Redox Reactions
Synthesis
Decomposition
Single Replacement
Combustion
objective
I can classify redox
reactions so I can
recognize patterns of
chemical behavior and
predict the products of
reactions.
Redox Reaction Review
• In an oxidation – reduction
reaction (or Redox
reaction), electrons are lost
by one element and gained
by another element.
• Reactions that involve
elements as reactants or
products are always redox.
EX. Mg (s) + O2 (g)  MgO(s)
Which of the following is a redox reaction?
A.
B.
C.
D.
E.
2K(s) + Cl2(g) → 2KCl(s)
H2O2(aq) → H2O(l) + O2(g)
2Al(s) + 3Cu(SO4)(aq) → 3Cu(s) + Al2(SO4)3(aq)
CH4(g) + O2(g) → CO2(g) + 2H2O(l)
all of the above are redox reactions
Redox Reactions
• We classify chemical reactions so that we can
recognize patterns of chemical behavior, and
predict the products that will form.
• The following four types of reactions are all
considered Redox Reactions.
1.
2.
3.
4.
Synthesis
Decomposition
Single Replacement
Combustion
A + B  AB
AB  A + B
A + BC  B + AC
CxHy + O2  CO2 + H2O
Synthesis Redox Reaction
A + B  AB
• two or more substances combine to form a
single substance.
• The two reactants are frequently a Metal and a
non-Metal.
• The product that they form is then a(n) ionic
compound.
• To write the correct formulas for ionic
compounds, we use the criss-cross method.
Synthesis Redox Reaction
A. Group A metals and a nonmetal react
with each other to produce a compound
made up of a metal cation and a nonmetal
anion.
__K + __Cl2  ________
__K + __Cl2  __KCl
2K +
Cl2  2KCl
Synthesis Redox Reaction
A. Group A metals and a nonmetal react
with each other to produce a compound
made up of a metal cation and a nonmetal
anion.
__K + __Cl2  ________
__K + __Cl2  __KCl
2K +
Cl2  2KCl
Synthesis Redox Reaction
B. More than one product is also possible
when a transition metal and a nonmetal
react.
Fe + S  FeS
iron(II) sulfide
2Fe + 3S  Fe2S3
iron(III) sulfide
Synthesis Redox Reaction
C. When two nonmetals react by synthesis,
more than one product is often possible.
S + O2  SO2
sulfur dioxide
2S + 3O2  2SO3
sulfur trioxide
Which of the following
represents a synthesis
reaction?
A.
B.
C.
D.
AB  A + B
A + BC  B + AC
A + B  AB
AB + CD  CB + AD
Which of these is a synthesis redox reaction?
A. CH4(g) + O2(g) → CO2(g) + 2 H2O(l)
B. 2H2O2(aq) → 2H2O(l) + O2(g)
C. 2K(s) + Cl2(g) → 2KCl(s)
Decomposition Redox Reaction
AB  A + B
• In a decomposition reaction, a single compound
is broken down into two or more products.
– The reactant: a single compound
– The products: more than one element or compound.
• Most decomposition reactions require a catalyst
in the form of a chemical, heat, light, or
electricity.
TNT C7H5N3O6
TNT is one of the most commonly used explosives
for military and industrial applications.
2 C7H5N3O6(s) → 3 N2(g) + 5 H2(g) + 12 CO(g) + 2 C(s)
Which of these is a decomposition reaction?
A. CH4(g) + O2(g) → CO2(g) + 2 H2O(l)
B. 2H2O2(aq) → 2H2O(l) + O2(g)
C. 2K(s) + Cl2(g) → 2KCl(s)
Single Replacement
Combustion
REDOX REACTIONS PART II
Single-Replacement Reactions
A + BC  B + AC
• A metal element replaces a second metal
element in the compound.
– “A replaces B”
• AC and BC are ionic compounds
Example:
3 Mg (s) + 2 AlCl3 (aq)  2 Al (s) + 3 MgCl2 (aq)
Which of the following represents
a single replacement reaction?
A.
B.
C.
D.
AB  A + B
A + BC  B + AC
A + B  AB
AB + CD  CB + AD
Which of the following is a
single replacement redox reaction?
A.
B.
C.
D.
E.
2 K(s) + Cl2(g) → 2 KCl(s)
H2O2(aq) → H2O(l) + O2(g)
2 Al(s) + 3 Cu(SO4)(aq) → 3 Cu(s) + Al2(SO4)3(aq)
CH4(g) + O2(g) → CO2(g) + 2 H2O(l)
none of the above
Single Replacement Reactions
A + BC  B + AC
Not all single replacement reactions can
occur.
Whether one metal will replace another
metal from a compound can be
determined by the relative reactivities of
the two metals.
Single Replacement Reactions
A + BC  B + AC
A reactive metal will only replace a
metal listed below it in the Activity
Series.
Mg(s) + Zn(NO3)2(aq) 
Mg(s) + Li(NO3)(aq) 
Single Replacement Reactions
A + BC  B + AC
A reactive metal will only replace a
metal listed below it in the Activity
Series.
Mg(s) + Zn(NO3)2(aq)  Mg(NO3)2(aq) + Zn(s)
Mg(s) + Li(NO3)(aq)  no reaction
Which of these is higher on the activity
series?
A. calcium
B. magnesium
Which of these is higher on the activity
series?
A. hydrogen
B. magnesium
A reactive metal will only replace a metal
listed below it in the Activity Series.
Which of these reactions will NOT occur?
A. Mg(s) + 2HCl(aq)  H2(g) + MgCl2(aq)
B. H2(g) + MgCl2(aq)  Mg(s) + 2HCl(aq)
Can this single replacement reaction occur?
“aluminum reacts with rust to produce iron and
aluminum oxide”
2Al(s) + Fe2O3(s)  2Fe(s) + Al2O3(s)
A. Yes
B. No
CxHy + O2  CO2 + H2O + energy
A.
In a combustion reaction, a compound reacts
with oxygen to produce energy as heat, light
or electricity.
B.
Reactants: hydrocarbons (compounds of
hydrogen and carbon) and oxygen
Products: carbon dioxide and water
Which of these is always the
products of a combustion reaction?
A. oxygen and heat
B. hydrogen and oxygen
C. water and carbon dioxide
D. carbon dioxide and oxygen
You observe the combustion of
butane C4H10…….
Which of these reactants must also
be present?
A. water
B. carbon dioxide gas
C. oxygen gas
D. hydrogen gas
C4H10
Combustion reaction Example:
CH4 (g) + 2O2 (g)  CO2 (g) + 2H2O
Hydrocarbon molecule examples CxHy
methane CH4
octane C8H18
propane C3H8
Which of the following represents
a combustion redox reaction?
A.
B.
C.
D.
E.
F.
AB  A + B
A + BC  B + AC
HxCy + O2  CO2 + H2O
A + B  AB
AB + CD  CB + AD
none of the above
Which of these is a combustion
reaction?
A. C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(l)
B. 2H2O2(aq) → 2H2O(l) + O2(g)
C. 2K(s) + Cl2(g) → 2KCl(s)