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Chemical
Energy
Summary: This activity shows chemical energy being
converted to heat energy.
Introduction:
Chemical energy is the
energy stored in molecules (made up of atoms---the building blocks
of matter). Molecules of food and fuels, for example, store the
chemical energy that can be released in certain chemcial reactions.
In this activity, you will mix two chemicals--sodium carbonate
and water--together. When these two chemicals are mixed together,
the mixture gets warm becasue it releases the heat energy. Using
a temperature probe you will measure the change in heat energy.
Materials:
- washing soda (Arm & Hammer
available at local grocery store)
- 250 - 500 ml measuring cup (8
- 16 oz)
- water (1000 ml or 32 oz per group)
- several clear plastic cups or
beakers per group (250 ml or 8 oz)
- temperature probe
- measuring spoons
- stirring spoon or rod
- large container for waste solutions
- goggles
Safety Concerns:
- Warning: This compound is very
alkaline and can damage skin and eyes. Do not rub into eyes and
wash your hands immediately after completing the activity.
- Wear safety goggles and wash hands
thoroughly when finished.
Classroom Management:
Before starting the activity,
have each student group collaborate on the design of several
procedures that vary the amount of washing soda added to the
water. Have them test their procedures.
Activity Steps:
1. Design the experiment.
- Using at least three plastic cups,
design and record a procedure to vary the amount of washing soda
you will add to the same amount of water. For example, 1 tablespoon
(5 ml) in 100 ml of water, 2 tablespoons (10 ml) in 100 ml of
water, etc. Remember, when ever you design an experiment it should
be controlled. If you change the amount of washning soda,
the amount of water should remain the same.
- Predict which quantity of washing
soda will get the warmest?
2. Will different amounts of
washing soda added to the water produce a different amount of
heat energy?
- Record the temperature of the
water in each cup with the temperature probe before you add the
washing soda.
- Continue recording the change
in temperature as the washing soda is added and dissolved (by
stirring) into solution.
- Did different amounts of washing
soda produce more heat?
3. Make a general statement
about how chemcial energy can be converted to another form.
Extensions:
The mixing of washing soda and
water is used to make a "hot pack" for athletic injuries.
Not all chemicals give off "heat" to their surroundings
when mixed. Some chemicals take "heat" from their surroundings.
"Cold packs" are examples of chemicals that take "heat"
from their surroundings. Make and test your own "cold pack"
with ammonium nitrate and water.
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