Reaction types

	Vocabulary
	chemical change combination reaction decomposition displacement double displacement isomerization neutralization precipitation product reactant redox synthesis

Chemical reactions are often classified to highlight patterns in chemical behavior. In some cases, categorizing a reaction can allow its products to be predicted. Many chemical reactions fall into one of four broad classes: rearrangement, combination, decomposition, and displacement.

4 H2 + 4 Cl2		8 HCl

• Combination reactions build a compound from simpler compounds or elements.
  • General form: A + B C
  • Recognition: Usually a single product and several reactants
  • Synonyms: synthesis
  • Examples
    C₂H₄(g) + H₂O(g) C₂H₅OH(g)
    H₂(g) + ½ O₂(g) H₂O(l)
    
• Decomposition reactions break a compound into simpler fragments.

  4 H2O2		4 H2O + 2 O2

  • General form: C A + B
  • Recognition: Usually a single reactant and several products
  • Examples
    H₂CO₃(aq)H₂O(l) + CO₂(g)
    CaCO₃(s)CaO(s) + CO₂(g)
    2NH₄NO₃(s)2N₂(g) + 4H₂O(g) + O₂(g)
    2 H₂O(l) 2 H₂(g) + O₂(g)
• Rearrangement reactions making and breaking bonds within a compound.

  HOONO		HNO3

  • General form: A B
  • Recognition: reactant and product have same molecular formula but different structural formulas
  • Synonyms: isomerization
• Displacement reactions involve replacement or swapping of parts of a compound.
  • General forms
    • single displacement: A + BC AB + C
    • double displacement: AB + CD AD + BC
  • Features
    • # of reactants is usually equal to the # of products
      
    • atoms or ions migrate from one compound to another
  • Synonyms: double displacement reactions are sometimes called "metathesis" reactions
  • Examples
    Zn(s) + 2 HCl(aq)ZnCl₂(aq) + H₂(g)
    Mg(s) + CuCl₂(aq)MgCl₂(aq) + Cu(s)
    NaOH(aq) + HCl(aq) H₂O(l) + NaCl(aq)
    BaCl₂(aq) + Na₂SO₄(aq) = BaSO₄(s) + 2 NaCl(aq)
    
These additional categories include many important chemical reactions. Learn to recognize them.
• Neutralization reactions: one compound acquires H⁺ from another
  • Features
    • usually double displacement reactions (but not always)
    • one reactant must be an acid (have detachable H⁺ ions)
    • one reactant must be a base (accept H⁺ taken from the acid)
    • water is a product if the base is a hydroxide
  • Synonyms: acid-base reaction, proton transfer reaction
  • Examples
    H₂SO₄(aq) + 2 NaOH(aq) Na₂SO₄(aq) + 2 H₂O(l)
    KOH + HC₂H₃O₂(aq) H₂O(l) + KC₂H₃O₂(aq)
    NH₃(aq) + HCl(aq) NH₄Cl(aq)
• Precipitation reactions: solid product is formed in a liquid or gaseous environment.
  • Features
    • usually displacement reactions that form an insoluble ionic compound
  • Examples
    AgNO₃(aq) + NaCl(aq) = AgCl(s) + NaNO₃(aq)
    SrCl₂(aq) + Na₂SO₄(aq) = SrSO₄(s) + 2 NaCl(aq)
    
• Redox reactions occur when one compound acquires electrons from another
  • Features
    • at least one reactant loses electrons
    • at least one reactant gains electrons
  • Examples
    
    • combustion reactions (fuel reacting with oxygen)
      2 C₂H₆(g) + 7 O₂(g) 4 CO₂(g) + 6 H₂O(g)
      
    • combination of elements 2 Na(s) + Cl₂(g) 2 NaCl(s)
      
    • displacement of hydrogen from water or acids 2 Na(s) + 2 H₂O(l) 2 NaOH(aq) + H₂(g)
      Zn(s) + 2 HCl(aq)ZnCl₂(aq) + H₂(g)
      
    • displacement of metal ions from solution
      Mg(s) + CuCl₂(aq)MgCl₂(aq) + Cu(s)
      Zn(s) + 2 AgNO₃(aq)Zn(NO₃)₂(aq) + 2Ag(s)
      



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General Chemistry Online! Reaction types

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Last Revised 06/16/05.URL: http://antoine.frostburg.edu/chem/senese/101/reactions/print-types.shtml