Demonstrate a simple chemical change to an elementary class by making hot chocolate in the classroom. Make the hot chocolate in front of the class, explaining the process of combining differing chemicals, such as water in liquid form and coco in solid form. Explain that the change uses heat to force the ingredients to become a single liquid. Give the students marshmallows or chocolate chips to put in their own cups of hot chocolate. Instruct the students to mix the extra ingredients in their cups and to watch as those extras use the heat from the liquid to melt and combine with the other ingredients.
While it is a commonly known fact that water freezes at 32˚ F, you can show students how additives in water can change this fact. Give each group of students a glass beaker, half filled with purified water. Instruct the students to place four teaspoons of salt in each beaker and to stir it until the salt is no longer visible. Instruct them to add ice to each beaker, along with a thermometer. Have the students watch as the temperature of the water lowers to freezing and below. As the ice melts, instruct them to add more ice to their beaker. Once the temperature is below 32˚ F, explain that it is the salt acting as an impurity in the water that keeps it from forming solid ice. Explain that the addition of salt represents a chemical change, meaning they are no long trying to freeze water, but trying to freeze salt water.
Many chemical reactions are too dangerous to watch in an elementary-school classroom, but a baking-soda and vinegar reaction is safe and can demonstrate how a solid and a liquid combine to form a gas. Instruct the students to gather while you demonstrate this experiment. Place two teaspoons of baking soda in a beaker. Pour two ounces of vinegar into the beaker: pour slowly to avoid an excessive mess. As the mixture bubbles and foams, explain that the chemicals are changing before their eyes, and reacting violently to the change.
Reproduce popular experiments students may have seen on TV or YouTube, but explain the science behind the experiments. Escort the class outdoors and bring a two-liter bottle of Diet Coke, a package of chewable Mentos, a test tube and an index card. Open the bottle of Coke and place the index card over the mouth of the bottle. Place the package of Mentos in the test tube, turn it upside down and place it against the index card, directly over the mouth of the soda. Slide the index card out, wait for the Mentos to drop into the soda, and run. Explain how tiny holes in the Mentos candy increase the available surface area of the candy, while the surface contact with the Diet Coke creates the reaction, releasing carbon dioxide at a very rapid pace. While messy, this fun experiment is another example of the high volatility of chemical changes.