Chemical
Reactions
COME+BIN-E+SAT
-S+ION
DECORATE+M-RATE
+POSITION
DISH-H+PLACE
+MENTOL-OL
DEN-DN+X
+CHANGE
COMB+RUST-R
-ION
Types of Chemical Reactions
Decomposition
reactions
Displacement
reactions
Exchange
reactions
Chemical reaction- is
a process in which at
least one new
Combustion
Combination
substance is
reactions
reactions
produced a result of
chemical change.
Combination Reactions

Is a chemical reaction in which a single
product is produced from two (or more)
reactants.

X+Y
Elements as the reactant
Ca + S --> CaS
N2 + 3H2 --> 2NH3
XY
Compounds as the reactant
SO3 + H2O --> H2SO4
2NO + O2 --> 2NO2
Decomposition Reactions

Is a chemical reaction in which a single reactant is
converted into two (or more) simpler substances
(elements or compounds).

XY
Elements as the product
2CuO --> 2Cu + O2
2H2O --> 2H2 + O2
X +Y
Compounds as the product
CaCO3 --> CaO + CO2
2KClO3 --> 2KCl + 3O2
Displacement Reactions
Single-replacement

Is a chemical reaction in which an atom or molecule
displaces an atom or group of atoms from a
compound.

X + YZ
Y +XZ
Fe + CuSO4 --> Cu + FeSO4
Mg + Ni(NO3)2 --> Ni + Mg(NO3)2
Exchange Reactions
Double-replacement

Is a chemical reaction in which two substances
exchange parts with one another and form two
different substances.

AX + BY
AY + BX
AgNO3 + NaCl --> AgCl + NaNO3
2KI + Pb(NO3)2 --> 2KNO3 + PbI2
Combustion Reactions

Is a chemical reaction between a substance and
oxygen (usually fro air) that proceeds with the
evolution of heat and light (usually from a flame).
2C2H2 + 5O2 --> 4CO2 + 2H2O
CS2 + 3O2 --> CO2 + 2SO2
Combination reactions in which oxygen
reacts with another element to form a
single product are also combustion
reactions.
Classifying Chemical Reactions





Classify each of the following chemical reactions
as a combination,decomposition, displacement,
exchange, or combustion reaction.
1. 2KNO3 --> 2KNO2 + O2
2. Zn + 2AgNO3 --> Zn(NO3)2 + 2Ag
3. Ni(NO3)2 + 2NaOH --> Ni(OH)2 + 2NaNO3
4. 3Mg + N2 --> Mg3N2
THE CHEMICAL REACTION AND
ENERGY





Basic ideas of the kinetic molecular theory
Molecules and atoms in a reaction mixture are in
constant, random motion;
These molecules and atoms frequently collide with each
other.
Only some collision, those with sufficient energy, will
break bonds in molecules; and
When reactant bonds are broken, new bonds may be
formed and products result.




The statements of collision theory are
1. Molecular collision. Reactant particles must
interact (that is, collide) with one another
before any reaction can occur.
2. Activation energy. The colliding reactants
must possess a certain minimum amount of
energy for the collision to be effective
3. Collision orientation. Colliding reactants must
be oriented in a specific way if the reaction is
to occur.




We cannot measure absolute value for energy stored in a
chemical system. We can only measure the change in
energy (energy absorbed or released) as a chemical
reaction occurs.
System is the process understudy.
Surroundings encompasses the rest of the universe.
Energy is lost from the system to the surroundings or
energy energy may be gained by the system at the
expense of the surroundings.
Exothermic and Endothermic
Chemical Reactions
Are used to classify chemical reactions.
 Exothermic chemical reaction is a chemical
reaction in which energy is released as the
reaction occurs.
-If the energy required to break the bonds is
less than the energy given off when the
bonds form, the reaction will release the
excess energy.
CH4+ 2O2
 CO2+ 2H2O + 211 kcal
Exothermic and Endothermic
Chemical Reactions

Endothermic chemical reaction is a chemical
reaction i which a continuous input of energy is
needed for the reaction to occur.
-If the energy required to break the bonds is
greater than the energy released when
bonds form, the reaction will need an
external supply of energy.
CH4+ 2O2 + 22 kcal

