Types of Reactions

Four Basic Types of Chemical Reactions

• Synthesis Reactions

  • Description: Elements are joined together.
  • General Form: A + X \rightarrow AX
  • Example: 2H2 + O2 \rightarrow 2H_2O
  • Two substances combine to form one new compound.
  • Reaction of pure elements with oxygen and sulfur (e.g., Fe + O2 \rightarrow Fe2O_3).
  • Reactions of metals with Halogens.

• Decomposition Reactions

  • Description: A compound breaks into parts.
  • General Form: AX \rightarrow A + X
  • Example: 2H2O \rightarrow 2H2 + O_2
  • Examples to memorize:
    • Metal carbonates (e.g., CaCO3(s) + heat \rightarrow CaO(s) + CO2(g), 2NaHCO3 (s) + heat \rightarrow Na2CO3(s) + H2O(l) + CO_2 (g)).
    • Metal chlorates (2KClO3(s) +heat \rightarrow 2KCl(s) + 3O2(g)).
    • Unstable Oxyacids (H2CO3(aq) \rightarrow CO2(g) + H2O(l ), H2SO3(aq) \rightarrow SO2 (g) + H2O (l)).
    • Ammonium hydroxide (ammonia water): NH4OH \rightarrow NH3 (g) + H_2O (l).

• Single Replacement Reactions

  • Description: A single element replaces an element in a compound.
  • General Form: A + BX \rightarrow AX + B or BX + Y \rightarrow BY + X
  • Example: Zn + 2HCl \rightarrow H2 + ZnCl2
  • Replacement of:
    • Metal Cation replacement (Metals by another metal, Hydrogen in water by a metal, Hydrogen in an acid by a metal).
    • Halogens anion replacement by more active halogens.

• Double Replacement Reactions

  • Description: An element from each of two compounds switch places.
  • General Form: AX(aq) + BY(aq) \rightarrow AY + BX
  • Example: H2SO4 + 2NaOH \rightarrow Na2SO4 + 2H_2O
  • The ions of two compounds exchange places in an aqueous solution to form two new compounds.
  • One of the products must be a precipitate, a gas, or water.