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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.
longrightarrow
4 H2 + 4 Cl28 HCl
  • Combination reactions build a compound from simpler compounds or elements.
    • General form: A + B rightarrow C
    • Recognition: Usually a single product and several reactants
    • Synonyms: synthesis
    • Examples
      C2H4(g) + H2O(g)rightarrow C2H5OH(g)
      H2(g) + ½ O2(g) rightarrow H2O(l)
  • Decomposition reactions break a compound into simpler fragments.
    longrightarrow
    4 H2O24 H2O + 2 O2
    • General form: C rightarrow A + B
    • Recognition: Usually a single reactant and several products
    • Examples
      H2CO3(aq)rightarrowH2O(l) + CO2(g)
      CaCO3(s)rightarrowCaO(s) + CO2(g)
      2NH4NO3(s)rightarrow2N2(g) + 4H2O(g) + O2(g)
      2 H2O(l) rightarrow 2 H2(g) + O2(g)
  • Rearrangement reactions making and breaking bonds within a compound.
    longrightarrow
    HOONOHNO3
    • General form: A rightarrow 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 rightarrow AB + C
      • double displacement: AB + CD rightarrow 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)rightarrowZnCl2(aq) + H2(g)
      Mg(s) + CuCl2(aq)rightarrowMgCl2(aq) + Cu(s)
      NaOH(aq) + HCl(aq) rightarrowH2O(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) rightarrow Na2SO4(aq) + 2 H2O(l)
      KOH + HC2H3O2(aq)rightarrow H2O(l) + KC2H3O2(aq)
      NH3(aq) + HCl(aq) rightarrow 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)rightarrow 4 CO2(g) + 6 H2O(g)
      • combination of elements 2 Na(s) + Cl2(g) rightarrow 2 NaCl(s)
      • displacement of hydrogen from water or acids 2 Na(s) + 2 H2O(l) rightarrow 2 NaOH(aq) + H2(g)
        Zn(s) + 2 HCl(aq)rightarrowZnCl2(aq) + H2(g)
      • displacement of metal ions from solution
        Mg(s) + CuCl2(aq)rightarrowMgCl2(aq) + Cu(s)
        Zn(s) + 2 AgNO3(aq)rightarrowZn(NO3)2(aq) + 2Ag(s)
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General Chemistry Online! Reaction types

Copyright © 1997-2005 by Fred Senese
Comments & questions to fsenese@frostburg.edu
Last Revised 06/16/05.URL: http://antoine.frostburg.edu/chem/senese/101/reactions/types.shtml