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Crazy About Reactions
Teacher’s Instructions
Teaching Objectives:
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Students will learn about chemical reactions.
Students will conduct their own endothermic and exothermic reactions.
Students will observe the effects of temperature on density.
Recommended Grades: 4-8
Estimated Time: 50 minutes
Prep Time: 10-15 minutes
Clean-up Time: 10-15 minutes
Key Terms:
Chemical reaction- a chemical change that forms a new substance
Exothermic reaction- Heat is released when a reaction takes place
Endothermic reaction- Heat is absorbed when a reactions takes place
Catalyst- Helps increase the speed of a reaction but does not undergo a chemical reaction
Density- mass per unit of volume
Procedure:
1. Pair up the students. Each pair will conduct both reactions. In front of each pair,
place 1 paper cup, 2 plastic cups, 1 plastic bin, thermometer, measuring cups, room
temperature water, bottle of hydrogen peroxide, and a bag of Epsom salt and yeast.
If the students are grades 5-8 allow them to measure every ingredient on their own..
If the students are grades K-4, pre-measure all ingredients. Make sure to label all
plastic bags or containers so the students know what everything is. By premeasuring the ingredients, you will minimize some of the mess.
2. Before the class starts, heat up water and use ice to cool water. It will later be used
in the density demonstration.
3. Give the class examples of chemical reactions and ask them to come up with some of
their own.
Kimi Kossler
January 2012
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4. Start with the endothermic reaction. Ask the students predict what will happen to
the temperature of the water when Epsom salt is added to it. Then let them carry
out the experiment. Remind them to record all of the data and their observations on
worksheet 1.
5. Next, have the students perform the exothermic reaction. Ask the students predict
what will happen to the temperature of the hydrogen peroxide when yeast is added
to it.
6. Introduce the density demonstration by asking the class what the definition of
density is. Ask them if they think it will be possible to keep the two colors of water
separated when the bottles are placed on top of each other.
7. Make sure to conduct this demonstration in a plastic bin because some of the blue
water might spill. Make sure the water is not too hot because the blue water is hot
and tends to spill. This demonstration will require two people.
8. After the demonstration ask the students why the colors did not mix. Tell them
about the effects of temperature on the density of water.
How it works:
Endothermic Reaction
An endothermic reaction is a chemical reaction that requires heat in order to occur. This
means that heat is absorbed from the surrounding areas. For this experiment, the Epsom
salt is absorbing the heat from the water, thus causing the temperature of the water to
decrease.
Examples:
Melting ice cubes
Melting salts
Evaporating water
Photosynthesis
Cooking an egg
Baking bread, cake, etc
Exothermic Reaction
An exothermic reaction is a chemical reaction that releases heat. For this experiment, the
hydrogen peroxide undergoes a decomposition reaction. This means that the hydrogen
peroxide breaks down into different components, oxygen gas (bubbles) and water. Heat is
also a product of the decomposition reaction. The yeast acts as a catalyst, which means that
it helps increase the rate of the decomposition (breakdown) of the hydrogen peroxide, but
itself does not undergo any chemical change.
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January 2012
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Examples:
Process of making table salt (NaCl)
Making ice cubes
Burning a candle
Mixing water and strong acids
Rusting iron
Formation of snow in clouds
Burning wood
Temperature and Density
Cold liquids are denser than hot liquids. In cold liquids, the molecules move around less
because they have less energy to move around. This means that the molecules are packed
closer together. Another way to look at it is that more molecules in a cold liquid are able to
pack in the same total volume than the molecules in a hot liquid. Hot liquids are less dense
so it will float on top of the cold water instead of mixing with the cold water. The colored
water will eventually mix together once they both reach the same temperature.
References:
Bardhan-Quallen, Sudipta. Championship Science Fair Projects: 100 Sure-to-Win
Experiments. Scholastic Inc: New York. 2005.
Water Density Experiment. http://raisingsparks.com/kids-science/water-densityexperiment/. (accessed January 9, 2012).
