Types of Chemical Reactions
1
If you add two substances together
sometimes you get a chemical reaction.
This is when a new substance is made.
It is very difficult to reverse the
reaction and get the original substances
back.
Signs that a chemical reaction has taken
place include a change in colour, heat
being given off or bubbles of gas being
made.
Adding acid to
alkali
Fireworks

Ice cream
melting
x

Driving a car

Boiling the kettle
x
frying an egg

Discuss in pairs which of
The changes that are not
these arex chemical reactions

x
chemical changes are called
Lighting a matchphysical changes
Burning a candle

Printing
x
Melting
candle wax
Dissolving sugar
in tea
Making
ice cubes
Ironing
clothes
x
x
Baking a cake
Launching
a space
rocket


Objectives


Define and give general equations for
synthesis, decomposition, singlereplacement, and double-replacement
reactions.
Classify a reaction as synthesis,
decomposition, single-replacement,
single-replacement, doublereplacement, or combustion.
4
Objectives



List three types of synthesis reactions
and six types of decomposition
reactions.
List four types of single-replacement
reactions and three types of doublereplacement reactions.
Predict the products of single reactions
given the reactants.
5
Background

Thousands of known chemical reactions
occur in various systems. Memorizing
the equations for so many chemical
reactions would be difficult. It is more
useful and realistic to classify reactions
according to various similarities and
regularities.
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Combustion
Decomposition
Double
Replacement
+
The 5 Types
of Reactions
Single
Replacement
Synthesis
Synthesis Reactions

In a synthesis reaction, also known as
composition reaction, two or more
substances combine to form a new
compound.
– General equation: A + X
AX.

Types of synthesis reactions:
– Reactions of elements with oxygen and sulfur.
– Reactions of metals with halogens.
– Synthesis reaction with oxides.
8
+
Synthesis Reaction
Synthesis reaction – 2 substances combine to form a single product
A + B  AB
+

2Mg(s) + O2(g) 2MgO(s)
Magnesium and oxygen combine to form magnesium oxide.
2H2(g)+ O2(g) 2H2O(l)
Hydrogen and oxygen combine to form dihydrogen monoxide
Look at the reactants represented below, which reaction
involves elements as reactants? Which reaction involves
compounds as reactants?
Synthesis reaction
A synthesis reaction
involves the combination
smaller molecules
Decomposition reaction
A decomposition reaction
involves the breaking apart
of larger molecules
Recognizing the types of reactants is key to
identifying the reaction type
LETS US LOOK AT TWO OF THE REACTION
TYPES:SYNTHESIS AND DECOMPOSITION
Synthesis Reactions
• Involve the combination
of smaller atoms and
/or molecules into
larger molecules.
• They are also called
combination reactions
• General formula
• A + B
AB
• If you see two
elements as reactants,
you know the reaction
has to be a sysnthesis
reaction
• Synthesis reactions can also involve combinations of
small molecules.
• For example, when ammonia and hydrogen chloride
vapours combine, they form a white smoke as solid
particles of ammonium chloride are formed.
Hydrogen chloride + ammonia
ammonium chloride
HCl + NH3
NH4Cl
Similarly, combination of water and carbon dioxide
molecules
Synthesis reaction
CO2 + H2O
H2CO3(aq)
TYPICAL EXAMPLE , RAINWATER

Examples of Reaction of Elements with
Oxygen and Sulfur:
– Forming Oxides and sulfides:
 2Mg(s)
+ O2(g)
 16Rb(s) + S8(s)
 8Ba(s) + S8(s)
 S8(s) + 8O2(g)
 C(s) + O2(g)
 2C(s) + O2(g)
 2H2(g) + O2(g)
2MgO(s)
8Rb2S(s)
8BaS(s)
8SO2(g)
CO2(g)
CO(g)
2H2O(l)
15
– Forming Oxides and sulfides:
 2Fe(s)
+ O2(g)
 4Fe(s) + 3O2(g)
2FeO(s)
2Fe2O3(s)
16

