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.
Double Displacement (or Replacement)
Reactions
pp. 220, 223
NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)
Fig. 8-18, p. 221
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.
Double Displacement (or
Replacement) Reactions
• ANSWERS
1. MgSO4 + 2 LiOH  Mg(OH)2 + Li2SO4
Exchange cations
2. Pb(NO3)2 + Na2CO3  PbCO3 + 2 NaNO3
3. 2 HNO3 + Ba(OH)2  Ba(NO3)2 + 2 H2O
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)
Exchange cations
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)
Table 9-3, p. 252
Fig. 9-13, p. 253
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.
Single Displacement (or Replacement)
Reactions
pp. 218, 220
Fig. 8-15, p. 218
Single Displacement (or
Replacement) Reactions
PREDICT THE PRODUCT
1. Ca + HCl 
2. ZnBr2 + I2 
3. Cu + AgNO3 
Answers are on the next slide.
Single Displacement (or
Replacement) Reactions
ANSWERS:
1. Ca + 2 HCl  CaCl2 + H2
2. ZnBr2 + I2  ZnI2 + Br2
3. Cu + 2AgNO3  2Ag + Cu(NO3)2
Single-Replacement Redox Reactions
A reaction occurs when a piece of zinc is dipped into a
solution of copper (II) nitrate. Write the conventional
(molecular), ionic and net ionic equations.
Fig. 9-9, p. 245
Single-Replacement Redox
Reactions
• Conventional (Molecular) Equation
Zn(s) + Cu(NO3)2 (aq) → Zn(NO3)2(aq) + Cu(s)
• Ionic Equation
Zn(s) + Cu+2(aq) + NO3- (aq) → Zn+2(aq) + NO3- (aq) + Cu(s)
• Net Ionic Equation
Zn(s) + Cu+2(aq) → Zn+2(aq) + Cu(s)
Table 9-2, p. 245
Single-Replacement Redox
Reactions
• What happens if we place a piece of copper
metal into a solution of zinc nitrate?
• Evidence shows that copper is below zinc
on the Activity Series, therefore copper will
not replace zinc and no reaction occurs.
• Cu(s) + Zn(NO3)2(aq) → NR
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.
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.
Fig. 16-2, p. 459
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)
C
(s)
+ O2 (g) → CO2 (g)
Fig. 8-11, p. 214
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)
2H2O(l) → 2H2(g) + O2(g)
Fig. 8-13, p. 215
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)
(hint: balance the C’s first, followed by the H then the O’s)
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)
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.
COMMON GAS FORMATION
REACTIONS YOU SHOULD REMEMBER
• NH4OH → NH3 (g) + H2O (l)
• H2CO3 → CO2 (g) + H2O (l)
• H2SO3 → SO2 (g) + H2O (l)
Table 8-3, p. 223
GROUP STUDY PROBLEM # 17a
Write 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.
PRACTICE PROBLEMS # 17a
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.
3 Mg (s) + N2 (g)  Mg3N2 (s); combination, redox
2. An aqueous solution of soluble aluminum nitrate is mixed with
aqueous sodium hydroxide to produce insoluble aluminum hydroxide
and a sodium nitrate solution.
Al(NO3)3 (aq) + 3NaOH (aq)  Al(OH)3(s) + 3NaNO3(aq) ; ppt, DD
3. Solid potassium sulfite is added to hydrochloric acid to produce sulfur
dioxide, water, and potassium chloride.
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)
4. Acetic acid reacts with calcium hydroxide to produce calcium acetate
and water.
2 HC2H3O2 (aq) + Ca(OH)2 (aq)  Ca(C2H3O2)2 (aq) + 2H2O (l) ; DD, neutralization
5. Lithium metal is dropped in water to produce lithium hydroxide and
hydrogen gas. 2Li (s) + 2H2O(l)  2LiOH (aq) + H2 (g); SD, redox
GROUP STUDY PROBLEM # 17b
PREDICT THE PRODUCT THEN WRITE A BALANCED EQUATION FOR EACH REACTIONS.
1. The reaction between lead (II) acetate and ammonium carbonate solutions
results in the formation of a white solid.
2. An zinc metal wire is dipped in hydrobromic acid.
3. The decomposition of sulfurous acid.
4. Sodium hydroxide solution is added to sulfuric acid.
5. Solid tin(II) sulfide is added to hydroiodic acid.
PRACTICE PROBLEMS # 17b
PREDICT THE PRODUCT THEN WRITE A BALANCED EQUATION FOR EACH REACTIONS.
1. Cadmium (II) iodide solution is added to aqueous potassium
phosphate.
3 CdI2 (aq) + 2 K3PO4 (aq)  Cd3(PO4)2 (s) + 6 KI (aq)
2. Magnesium hydroxide solution is mixed with phosphoric acid.
3 Mg(OH)2 (aq) + 2 H3PO4 (aq)  Mg3(PO4)2 (aq) + 6 H2O (l)
3. The decomposition of carbonic acid.
H2CO3 (aq)  CO2 (g) + H2O (l)
4. The combustion of methanol, CH3OH.
2 CH3OH (l) + 3 O2 (g)  2 CO2 (g) + 4 H2O (l)
5. Solid cadmium reacts with a copper(II) sulfate solution.
Cd (s) + CuSO4 (aq)  Cu (s) + CdSO4 (aq)