Double Displacement (or Replacement) Reactions

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Double Displacement (or Replacement) Reactions

• Also referred to as metathesis reaction
• The two compounds exchange ions to produce two
  new compounds. It is easier to simply remember
  that the cations ( ions) exchange anions (-
  ions).
• AB CD ? CB AD
• NOTE always write the cation first then the
  anion.
• Many reactions including precipitation and
  neutralization use the double displacement
  mechanism.

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Double Displacement (or Replacement) Reactions

• PREDICT THE PRODUCT BALANCE
• 1. MgSO4 LiOH ? ___________
• 2. Pb(NO3)2 Na2CO3 ? ____________
• 3. HNO3 Ba(OH)2 ? ___________

Answers are on the next slide.
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Double Displacement (or Replacement) Reactions

• ANSWERS
• 1. MgSO4 2 LiOH ? Mg(OH)2 Li2SO4
• 2. Pb(NO3)2 Na2CO3 ? PbCO3 2 NaNO3
• 3. 2 HNO3 Ba(OH)2 ? Ba(NO3)2 2 H2O

Exchange cations
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PRECIPITATION REACTION

• A reaction where an insoluble solid is formed
  during a reaction between two aqueous solutions.
• (aq) (aq) ? (aq) (s)
• 2KI(aq) Pb(NO3)2(aq) ? 2KNO3(aq) PbI2(s)
• NEUTRALIZATION REACTION
• A reaction between an acid and a base which
  results in the production of a salt and water.
• HA BOH ? (metal/nonmetal) H2O
• HNO3(aq) KOH(aq) ? KNO3(aq) H2O(l)

Exchange cations
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Single Displacement (or Replacement) Reactions

• One element reacts with a compound to produce a
  different element and a new compound.
• A BC ? AC B
• NOTE if the element is a metal, it will replace
  the cation.
• A BC ? C BA
• NOTE if the element is a nonmetal, it will
  replace the anion.
• Many reduction-oxidation reactions use the
  single displacement mechanism.

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Single Displacement (or Replacement) Reactions

• PREDICT THE PRODUCT
• 1. Ca HCl ?
• 2. ZnBr2 I2 ?
• 3. Cu AgNO3 ?

Answers are on the next slide.
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Single Displacement (or Replacement) Reactions

• ANSWERS
• 1. Ca 2 HCl ? CaCl2 H2
• 2. ZnBr2 I2 ? ZnI2 Br2
• 3. Cu 2AgNO3 ? 2Ag Cu(NO3)2

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Reduction-Oxidation Reactions

• A reaction in which electrons are transferred
  from one species to another.
• Oxidation means the loss of electrons
• Reduction means the gain of electrons
• Rusting is a redox reaction
• 4Fe (s) 3O2 (g) ? 2Fe2O3 (s)
• As a reactant Fe has a zero oxidation state but
  as a product (in Fe2O3) iron has a 3 oxidation
  state. Three electrons per atom had to be
  transferred (lost) in order for this to happen.
  Note that oxygen also changed from a zero
  oxidation state to a 2- oxidation state. Oxygen
  needed to gain 2 electrons per atom.

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Reduction-Oxidation Reactions

• Oxidation means the loss of electrons
• Reduction means the gain of electrons
• Electrochemistry involves redox Rx.
• Cu(s) 2AgNO3(aq) ? 2Ag(s) Cu(NO3)2(aq)
• The reactant Cu has a zero oxidation state (all
  elements have a zero oxidation state) but as a
  product, in Cu(NO3)2,the copper atom loses two
  electrons and has a 2 oxidation state. The
  other atom which acquired the electrons donated
  by copper is silver. As a reactant silver has a
  1 oxidation state then by gaining electrons from
  copper, the ions are turned into elemental silver
  with a zero oxidation state.
• The net effect of this reaction has metallic
  copper being oxidized to copper ions and silver
  ions being reduced to silver metal.