Reactions of Metals with Halogens
(most metals react with the halogens
(group 17) to form either ionic or
covalent compounds.
– Group 1 metals with Group 17 elements
 2Na(s)
+ Cl2(g)
 2K(s) + I2(g)
2NaCl(s)
2KI(s)
– Group 2 metals with Group 17 elements
 Mg(s)
+ F2(g)
 Sr(s) + Br2(l)
MgF2(s)
SrBr2(s)
17
– Fluorine is so reactive that it combines with
almost all metals:
 2Na(s)
+ F2(g)
2NaF(s)
 2Co(s) + F2(g)
2CoF3(s)
 U(s) +3F2(g)
UF6(g)
 Practical application with fluorine:
– Sodium fluorine added to municipal water supplies.
– Cobalt(III) fluoride is a strong fluorinating agent.
– Uranium(VI) fluoride is the first step in the production
of uranium for use in nuclear power plants.
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
Synthesis Reactions with Oxides
– Oxides of active metals react with water to
produce metal hydroxides - example

CaO(s) + H2O(l)
Ca(OH)2(s)
– Many oxides of nonmetals (upper right portion of
the periodic table) react with water to produce
oxyacids - example
SO2(g) + H2O(l)
H2SO3(aq)
 this reacts with oxygen to produce sulfuric acid
2H2SO3(aq) + O2(g)
2H2SO4(aq)

– Certain metal oxides and nonmetal oxides react
with each other in synthesis reaction to form salts.
CaO(s) + SO2(g)
CaSO3(s)
19
Decomposition Reactions

In a decomposition reaction, a single
compound undergoes a reaction the
produces two or more products.
– General equation AX
A+X
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Decomposition Reactions
• It involve the splitting of • Example, electrolysis of
a large molecule into
water uses electricity to
elements or smaller
split water molecules
molecules.
into their elements
water hydrogen + oxygen
• General formula
H2O
H 2 + O2
AB
A+ B
2H2O
2H2 + O2
+
Decomposition Reaction
Decomposition reaction – A single compound breaks down
into 2 or more products.
AB  A + B
 +
2H2O2(aq) O2(g)+ 2H2O(l)
Hydrogen peroxide decomposes into oxygen gas and dihydrogen
monoxide.
2NaCl(s)  2Na(s) + Cl2(g)
Sodium chloride decomposes into sodium and chlorine gas.

Types of decomposition reactions
– Decomposition of Binary Compounds
– Decomposition of Metal Carbonates
– Decomposition of Metal Hydroxides
– Decomposition of Metal Chlorates
– Decomposition of Acids

Decomposition of Binary Compounds
electricity
– 2H2O(l)
2H2(g) + O2(g) (called electrolysis)
2HgO(s)
2Hg(l) + O2(g)
23

Decomposition of Metal Carbonates
– CaCO3(s)

Decomposition of Metal Hydroxides
– Ca(OH)2(s)

CaO(s) + H2O(g)
Decomposition of Metal Chlorates
– 2KClO3(s)

CaO(s) + CO2(g)
2KCl(s) + 3O2(g)
Decomposition of Acids
– H2CO3(aq)
– H2SO4(aq)
CO2(g) + H2O(l)
SO3(g) + H2O(l)
24
Single-Replacement Reactions

In a single-replacement reaction, also
know as a displacement reaction, one
element replaces a similar element in a
compound.
– A + BX
– Y + BX
AX + B or
BY + X
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Single Displacement Reactions
Mg + AgNo3 Ag + Mg(NO3)2
• Are chemical changes
that involve an element
Mg + 2AgNO3 2Ag + Mg(NO3)2
and a compound as
reactants.
• One element displaces or
replaces another
element from the
compound.
• Example, when
magnesium ribbon is
placed in a solution of
silver nitrate
+
Single Replacement Reaction
Single Replacement reaction – A single element takes the
place of another element in a compound.
A + BC  C + AB
+

+
AgNO3(aq) + Cu(s)  Ag(s) + CuNO3(aq)
Copper replaces silver in silver nitrate to copper (I) nitrate and silver.
Zn(s) + 2HCl(aq)  H2(g) + ZnCl2(aq)
Zinc replaces hydrogen in hydrogen chloride to yield hydrogen gas and zinc chloride.


