Usually on Wednesdays we feature Bug of the Week, so today’s chemistry lesson is inspired by insects.

Dr. Thomas Eisner was a very curious man. He was particularly curious about insects, like the beetle shown in this video (has pop-up ad).

When he discovered these particular beetles, Dr. Eisner began to experiment with them because he wanted to know what and how they were squirting. One of the unexpected things he found out was that the temperature of the spray the beetle released was very hot, nearly 100Â° C. How could that be?

Endothermic and Exothermic Reactions

Sometimes chemical reactions between two or more substances give off or take in energy, often in the form of heat. In exothermic reactions, heat energy is given off during the reaction and the temperature increases. In endothermic reactions heat energy is removed by the reaction (“taken in”) and the temperature of the reactants decreases.

Below are two chemical reactions that use household products. Find out whether they are exothermic or endothermic.

Notes:Â  These activities are messy fun, so perform them in a sink, tub, or outdoors in an area where wet spills are not a problem. Also, scientists never eat or drink their experiments!

# Reaction 1.

Materials:

• About 26 g lemonade drink mix* (make sure the primary ingredient is citric acid)
• Baking soda
• Liquid measuring cup
• 1/4 cup dry measuring cup
• Water (room temperature)
• Large Styrofoam cup (to help insulate the reaction)
• Container (glass or cup) to mix the drink mix and water in
• Thermometer or temperature probe
• Spoon

* Math alert:Â  Originally I used Crystal Light pink lemonade mix, which came in 3.68 g packets (see the serving size information for the number of grams per packet). I used 7 packets for about 28 g. Then I switched to an off brand, and the packets were 2.6 g each (10 packets for 26 g). It worked just as well. Also, check the amount of vitamin C information on the labels. The raspberry-flavored lemonade mix contained significantly more citric acid for some reason.

Procedure 1:

1. Measure 100 mL (approx. 1/3 cup) of room temperature water and pour into in a container.
2. Add 26 g of drink mix into the water in the container. Stir until completely dissolved.
3. Use the thermometer or probe to measure the temperature of the solution, taking care not to rest the thermometer or probe on the bottom or side of the cup.
4. Measure 1/4 cup baking soda into the Styrofoam cup.
5. In a sink or similar area, quickly add the drink mix solution to the baking soda in the Styrofoam cup.
6. As the reaction starts to slow, take the temperature again. (You may want to let the children touch the solution and compare to the room temperature water. They will need to wash their hands afterwards.)

Did the temperature of the contents of the Styrofoam cupÂ  go up or down?

# Reaction 2:

Materials:

• 2 teaspoons active yeast
• Liquid measuring cup
• Measuring teaspoon
• Water at room temperature
• Cup or similar container for mixing yeast
• Large Styrofoam cup
• Thermometer or temperature probe
• Hydrogen peroxide (be sure to use 3 %, the kind sold for home use) – held at room temperature
• Spoon

Procedure 2.

1. Measure 100 mL of room temperature water (approx. 1/3 cup) and pour into the yeast-mix container.
2. Mix the 2 teaspoons dry yeastÂ into the water. Stir until thoroughly mixed.
3. Take the temperature of the solution, taking care not to rest the thermometer on the bottom or side of the cup.
4. Add 100 mL (about 1/3 cup) 3% hydrogen peroxide to the Styrofoam cup.
5. Take the temperature of the hydrogen peroxide, taking care not to rest the thermometer on the bottom or side of the cup. The two solutions should be roughly the same temperature.
6. In a sink or similar area, add the yeast solution to the hydrogen peroxide in the Styrofoam cup.
7. As the reaction starts to slow, take the temperature again. (You may want to let the children touch the solution and compare to the room temperature water. They will need to wash their hands afterwards.)

Did the temperature go down or up?

Which reaction was endothermic? Which reaction was exothermic? Let us know what you find out.

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If you are interested in learning more about the beetles, read the first chapter in:

For Love of Insects by Thomas Eisner

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1. Bella

We did this in my homeroom, and the kids were in aw that exothermic and endothermic reaction could be that much fun! Huge help in my homeroom please do more exothermic and endothermic reactions.

Homeroom 174 🙂

2. Roberta

Thanks for letting me know. I’ll add a link here when I post more.

3. Josh

Baking soda and vinegar reaction is exothermic

4. susan john

interesting and exciting and very, very helpful for teachers and mothers- I should say! Thankyou!susan

5. hi

baking soad and vinegar are actualy endothermic

6. Roberta

Did you try it? What were your results?

Thanx for the help with my homework

8. Katie

What grade did you try this with? I teach middle school. Thanks.

9. Roberta

I’ve done it with a range of ages, including high school. Obviously the high school students were held to a higher level of understanding of the processes, with more experimentation, data collection, graphing, etc.

10. Cynthia

Can you share your results with us?

11. Roberta

Sorry, it has been a few days since I checked the comments. The acid plus baking soda is the endothermic reaction. Did you need more than that?

12. RW

Which one was Endothermic? We need an endothermic reaction and thought this was cool. Please let me know.

13. Roberta

I guess it won’t hurt to reveal it now. The baking soda and citric acid -Reaction 1– is the “cool” reaction. It is endothermic.

14. RW

Thank you so much!

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