Learning Outcomes
What I am Looking For is that you will be
able to…….:
Must (Grade F): State a definition for
exothermic and endothermic.
Should (Grade C/D): Recognize an exothermic
and endothermic reaction in a graph
Could (Grade B/A): Explain the difference
between endothermic and exothermic reactions.
Energy and Reactions

Energy is involved in chemical reactions in two
ways:
1.
to break some (or all) bonds between atoms in the
reactants so the atoms can form new bonds or
2.
when the atoms or products form new bonds to make
new products.
Two Types of Reactions
 We classify chemical reactions based on how the
energy of the reactants compares to the energy of
the products.
Exothermic reactions
 If forming new bonds
releases more energy than
it takes to break the old
bonds, the reaction is
exothermic.
Exothermic reactions
 A good example is the reaction of hydrogen
with oxygen.
Once started, exothermic reactions tend to keep
going as each reaction releases more energy to
fuel neighboring molecules.
Endothermic reactions
 If forming new bonds in
the products releases
less energy than it took
to break the original
bonds, the reaction is
endothermic.
Endothermic reactions
 An important endothermic reaction is
photosynthesis.
 Plants need energy from sunlight to make
glucose and oxygen from carbon dioxide and
water.
EXOTHERMIC
Chemical reactions
where HEAT…
Is transferred to the
surroundings…
Indicated by a RISE in
temperature
ENDOTHERMIC
Chemical reactions
where HEAT…
Is transferred from
the surroundings …
Indicated by a FALL
in temperature
Activation Energy
 Activation energy is the energy needed to begin a
reaction and break chemical bonds in the
reactants.
Activation Energy
 This is why a flammable
material like gasoline
does not burn without a
spark or flame.
Examples of
Endothermic Reactions
 Most of the reactions used in industry to produce
useful materials require more energy than they
produce.
 One process that uses endothermic reactions is the
refining of ores to produce useful metals.
Examples of
Endothermic Reactions
 Most of the reactions used in
industry to produce useful
materials require more energy
than they produce.
 The reaction taking place inside
an instant cold pack is
endothermic.
Examples of
Endothermic Reactions
 When you squeeze the plastic bag the water reacts
with the ammonium nitrate crystals, and the
reaction dissolves the ionic bonds in the ammonium
nitrate.
Examples of
Endothermic Reactions
ACTIVITY
Complete graph
Matching with
Partner.
Very
endothermic
reaction with
a big
activation
energy
Very
exothermic
reaction with
a small
activation
energy
.
Moderately
endothermic
reaction with
a
moderately
high
activation
energy.
also be seen
asusually
quite exothermic
a highly unlikely
Could
has a verywith
low activation
energy.zero activ
Exothermic without
Showing activation
energy
Moderately
exothermic
reaction with
a moderately
high
activation
energy
en as, probably impossible?).
Endothermic
Without activation
Energy being shown
Energy level diagram for an exothermic chemical reaction with
Energy level diagram for an exothermic chemical reaction
without showing the activation energy. It could also be seen
as quite zero activation energy, but reactions between two
ions of opposite charge usually has a very low activation
energy.
Energy is
equal. Possible
But not likely
Create a
SONG
POEM
DRAWING to explain
The difference between
Endothermic and
Exothermic reactions.
1. Explain the difference
Between endo and exo
Reactions.
2. Draw a graph of each
Type. Endo and exo
Label each
3. Write an equation for each
Words to be used
Endothermic
Exothermic
Activation energy
Absorbed
Released