This document discusses endothermic and exothermic reactions. It provides examples of exothermic reactions like combustion and cellular respiration which release energy. Exothermic reactions are illustrated as having energy released by the reactants. Endothermic reactions like photosynthesis and cold packs absorb energy, shown as energy being absorbed by the reactants. Both reaction types are accompanied by temperature changes or energy transfers that allow identification of whether energy is released or absorbed in a chemical reaction.

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

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. 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: ________

11. 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.

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

13. 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.

14. Explain
1. Is this an endothermic
or exothermic
reaction? How do you
know?
2. Fill in the blank in your
title.

15. Clean-Up
Experiment 1:
•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.

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

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

18. 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.

19. 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

20. True or False
Chemical reactions always produce heat
F

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

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

23. 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

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

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

26. Set up your Lab
Notebook like this:
________________ Experiment
(You’ll fill in the blank after the
experiment.)
Citric acid solution (H3C6H5O7)
temperature: _____
Citric acid + NaHCO3 temperature:___
Reaction time: ___________________

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

28. Experiment
2. Stir in 15g baking soda (sodium
bicarbonate: NaHCO3). 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.

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

30. Explain
3. Is this an endothermic
or exothermic reaction?
How do you know?
4. Fill in the blank in your
title.

31. Clean-Up
Experiment 2:
•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.