2 + H2) is a textbook single replacement, since zinc is more reactive than hydrogen and displaces it. Double replacement reactions swap the cations (or anions) between two ionic compounds: AB + CD → AD + CB, and typically proceed forward only when a precipitate, gas, or water forms — a solubility-rules judgment call.
Combustion reactions involve a fuel (usually a hydrocarbon) reacting with O2 to produce CO2 and H2O (for complete combustion) plus a large release of energy — recognizable by O2 always appearing as a reactant regardless of what specific fuel is burning. The industrial Haber process (N2 + 3H2 → 2NH3) is a synthesis reaction of major real-world significance, producing the ammonia that underlies most nitrogen fertilizer production worldwide.
Some reactions genuinely overlap categories or resist easy classification, and recognizing when a reaction is, for example, both a combustion and technically also fits no other category cleanly is itself part of building real classification fluency rather than pattern-matching on superficial equation shape.
This classifier presents 25 real balanced equations, asks you to identify the reaction type, and gives instant feedback with explanation for each — reinforcing the classification logic through repetition rather than memorized examples alone.