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Types of Reactions

Four Basic Types of Chemical Reactions

  • Synthesis Reactions

    • Description: Elements are joined together.

    • General Form: A+XAXA + X \rightarrow AX$$A + X \rightarrow AX$$

    • 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: AXA+XAX \rightarrow A + X$$AX \rightarrow A + X$$

    • 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+BXAX+BA + BX \rightarrow AX + B$$A + BX \rightarrow AX + B$$ or BX+YBY+XBX + Y \rightarrow BY + X$$BX + Y \rightarrow BY + X$$

    • 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)AY+BXAX(aq) + BY(aq) \rightarrow AY + BX$$AX(aq) + BY(aq) \rightarrow AY + BX$$

    • 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.


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Types of Reactions

Four Basic Types of Chemical Reactions

  • Synthesis Reactions

    • Description: Elements are joined together.
    • General Form: A+XAXA + X \rightarrow AX
    • Example: 2H2+O22H2O2H2 + O2 \rightarrow 2H_2O
    • Two substances combine to form one new compound.
    • Reaction of pure elements with oxygen and sulfur (e.g., Fe+O2Fe2O3Fe + O2 \rightarrow Fe2O_3).
    • Reactions of metals with Halogens.
  • Decomposition Reactions

    • Description: A compound breaks into parts.
    • General Form: AXA+XAX \rightarrow A + X
    • Example: 2H2O2H2+O22H2O \rightarrow 2H2 + O_2
    • Examples to memorize:
      • Metal carbonates (e.g., CaCO3(s)+heatCaO(s)+CO2(g)CaCO3(s) + heat \rightarrow CaO(s) + CO2(g), 2NaHCO3(s)+heatNa2CO3(s)+H2O(l)+CO2(g)2NaHCO3 (s) + heat \rightarrow Na2CO3(s) + H2O(l) + CO_2 (g)).
      • Metal chlorates (2KClO3(s)+heat2KCl(s)+3O2(g)2KClO3(s) +heat \rightarrow 2KCl(s) + 3O2(g)).
      • Unstable Oxyacids (H2CO3(aq)CO2(g)+H2O(l)H2CO3(aq) \rightarrow CO2(g) + H2O(l ), H2SO3(aq)SO2(g)+H2O(l)H2SO3(aq) \rightarrow SO2 (g) + H2O (l)).
      • Ammonium hydroxide (ammonia water): NH4OHNH3(g)+H2O(l)NH4OH \rightarrow NH3 (g) + H_2O (l).
  • Single Replacement Reactions

    • Description: A single element replaces an element in a compound.
    • General Form: A+BXAX+BA + BX \rightarrow AX + B or BX+YBY+XBX + Y \rightarrow BY + X
    • Example: Zn+2HClH2+ZnCl2Zn + 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)AY+BXAX(aq) + BY(aq) \rightarrow AY + BX
    • Example: H2SO4+2NaOHNa2SO4+2H2OH2SO4 + 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.