Types of Chemical Reactions

A. Combination Reaction

• What happens? Two or more substances combine to form one new substance.

• Example: CaO + H₂O → Ca(OH)₂
  (Quicklime + water → Slaked lime)

B. Decomposition Reaction

• What happens? One substance breaks into two or more simpler substances.

• Example: 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂
  (When lead nitrate is heated, it breaks down.)

C. Displacement Reaction

• What happens? A more reactive element kicks out a less reactive element from its compound.

• Example: Zn + CuSO₄ → ZnSO₄ + Cu
  (Zinc replaces copper because zinc is more reactive.)

D. Double Displacement Reaction

• What happens? Two compounds exchange parts (ions) to form new compounds.

• Example: Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
  (White solid BaSO₄ forms — this is called a precipitate.)

E. Redox Reaction

• What happens? One substance loses electrons (oxidation) and another gains electrons (reduction) — both happen in one reaction.

• Example: Zn + Cu²⁺ → Zn²⁺ + Cu
  (Zinc gives away electrons, and copper takes them.)