Types of single-replacement reactions
– Replacement of a Metal in a Compound by
Another Metal
– Replacement of Hydrogen in Water by a
Metal
– Replacement of Hydrogen in Acid by a Metal
– Replacement of Halogens
Replacement of a Metal in a Compound by
Another Metal.
– A more active metal will replace a less active metal.
– 2Al(s) + 3Pb(NO3)2(aq)
3Pb(s) + 2Al(NO3)3(aq)
28

Replacement of Hydrogen in Water by a
Metal
– The most-active metals such as those in Group 1,
react vigorously with water to produce metal
hydroxides and hydrogen.
– example 2Na(s) + 2H2O(l)
2NaOH(aq) + 4H2(g)
– example 3Fe(s) + 4H2O(g)
Fe3O4(s) + 4H2(g)
(Less-active metals react with steam to form a metal oxide
and hydrogen gas)

Replacement of Hydrogen in an Acid by a Metal
– The more-active metals react with certain acidic
solutions replacing the hydrogen in the acid.
– example Mg(s) + 2HCl(aq)
H2(g) + MgCl2(ag)
29

Replacement of Halogens
– One halogen replaces another halogen in a
compound. Fluorine is the most-active halogen
and can replace any other halogen in their
compounds.
– Cl2(g) + 2KBr(aq)
2KCl(aq) + Br2(l)
– F2(g) + 2NaCl(aq)
2NaF(aq) + Cl2(s)
30
Double-Replacement Reactions

In double-replacement reactions, the ions of two
compounds exchange places in an aqueous solution
to form two new compounds.
– General equation AX + BY
AY + BX

Formation of a Precipitate
– The formation of a precipitate occurs when the
cations of one reactant combine with the anions of
another reactant to form an insoluble or slightly
soluble compound.
– 2KI(aq) + Pb(NO3)2(aq)
PbI2(s) + 2KNO3(aq)
31

Formation of a Gas
– In some double-replacement reactions, one of the
products in an insoluble gas that bubbles out of
the mixture.
– FeS(s) + 2HCl(aq)
H2S(g) + FeCl2(aq)

Formation of Water
– In some double-replacement reactions, a very
stable molecular compound, such as water, is one
of the products.
– HCl(aq) + NaOH(aq)
NaCl(aq) + H2O(l)
32
+
Double Replacement Reaction
Double Replacement reaction – Elements in 2 compounds
switch places to form 2 new compounds.
AB + CD  AD + CB
+
+

HCl(aq) + NaOH(aq)  HOH(l) + NaCl(aq)
Hydroxide and chlorine switch places to hydrogen hydroxide (water) and sodium chloride
Na2S(aq) + Zn(NO3)2(aq)  2NaNO3(aq) + ZnS (s)
Sulfur and nitrate switch places to form sodium nitrate and zinc sulfide.
Combustion Reactions

In a combustion reaction, a substance
combines with oxygen, releasing a large
amount of energy in the form of light
and heat.
– 2H2(g) + O2(g)
2H2O(g)
– C3H8(g) + 5O2(g)
3CO2(g) + 4H2O(g)
34
+
Combustion Reaction
Combustion reaction – A hydrocarbon (H and C) burn in oxygen to
produce water and carbon dioxide. Heat is given off as energy.
CxHx + O2  H2O + CO2 + heat
CH4(g) + 2O2(g)  2H2O (l) + CO2(g)
Methane burns in oxygen to produce water and carbon dioxide.
C12H22O11(s) + 12O2(g)  11H2O(l) + 12CO2(g)
Sucrose burns in oxygen to produce water and carbon dioxide.
Section Review


List five types of chemical reactions.
Complete and balance each of the following
reactions identified by type:
–
–
–
–
–
synthesis: ______
Li2O
decomposition: Mg(ClO3)2
______
single-replacement: Na + H2O
______
double-replacement: HNO3 +Ca(OH)2
combustion: C5H12 + O2
______
36
Section Review

Classify each of the following reactions:
–
–
–
–
–
–
–
N2(g) + 3H2(g)
2Li(s) + 2H2O(l)
2NaNO3(s)
2C6H14(l) + 19O2(g)
NH4Cl(s)
BaO(s) + H2O(l)
AgNO3(aq) + NaCl(aq)
2NH3(g)
2LiOH(aq) + H2(g)
2NaNO2(s) + O2(g)
12CO2(g) +14H2O(l)
NH3(g) + HCl(g)
Ba(OH)2(aq)
AgCl(s) + NaNO3(aq)
37