Chapter 6-2 Types of Chemical Reactions
Charcoal fuels BBQ grills
through combustion of
carbon. Release of energy
(heat or light) is an
important product in
combustion reactions
There are five basic types of reactions:
Combination -, Decomposition -,
Single-Replacement -, Double-Replacement -,
and Combustion Reactions.
(Not all reactions fit into this classifications)
1
Combination Reaction (Synthesis Reaction)
2 Mg + O2  2 MgO
Mg O2
O2-
Mg2+
2
In a synthesis (combination) reaction, two or more
substances combine to form a single substance
A + B + …  AB..
Examples:
Fe (s) + S(s)
 FeS (s)
iron (II) sulfide
SO2 (g) + H2O (l)  H2SO3 (aq) sulfurous acid
CaO(s) + H2O (l)  Ca(OH)2 (aq) calcium hydroxide
In a decomposition reaction, a single compound is
broken down into two or more products
AB..  A + B + ...
Example:
CaCO3 (s)  CaO (s) + CO2 (g)
(“opposite of synthesis or combination reaction)
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Explosion of dynamite is a powerful
decomposition reaction
4
Single-Replacement Reactions
Potassium +
water  potassium hydroxide + hydrogen
2 K (s) + 2 H2O (l)  2 KOH (aq) + H2 (g)
5
In a single-replacement reaction, one element replaces
a second element in a compound
AB + C  AC + B
Example:
Mg (s) + 2 AgNO3 (aq)  Mg(NO3)2 (aq) + 2 Ag (s) but
Mg (s) + 2 LiNO3 (aq)  no reaction
If one metal will displace another metal from a
compound can be determined by the relative reactivity
of two metals. The activity series of metals lists metals
in order decreasing reactivity.
A nonmetal can also displace another nonmetal
(usually halogens) reactivity decreases down group 7A.
6
Activity Series of Metals
One metal replaces
another metal
(or hydrogen)
Or one halogen
replaces another
halogen (F, Cl, Br, I)
* Metals from Li to Na
will replace H from acids
and water; from Mg to Pb
they replace H from acids
7
only
Double-Replacement Reactions
potassium carbonate + barium chloride  potassium chloride + barium carbonate
K2CO3 (aq) + BaCl2 (aq)  2 KCl (aq) + BaCO3 (s)
8
Double-Replacement Reactions involve an exchange of
positive ions between two reacting compounds
AB + CD  AD + DB
Examples:
NaS (aq) + Cd(NO3)2 (aq)  CdS (s) + 2 NaNO3 (aq)
NaCN (aq) + H2SO4 (aq)  2 HCN (g) + Na2SO4 (aq)
Ca(OH)2 (aq) + 2HCl (aq)  CaCl2 (aq) + 2 H2O (l)
Generally a reaction between two ionic compounds,
with one product precipitating from the solution
(a solid being formed) or escaping as a gas, or water
being formed as one product.
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Combustion Reactions
methane
+ oxygen  carbon dioxide + water
CH4 (g) +
2 O2 (g)  CO2 (g) + 2 H2O 10(g)
In a combustion reaction an element or compound
reacts with oxygen, usually releasing energy in form
of heat or light.
(A + O2  AO + ... + energy)
CnHm + O2  CO2 + H2O + energy
Examples:
2 C2H6(g) + 7 O2(g)  4 CO2(g) + 6 H2O(g) + energy
2 CH3OH(l) + 3 O2(g)  2 CO2(g) + 4 H2O(g) + energy
C (s) + O2 (g)  CO2(g) + energy
The complete combustion of a hydrocarbon CnHm
produces carbon dioxide and water. Without sufficient
oxygen, carbon monoxide and carbon (soot) may be
formed.
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Types of Reactions
1. A + B
 AB
2.
 A +B
AB
3. A + BC

AC + B
4. AB + CD  AD + CB
5.
CnHm + O2  CO2 + H2O
12
Ionic Charges (oxidation numbers) of main group elements
+1 +2
+3 V. -3 -2
-1
0
Vary
13
Most elements are composed of atoms,
but 7 exist as diatomic molecules:
Nitrogen N2, Oxygen O2, Fluorine F2,
Chlorine Cl2, Bromine Br2, Iodine I2,
and Hydrogen H2,
start at 7, make a 7, plus hydrogen
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Activity Series of Metals
Single Replacement:
One metal replaces
another metal
(or hydrogen)
Or one halogen
replaces another
halogen (F, Cl, Br, I)
* Metals from Li to Na
will replace H from acids
and water; from Mg to Pb
they replace H from acids
15
only
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6.3 Nature of Reactions
Collision Theory
In a chemical reaction the particles involved
must collide with enough force to initiate the
chemical change. The energy needed for a
reaction to occur is called activation energy.
The rate of a reaction can often be increased
by increasing temperature (energy) or
concentration (higher probability of collision).
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18
19
The reaction rate (speed) can be
changed by changing factors like
temperature,
concentration,
or by adding
a catalyst (to speed up) or
an inhibitor (to slow down).
…also surface area, particle size etc.
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21
A reversible reaction can change
direction and the products react
back into the reactants
(example rechargeable batteries).
A double arrow is used instead of
the usual left –to –right arrow) .
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Dynamic Equilibrium
Reactants and products are formed at the same
rate (no net change of the chemical composition)
H2(g) + N2(g)
NH3(g)
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The ratio of reactants and products in the
equilibrium (how much of each) is not
necessary equal (1:1).
Le Chatelier’s principle
The equilibrium can be shifted, meaning
pushed more to one side by changing
reaction conditions, especially concentration
and temperature.
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Activation energy with and without catalyst
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