Exothermic Reactions

Learning Outcomes

A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another.  Chemical reactions are an integral part of technology, of culture, and indeed of life itself.  An exothermic reaction is a chemical reaction that releases energy by light or heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation: reactants → products + energy. This exercise will allow you to understand chemical reactions, explain what happens during an endothermic reaction, explain the role of a catalyst and make both quantitative and qualitative scientific observations.

Materials

• A clean 16-ounce plastic soda bottle or large cup
• 1/4 cup 20-volume hydrogen peroxide liquid (20-volume is a 6% solution, ask an adult to get this from a beauty supply store or hair salon, can also be purchased on Amazon)
• 1/2 Tablespoon (one packet) of dry yeast
• 1 1/2 Tablespoons of warm water
• 1 tbsp Liquid dish washing soap
• Food coloring (optional)
• Small bathroom cup (approx. 2 oz) cup
• Safety goggles and gloves
• High temperature thermometer (we use Vernier LabQuest 2 eith temperature sensor)

How It Works

Caution: Hydrogen peroxide can irritate skin and eyes.  Wear goggles and gloves.

1. Carefully pour the hydrogen peroxide into the bottle or large cup. Take the temperature of the hydrogen peroxide and record the initial temperature in the data table below.
2. Add 8 drops of your favorite food coloring into the bottle.
3. Add about 1 tablespoon of liquid dish soap into the bottle and gently swish the bottle around a bit to mix it. You do not want bubbles to form.
4. In a separate small cup, combine the warm water and the yeast together and mix for about 30 seconds.
5. Now the adventure starts! Pour the yeast water mixture into the bottle (a funnel helps here) and watch the foaminess begin!
6. 6. Track the change in temperature as a function of time. Record the first meeting as 1 min, then continue recording the temperature in minute increments over 5 minutes.

7. Make observations.

How does it work?

The foam you made is special because each tiny foam bubble is filled with oxygen. The yeast acted as a catalyst (a helper) to remove the oxygen from the hydrogen peroxide. Since it did this very fast, it created lots and lots of bubbles

8. Clean up. The foam produced is just water, soap, and oxygen so you can clean it up with a sponge and pour any extra liquid left in the bottle down the drain.

Additional Resources

• Chemical Reaction Lesson Plan