1. Endothermic and
Exothermic
Reactions

3. Physical Change
• change in size, shape, color, or state of
matter

4. Chemical Reactions
• process in which one or more substances
are changed into others. Chemical
reactions are accompanied by a loss or
gain of energy.
• Indicators of chemical changes are
evident.
Indicators:
•Temperature change
•Odor change
•Formation of a precipitate
And sometimes…
•Color change

5. Activation Energy
•the smallest amount of
energy needed to make a
substance react

6. Exothermic
• energy (heat, light, electrical, etc.) is
given off; surroundings usually feel
warmer
- ex. Combustion, evaporation of
water

7. Cellular Respiration
Cellular respiration allows organisms to use
(release) energy stored in the chemical bonds of
glucose (C6H12O6). The energy in glucose is used to
produce ATP. Cells use ATP to supply their energy
needs. Cellular respiration is therefore a process in
which the energy in glucose is transferred to ATP.
This is an example of an exothermic reaction.

8. Exothermic Diagram
Energy
level
Activation
energy
Reactants
Using a catalyst
might lower the
activation energy
Energy given
out by
reaction
Products
Reaction progress
© Teachable . Some rights reserved. http://teachable.net/res.asp?r=1910

9. 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

10. Endothermic
• A chemical reaction in which energy is
absorbed; surroundings usually feel cooler
- ex. Cold packs, melting ice

11. Endothermic Diagram
Energy
Activation
energy
Products
Energy
absorbed by
reaction
Reactants
Reaction progress
© Teachable . Some rights reserved. http://teachable.net/res.asp?r=1910

12. 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.

13. Photosynthesis
During photosynthesis, plants absorb the
energy from the sun to convert carbon
dioxide and water into glucose and oxygen.
This is an example of an endothermic
reaction.
sunlight + 6CO2 + 6H2O  C6H12O6 + 6O2

14. True or False
Chemical reactions always produce heat
F

15. Chemical reactions can release or
absorb heat, but can also create
light, sound, or electricity!

16. True or False
Heat can be lost, destroyed
or just disappear
F

17. 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

18. True or False
Color change is always a physical property
F

19. Color is a physical
property.
Color change can be the result
of a chemical change.

20. Set up your Lab
Notebook like this:
________________ Experiment
(You’ll fill in the blank after the
experiment.)
Citric acid solution temperature: _____
Citric acid + NaHCO3 temperature:___
Reaction time: ___________________

21. Experiment
Procedures:
1.Pour 25 mL citric acid solution in
a Styrofoam cup. Use a
thermometer or other temperature
probe to record the initial
temperature.

22. Experiment
2. Stir in 15g baking soda (sodium
bicarbonate). Track the change in
temperature as a function of time.
This means you will start a timer when
you add the baking soda. Stop the
timer when the temperature no longer
changes.

23. Explain
1. Describe what happens when
baking soda and citric acid are
mixed.
2. What are evidences of chemical
change?

24. Explain
3. Is this an endothermic or
exothermic reaction?
How do you know?

25. Set up your Lab
Notebook like this:
___________ Experiment (You’ll fill
in the blank after the experiment.)
Jar temperature: _____
Temperature of steel wool soaked
in vinegar: ________

26. Experiment
Procedures:
1. Place the thermometer in the jar
and close the lid. Allow about 5
minutes for the thermometer to
record the temperature, then open
the lid and remove the
thermometer. Take a reading.

27. Experiment
2. Soak a piece of steel wool
in vinegar for 1 minute.
3. Squeeze the excess
vinegar out of the steel wool.

28. Experiment
4. Wrap the wool around the
thermometer and place the
wool/thermometer in the jar, sealing
the lid.
5. Allow 5 minutes, then read the
temperature and compare it with
the first reading.

29. Explain
Is this an endothermic
or exothermic reaction?
How do you know?

30. Clean-Up
Experiment 1:
Pour citric acid and baking
soda solution into the sink
while running water.
Rinse the cup. Place it back
at your station for the next
class.
Replenish any materials
necessary for next period.
Experiment 2:
Place steel wool in the trash.
Wipe out jar with paper
towel.
Replace thermometer in jar
and close the lid.
Replenish any materials
necessary for next period.