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January 2012
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Crazy About Reactions
Materials List
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Hydrogen peroxide: ¼ cup per pair
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Thermometers: 1 per pair
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Measuring cups
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Paper cups: 1 per pair
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Plastic cups: 3 per pair
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Medium size plastic bins: 1 per pair
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Yeast: 1 tablespoon per pair
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Epsom salt: 1 tablespoon per pair
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Water
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Device to heat water (microwave, hot plate, electric kettle)
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Ice to cool water
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Empty soda bottles 16.9 fl oz: 2 per pair
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Food coloring
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Index cards: 1 per pair
Kimi Kossler
January 2012
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Crazy About Reactions
Student’s Instructions
You have entered into a science competition. There are three criteria: you have to make a
liquid colder, make a liquid hotter, and prevent two different colors of water from mixing
when put together. Are you up for the challenge?
You will need:
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Hydrogen peroxide
Yeast
Epsom salt
Food coloring
Thermometer
Plastic cups
Paper cup
Hot water
Cold water
Room temperature water
Plastic soda bottles 16.9 fl oz
Index card
Plastic bin
Procedure:
Part A- Endothermic Reaction
1. Place the paper cup inside of the plastic bin. Fill the paper cup half way with room
temperature water. Using the thermometer measure the temperature of the water.
2. Measure 1 tablespoon of Epsom salt and add it to the paper cup. Mix the liquid until
the salt has dissolved.
3. Record the temperature with the thermometer every two minutes for a total of ten
minutes.
4. Dump out the liquid in the paper cup into the sink.
5. Repeat steps 1-3, but add 2 tablespoons of Epsom salt to the water instead.
6. Record the temperature with the thermometer every two minutes for a total of ten
minutes.
7. Write down all observations on your worksheet.
Part B- Exothermic Reaction
1. Place the plastic cup inside of the plastic bin.
2. Measure ¼ cup of hydrogen peroxide and pour it into the plastic cup. Using the
thermometer measure the temperature of the hydrogen peroxide.
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January 2012
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3. Measure 1 tablespoon of yeast and add it to the plastic cup.
4. Record the temperature with the thermometer every two minutes for a total of ten
minutes.
5. Repeat steps 1-3, but add 2 tablespoons of yeast to the hydrogen peroxide instead.
6. Record the temperature with the thermometer every two minutes for a total of ten
minutes.
7. Write down all observations on your worksheet.
Part C- Temperature and Density (Demo)
1. Fill one soda bottle with cold water. Add red food coloring to the cold water.
2. Fill the other bottle with hot water (not boiling). Add blue food coloring to the hot
water.
3. Before inverting the bottle place everything in a plastic bin because the blue water
will spill. Using an index card, invert the blue soda bottle. Line up the openings with
the red soda bottle. Once it is aligned, carefully remove the index card.
4. Record your observations on the worksheet.
Kimi Kossler
January 2012
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Name: _________________________________________
Date: __________________________________________
Crazy About Reactions
Worksheet 1
Endothermic reaction #1
Time
Temperature
Outside of paper cup
0 minutes (before Epsom
salt is added)
2 minutes
4 minutes
6 minutes
8 minutes
10 minutes
Endothermic reaction #2
Time
Temperature
Outside of paper cup
0 minutes (before Epsom
salt is added)
2 minutes
4 minutes
6 minutes
8 minutes
10 minutes
Kimi Kossler
January 2012
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Exothermic reaction #1
Time
Temperature
Outside of paper cup
Temperature
Outside of paper cup
0 minutes (before yeast is
added)
2 minutes
4 minutes
6 minutes
8 minutes
10 minutes
Exothermic reaction #2
Time
0 minutes (before yeast is
added)
2 minutes
4 minutes
6 minutes
8 minutes
10 minutes
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January 2012
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Name: _________________________________________
Date: __________________________________________
Temperature and Density Demo
Color
Location (circle the answer)
Top or bottom
Top or bottom
Kimi Kossler
January 2012
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Name: _________________________________________
Date: __________________________________________
Crazy About Reactions
Worksheet 2
Define terms:
Endothermic reaction-
Exothermic reaction-
Catalyst-
Questions:
1. What was added to the water to cause the temperature of the water to decrease?
2. What was added to the hydrogen peroxide to cause the temperature of the hydrogen
peroxide to increase?
3. What was the catalyst in the exothermic reaction?
4. Did adding 2 tablespoons of Epsom salt and yeast cause the temperature to change
more than when only 1 tablespoon was added?
Kimi Kossler
January 2012
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Name: _________________________________________
Date: __________________________________________
5. Why did the blue and red water not mix?
6. Is hot water more dense or less dense than cold water? Why?
Kimi Kossler
January 2012