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COMBINATION REACTION

• A reaction in which two or more substances
  combine to form a single product.
• A B C ? ABC
• CaO(s) SO2(g) ? CaSO3(s)
• DECOMPOSITION REACTION
• A reaction in which a single compound reacts to
  give two or more substances, usually requiring a
  raise in temperature.
• ABC ? A B C
• 2KClO3(s) ? 2KCl(s) 3O2(g)

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COMBUSTION REACTION

• A reaction of a substance with oxygen, usually
  the rapid release of heat produces a flame.
• CH O2 ? CO2 H2O
• 2C4H10(g) 13O2(g) ? 8CO2(g) 10H2O(g)
• Many times in a combustion reaction, heat energy
  is given off. In chemical terms this is called
  an exothermic reaction. Thermochemistry is field
  of chemistry which studies the transfer of heat
  in a reaction.
• The thermodynamic equation representing this
  exothermic reaction is
• 2C4H10(g) 13O2(g) ? 8CO2(g) 10H2O(g)
  heat (in Joules)

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GAS FORMATION REACTIONS

• A reaction that produces a gas from reactants not
  in the gaseous state.
• 2 HCl (aq) ZnS (s) ? ZnCl2 (aq) H2S (g)
• Zn (s) 2 HCl (aq) ? ZnCl2 (aq) H2 (g)
• Many gas formation reactions involve two steps,
  first the double displacement reaction then the
  decomposition reaction of an unstable substance.
  
• Na2CO3 2HCl ? 2 NaCl H2CO3
• H2CO3 ? CO2 H2O
• Besides carbonic acid (H2CO3), sulfurous acid
  (H2SO3) also decomposes into SO2 and water.

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PRACTICE PROBLEMS Write the following as
balanced chemical equations then classify each
reaction.

• 1. Magnesium metal is combined with nitrogen at
  elevated temperatures to form magnesium nitride
  powder.
• 2. An aqueous solution of soluble aluminum
  nitrate is mixed with aqueous sodium hydroxide to
  produce insoluble aluminum hydroxide and a sodium
  nitrate solution.
• 3. Solid potassium sulfite is added to
  hydrochloric acid to produce sulfur dioxide,
  water, and potassium chloride.
• 4. Acetic acid reacts with calcium hydroxide to
  produce calcium acetate and water.
• 5. Lithium metal is dropped in water to produce
  lithium hydroxide and hydrogen gas.

3 Mg (s) N2 (g) ? Mg3N2 (s) combination, redox
Al(NO3)3 (aq) 3NaOH (aq) ? Al(OH)3(s)
3NaNO3(aq) ppt, DD
K2SO3 (s) 2HCl (aq) ? H2SO3 (aq) 2KCl (aq)
DD then H2SO3 (aq) ? H2O (l) SO2 (g)
decomposition overall Rx K2SO3 (s) 2HCl (aq)
? H2O (l) SO2 (g) 2KCl (aq)
2 HC2H3O2 (aq) Ca(OH)2 (aq) ? Ca(C2H3O2)2 (aq)
2H2O (l) DD, neutralization
2Li (s) 2H2O(l) ? 2LiOH (aq) H2 (g) SD, redox
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GROUP STUDY PROBLEMSWrite the following as
balanced chemical equations then classify each
reaction.

• 1. Solid mercuric oxide decomposes at high
  temperatures to form metallic mercury and oxygen.
• 2. Aqueous lead(II) nitrate reacts with aqueous
  magnesium bromide to produce the insoluble salt
  lead(II)bromide and soluble magnesium nitrate.
• 3. At room temperature, aqueous ammonium
  carbonate is added to hydrochloric acid to
  produce aqueous ammonium chloride, water and
  carbon dioxide.
• 4. Hydrochloric acid is poured over tin metal
  producing hydrogen gas and tin (IV) chloride.
• 5. The combustion of ethanol, C2H5OH, results in
  the production of carbon dioxide and water.