ACTIVITY 5
Endothermic AND Exothermic Reactions
GROUP 2
INTRODUCTION
Whenever Physical changes and Chemical
changes occur in matter, energy changes are
also accompanied, which is mainly heat energy.
Two kinds of thermal reactions are Endothermic
reaction and Exothermic reaction.
 Endothermic Reaction – Reaction that
absorbs heat.
 Exothermic Reaction – Reaction that releases
heat.
LAW OF CONSERVATION OF ENERGY
Energy cannot be destroyed nor created
Endothermic process

Heat flows into the system from the
surroundings in an endothermic process.
Surroundings
Cold
pack
Energy
Temperature falls
4
Energy Level Diagrams
Endothermic reactions
products
energy
reactants
The products are
higher in energy
than the reactants
energy taken in
is positive
time of reaction
5
The products are higher in energy
than the reactants.
In this case making the bonds gives you
less energy than breaking them.
6
Exothermic process

Heat flows into the surroundings from the
system in an exothermic process.
Surroundings
Energy
Hot pack
Temperature rises
7
Energy Level Diagrams
Exothermic reactions
energyreactants
Energy given out
is negative
products
Time
of
reaction
The products are lower in
energy than the reactants
8
The products are lower in energy than the
reactants.
In this case making the bonds gives you
more energy than breaking them.
9
 Objective
To determine the energy changes that occur
during the reaction of Citric Acid and Baking
Soda and also the reaction of Hydrochloric
Acid and Magnesium Ribbon.
Apparatus:
 Beam Balance
 Beaker, 250 mL
 Graduated Cylinder
 Spatula
 Watch Glass
 Thermometer
Materials: (Chemicals)
 Baking Soda
 1.5 M Citric Acid
 2M HCl
 Magnesium Ribbon
Data and Results:
Citric Acid + Baking
Soda
HCl + Mg Ribbon
Final Temp.
22 ºc
34 ºc
Initial Temp.
28 ºc
27 ºc
Temp. Change
-6 ºc
7 ºc
(1)H₃C₆H₅O ₇ (aq) + 3NaHCO₃ (s) 3 CO₂ (g) + 3H₂O (l) + Na₃C₆H₅O₇
(2)Mg(s) + 2HCl (aq) H₂ (g) + MgCl₂ (aq)
Q’s & A’s :
 1. What type of energy change is associated
with the chemical reaction?
Citric Acid + Baking Soda : Endothermic Reaction
Mg + HCl : Exothermic Reaction
 2. How do the experimental data support the
energy changes describe?
A: Due to the differences of FINAL and INITIAL
temperature. The higher the differences in
temperature, the higher the changes in energy.
 3. What does a negative change in
temperature value indicates?
A: It indicates that the temperature decreases. Meaning
an Endothermic reaction is taking place or heat is
required to perform chemical reaction.
 4.Describe 3 ways to determine the chemical
reaction has taken place?
1.
2.
3.
Changes in temperature.
New substance(s) is formed
Changes in color
 5. Which reaction took place at a greater rate?
Explain.
A: HCl + Mg ribbon. This is because the differences in
temperature is greater than the differences of
temperature of the Citric Acid+ Baking Soda.
Conclusion:
 Whenever chemical reactions take place, it is
always accompanied by changes in energy,
especially heat energy.
Done by:
 Pineda, Aaron Russell
 Ong, Mika
 D’souza, Antonella
 Kang, Tai Woo
 Jo, Bean