Types of Reactions

Four Basic Types of Chemical Reactions

• Synthesis Reactions

  • Description: Elements are joined together.
  • General Form: $A + X \rightarrow AX$
  • Example: $2H<em>2 + O</em>2 \rightarrow 2H_2O$
  • Two substances combine to form one new compound.
  • Reaction of pure elements with oxygen and sulfur (e.g., $Fe + O<em>2 \rightarrow Fe</em>2O_3$).
  • Reactions of metals with Halogens.

• Decomposition Reactions

  • Description: A compound breaks into parts.
  • General Form: $AX \rightarrow A + X$
  • Example: $2H<em>2O \rightarrow 2H</em>2 + O_2$
  • Examples to memorize:
    • Metal carbonates (e.g., $CaCO<em>3(s) + heat \rightarrow CaO(s) + CO</em>2(g)$, $2NaHCO<em>3 (s) + heat \rightarrow Na</em>2CO<em>3(s) + H</em>2O(l) + CO_2 (g)$).
    • Metal chlorates ($2KClO<em>3(s) +heat \rightarrow 2KCl(s) + 3O</em>2(g)$).
    • Unstable Oxyacids ($H<em>2CO</em>3(aq) \rightarrow CO<em>2(g) + H</em>2O(l )$, $H<em>2SO</em>3(aq) \rightarrow SO<em>2 (g) + H</em>2O (l)$).
    • Ammonium hydroxide (ammonia water): $NH<em>4OH \rightarrow NH</em>3 (g) + H_2O (l)$.

• 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: $Zn + 2HCl \rightarrow H<em>2 + ZnCl</em>2$
  • 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: $H<em>2SO</em>4 + 2NaOH \rightarrow Na<em>2SO</em>4 + 2H_2O$
  • 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.