Science Module
th
8
Grade
TAKS Objective 3 – The student will
demonstrate an understanding of the
structures and properties of matter.
• Complex interactions occur between
matter and energy.
TEKS 8.10 (C)
The student knows that complex interactions
occur between matter and energy. The
student is expected to:
identify and demonstrate that loss or
gain of heat energy occurs during
exothermic and endothermic chemical
reactions.
Learning Objectives
1. identify endothermic and exothermic
reactions associated with chemical
changes
2. Explain the loss or gain of heat during
chemical reactions
3. Identify chemical and physical changes
associated with endothermic and
exothermic reactions
Background
Heat- transfer of energy
Exothermic- heat energy EXITS the system
- ex. Combustion, evaporation of water
- surroundings usually feel warmer
Salt
An example of an exothermic
reaction is the mixture of sodium
metal and chlorine gas which
yields table salt.
2Na(s) + Cl2(g)  2NaCl(s) + energy
Endothermic- heat energy ENTERS the system
- ex. Cold packs, melting ice
- surroundings usually feel cooler
How do cold packs work?
The outer pouch contains water. The inner pouch
contains ammonium-nitrate.
When you “pop” the inner pouch, the chemical
reaction absorbs heat energy from the
surroundings. This is an endothermic reaction.
The temperature of the solution falls to about 35 F
for 10 to 15 minutes.
Photosynthesis
During photosynthesis, plants absorb the
energy from the sun to convert carbon
dioxide and water into glucose and oxygen.
sunlight + 6CO2(g) + 6H2O(l)  C6H12O6(aq) + 6O2(g)
Physical change- change in size, shape or
state of matter
Chemical Reaction - process in which one
or more substances are changed into
others. Chemical reactions are
accompanied by a loss or gain of energy.
True or False
Chemical reactions always produce heat
Chemical reactions can release or
absorb heat, but can also create
light, sound or electricity!
True or False
Heat can be lost, destroyed
or just disappear
Heat energy is transferred from one object
to another, or is transferred to another
form of energy, but never disappears.
Law of Conservation of Energy
True or False
Color change is always a physical property
Color is a physical property.
Color change can be the result
of a chemical change.
ENGAGE
• Cold Packs
• Rubber Bands
• Glo-sticks
EXPLORE
• Hot or Not
– students explore endothermic and
exothermic chemical reactions using baking
soda and calcium chloride
EXPLAIN
1. List 3 physical properties of matter.
2. List 3 physical properties for:
•
•
•
Calcium chloride
Baking soda
Phenol red solution
3. Describe what happens with baking soda
and calcium chloride are mixed.
4. Describe what happens with baking
soda, calcium chloride and phenol red
are mixed.
5. What are evidences of chemical change?
6. Is this an endothermic or exothermic
reaction? How do you know?
7. Give three examples of exothermic
reactions in everyday life.
ELABORATE
• Ice Ice Baby
– Baking soda and vinegar
– Is this endothermic or exothermic? How do
you know?
– Give 3 examples of everyday endothermic
reactions.
• Ice Cream
– Are the changes physical or chemical?
– Is the ice cream endothermic or exothermic?
How do you know?
– Is the ice/salt mix endothermic or exothermic?
How do you know?
EVALUATION
• Complete Type of Change? Endo/Exo
chart
• Complete graph analysis questions