Education:Science Projects: Hot and Cold
Experiment #1: Feel the Heat!
What you need
• a thermometer
• a bowl
• 1 tablespoon of quick-rising dry yeast (from the grocery store)
• 1/4 cup hydrogen peroxide (be careful with this—get an adult to help)
• a spoon
What you do
1. Look at the thermometer and see what temperature it is showing. Then put it in the bowl.
2. Pour the hydrogen peroxide in the bowl, add the yeast, and stir with the spoon.
3. Watch what happens, and feel the lower sides and bottom of the bowl.
4. Wait a minute or two, then spoon out the thermometer.
Now look at what temperature it is showing. Is there a difference? Why do you think these substances acted the way they did?
Why this happens
You've just seen an exothermic chemical reaction! When the yeast is mixed with the hydrogen peroxide, the molecules of the hydrogen peroxide change into oxygen and water. That change produces heat, and that's what exothermic means–a process that creates heat. The extra oxygen bubbles that were separated out escape in the form of bubbles.
Experiment #2: That's Cool
What you need
• a thermometer
• 1 tablespoon of Epsom salts (from the grocery or drug store). Be careful with this!
• tap water, neither hot nor cold
• a spoon
• a medium-sized jar
What you do
1. Fill the jar with tap water.
2. Place the thermometer in the water, and feel the temperature of the jar with your hands.
3. After a few minutes, take out the thermometer and read what temperature it is recording. Put it back in the jar.
4. Now stir in the Epsom salts with the spoon. Feel the jar again. Notice any difference?
5. After a couple of minutes, take out the thermometer and look at the temperature it is now showing. Any change? How come?
Why this happens
Now you've seen the opposite of an exothermic reaction—an endothermic reaction. In a chemical change, sometimes heat is used up instead of created, and that's endothermic. When you added the Epsom salts, which is magnesium sulfate, to the water, it used the water's heat energy to split apart the ions of sulfate and magnesium. Because it is using the heat, the water gets colder. Pretty cool!