CO2+ 2H2O
KINETICS
Chemical kinetics is the study of the rate(or
speed) of chemical reaction.
-gives an indication of the mechanism of
a reaction
-a step-by-step description of how
reactants become products.
Factors that Affect Reaction Rate
Five major factors influence reaction rate:
• Structure of the reacting species,
• Concentration of reactants,
• Temperature of reactants,
• Physical state of reactants, and
• Presence of a catalyst.
1. Structure of the Reacting
Species
-Oppositely charged species often reacts
more rapidly than neutral species. (Ions with
the same charge do not react)
-The size and shape of reactant molecules
influence the rate of the reaction.
2. Concentration of Reactants
-the rate will generally increase as
concentration increases simply because a
higher concentration means more reactant
molecules in a given volume and therefore a
greater number of collision per unit time.
3. Temperature of Reactants
-the rate of a reaction increase as the
temperature increases, because the kinetic
energy of the reacting particles is directly
proportional to the kelvin temperature.
4. Physical State of Reactants
The rate of a reaction depends on the physical state of the reactants:
solid, liquid or gas.
-In solid state, the atoms, ions or compounds are restricted in
their motion.
-In gaseous state, the particles are free to move, but the spacing
between particles is so great that collision are relatively
infrequent.
-In liquid state the particles have both free motion, and proximity
to each other.
Hence reactions tend to be fastest in the liquid
state and slowest in the solid state.
5. The Presence of a Catalyst
-a catalyst is a substance that increases the
reaction rate. The catalyst interacts with the
reactants to create an alternative pathway
for the production of products.
Altering Equilibrium Conditions:
Disturbing an equilibrium has one of the
two results:
Either the forward reaction
speeds up (to produce more
products)
or the reverse reaction speeds up
(to produce addtional reactants).
If more products have been
produced, the equilibrium has
If more products have been
produced, the equilibrium has
Le Chatelier's Principle
• Introduced by Henri Louis Le Chatelier
• States that if a stress (change of conditions) is applied
to a system in equilibrium, the system readjust (change
of equilibrium position) in the direction that best
reduces the stress imposed on the system.
How will the gas-phase equilibrium be affected by
each of the following?
CH4(g) + 2H2S(g)+ Heat
a. The removal of H2(g)
CS2(g) + 4H2
How will the gas-phase equilibrium be affected by
each of the following?
CH4(g) + 2H2S(g)+ Heat
b. The addition of CS2(g)
CS2(g) + 4H2
How will the gas-phase equilibrium be affected by
each of the following?
CH4(g) + 2H2S(g)+ Heat
CS2(g) + 4H2
c. The increase in temperature
How will the gas-phase equilibrium be affected by
each of the following?
CH4(g) + 2H2S(g)+ Heat
d. A decrease in pressure
CS2(g) + 4H2
How will the gas-phase equilibrium be affected by
each of the following?
CH4(g) + 2H2S(g)+ Heat
d. A increase in pressure
CS2(g) + 4H2
How will the gas-phase equilibrium be affected by
each of the following?
CO(g) + 3H2(g)
CH4(g) + H2O(g) + heat
a. The removal of CH4(g)
How will the gas-phase equilibrium be affected by
each of the following?
CO(g) + 3H2(g)
CH4(g) + H2O(g) + heat
a. The addition of H20(g)
How will the gas-phase equilibrium be affected by
each of the following?
CO(g) + 3H2(g)
CH4(g) + H2O(g) + heat
a. A decrease in the temperature
How will the gas-phase equilibrium be affected by
each of the following?
CO(g) + 3H2(g)
CH4(g) + H2O(g) + heat
a. An increase in pressure
THE GENERALIZED EQUILIBRIUM-CONSTANT
EXPRESSION FOR A CHEMICAL REACTION
We write the general form of an equilibrium chemical reaction as
aA + bB  cC + dD
In which A and B represent reactants, C and D represent
products, and a,b,c, and d are the coefficients of the balanced
equation. The equilibrium constant expression for this
general case is
Keq= AC] [DB
c
d
a
b
Writing Equilibrium-Constant
Expressions
• An equilibrium-constant expression can be written only
after a correct, balanced chemical equation that
describes the equilibrium system has been developed.
• Each chemical reaction has a unique equilibrium
constant value at a specified temperature.
• The brackets represent molar concentration or molarity
• Only the concentration of gases and substances in
solution are shown, because their concentrations can
change.
INTERPRETING EQUILIBRIUM CONSTANTS
• The numerical value of the equilibrium constant tells us
the extent to which reactants have converted to
product.
The following generalization are useful:
• Keq greater than 1x102. A large numerical value of Keq
indicates that the numerator (product term) is much
larger than the denominator (reactant term) and that at
equilibrium mostly product is present.
• Keq less than 1x10-2. A large numerical value of Keq
indicates that the numerator (product term) is much
smaller than the denominator (reactant term) and that
at equilibrium mostly reactant is present.
• Keq between 1x10-2 and 1x102. In this case the
equilibrium mixture contains significant concentrations
of both reactants and products.
Question
• At a given temperature, the equilibrium constant for a
certain reaction is 1x1020. Does this equilibrium favor
products or reactants? Why?
• At a given temperature, the equilibrium constant for a
certain reaction is 1x10-18. Does this equilibrium favor
products or reactants? Why?
CALCULATING EQUILIBRIUM CONSTANTS
• The magnitude of the equilibrium constant for a
chemical reaction is determined experimentally.
Redox and Nonredox Chemical
Reactions

