4.7 Types of Chemical Reactions

Classifying reactions by pattern

Chemical reactions can be sorted by the pattern of atom rearrangement: synthesis (A + B → AB), decomposition (AB → A + B), single replacement (A + BC → AC + B), and combustion (fuel + O₂ → CO₂ + H₂O). Recognizing the pattern helps predict products before balancing the equation.

Precipitation reactions

In a precipitation reaction, two soluble ionic compounds in aqueous solution swap ions to form an insoluble solid (precipitate). Use solubility rules to predict whether a product will precipitate. The net ionic equation shows only the ions that actually combine, omitting spectator ions.

Acid–base and oxidation–reduction reactions

Acid–base reactions involve transfer of H⁺ (protons) from an acid to a base, often producing water and a salt (neutralization). Oxidation-reduction (redox) reactions involve transfer of electrons, changing oxidation states; one species is oxidized (loses electrons) while another is reduced (gains electrons).

Key terms

Synthesis reaction

Two or more substances combine to form a single product: A + B → AB.

Decomposition reaction

A single compound breaks down into two or more simpler substances: AB → A + B.

Precipitation reaction

Two soluble ionic compounds exchange ions in solution to form an insoluble solid (precipitate).

Redox reaction

A reaction involving electron transfer; one species is oxidized (loses electrons) and another is reduced (gains electrons).

Acid-base (neutralization) reaction

A reaction where an acid donates H⁺ to a base, typically producing water and a salt.

Try an AP-style question

What type of reaction is Zn + CuSO₄ → ZnSO₄ + Cu?

1. Precipitation
2. Acid–base
3. Redox
4. Decomposition only