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Chemical reactions can also be classified in
terms of whether transfer of electrons occurs
Oxidation-reduction (redox) chemical reaction
is a chemical reaction in which there is a
transfer of electrons from one reactant to
another reactant.
Nonoxidation-reduction (nonredox) chemical
reaction is a chemical reaction in which there
is no transfer of electrons from one reactant to
another reactant.
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A “bookkeeping system” known as oxidation
numbers is used to identify whether electron
transfer occurs in a chemical reaction.
An oxidation number is a number that
represents the charge that an atom appears
to have when the electrons in each bond it is
participating in are assigned to the more
electronegative of the two atoms involved in
the bond.
Rules for determining oxidation
numbers

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1. The oxidation number of an element in its
elemental state is zero. Ex., The oxidation number of
Cu is zero, and the oxidation number of Cl2 is zero.
2. The oxidation number of a monatomic ion is
equal to the charge on the ion. Ex., Na+ ion has an
oxidation number of +1, and the S2- ion has an
oxidation number of -2.
3. The oxidation numbers of Groups IA and IIA
metals in compounds are always +1 and +2,
respectively.
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4. The oxidation number of hydrogen is +1 in most
hydrogen-containing compounds.
5. The oxidation number of of oxygen is -2 in most
oxygen-containing compounds.
6. In binary molecular compounds, the more
electronegative element is assigned a negative
oxidation number equal to its charge in binary
ionic compounds. Ex., in CCl4 the element Cl is the
more electronegative, and its oxidation number is
-1.
7. For a compound, the sum of the individual
oxidation numbers is equal to zero; for a
polyatomic ion, the sum is equal to the charge on
Assigning Oxidation Numbers

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
Assign an oxidation number to each element
in the following compounds or polyatomic ions.
1. P2O5
2. KMnO4
3. NO3-
Redox and Nonredox Chemical
Reactions



Chemical reactions can also be classified in
terms of whether transfer of electrons occurs
Oxidation-reduction (redox) chemical reaction
is a chemical reaction in which there is a
transfer of electrons from one reactant to
another reactant.
Nonoxidation-reduction (nonredox) chemical
reaction is a chemical reaction in which there
is no transfer of electrons from one reactant to
another reactant.
Redox and Nonredox Chemical
Reactions



Determine whether the following reaction is a
redox reaction or a nonredox reaction.
Ca + Cl2 --> CaCl2
CaCO3 --> CaO + CO2
Ca + Cl2 -->
0
0
CaCl
+2 2-1

Redox reaction. Changes in
the oxidation number are a
requirement for a redox reaction.
CaCO3 --> CaO +
+2 +4 -2
+2 -2
CO
+42-2
Nonredox reaction. There are

no changes in the oxidation
number.
Using Oxidation Numbers to determine whether a
chemical reaction is a redox reaction or a
nonredox reaction.


4NH3 + 3O2 ---->
SO3 + H2O ---->
H2SO4
2N2
+ 6H2O
Reactant
Terminology associated with Redox
Process
Term
Electron Transfer
Oxidation
Loss of electron(s)
Reduction
Gain of electron(s)
Oxidizing agent
(substance reduced)
electron(s) gained
Reducing agent
(substance oxidized)
electron(s) lost
Leads to an inc. Of
oxidation number
Leads to an decrease
of oxidation number
Identifying the oxidation agent and
reducing agent in a Redox Reaction

For the redox reaction

FeO + CO
+2

-2
+2 -2
+4 -2
----> Fe + CO2
Identify the following:




a. The substance oxidized
b. The substance reduced
c. The oxidizing agent
d. The reducing agent
CO
FeO
FeO
CO
0
For the redox reaction
 3MnO
4Al ---->
2 +
3Mn

2Al2O3 +
Identify the following.
 a. The substance oxidized
 b. The substance reduce

c. The oxidizing agent
 d. The reducing agent
