Lesson 5: Chemical Energy


Activity 1: Modeling Molecules

Materials: large marshmallows, periodic table of elements (kit), small, colored marshmallows, uncooked spaghetti noodles
Molecules are the building blocks of materials. They are made when two or more atoms are bonded chemically. Atoms are made of smaller particles called protons, electrons, and neutrons.
Diagram of an Atom
The periodic table is a list of all the elements on earth. An element is a substance made of one kind of atom. All matter is made of molecules that are a combination of one or more atoms of the elements on the table. A compound is a molecule made up of two or more elements from the table. For example, a water molecule is made up of two hydrogen atoms and one oxygen atom. This is a diagram of a water molecule:
Water Molecule
On the "Modeling Molecules" activity page you will find a list of some common molecules. Using a periodic table of elements (one is provided with this unit) as a reference, identify the elements that are joined together to form each molecule, and then create a model of the molecule using marshmallows and spaghetti. Use small marshmallows to represent hydrogen, and use large marshmallows to represent the other atoms. Hydrogen atoms are smaller than the other atoms.

On your first try you will probably not structure the atoms just right. That is okay. Give it your best guess, and then you can correct the marshmallow structures with your parent after you have given it one try.
Student Activity Page
Check your child's molecules to see that they reflect the correct atoms and number of atoms. The structure will likely be different for some of the molecules. This is okay. After he has worked through the molecules once on his own, you can go back with him and model the elements as they actually exist.
"Modeling Molecules" Answer Key

Activity 2: Chemical Changes

Materials: ScienceWiz Energy box, baking soda, clear glass cup, vinegar
Remember that neither energy nor matter can be created or destroyed, but they can change. Matter can change from a solid, liquid, or a gas state. Energy can change from chemical to electric to kinetic, and from light to heat. You have already conducted experiments in your ScienceWiz Energy box to observe how energy can be changed.

Now you can observe a chemical reaction that creates a new compound by conducting the investigation on page 18 of the book in your ScienceWiz Energy box. The new compound is a gas, even though the first two compounds are a solid and a liquid.
For this activity, your child will observe a chemical reaction. Ask him to describe what occurred during the reaction.

Activity 3: Exothermic and Endothermic Reactions

Materials: baking soda, citric acid (kit), clear glass cup, graduated cylinder (kit), jar with lid (kit), measuring spoons, plastic spoon, steel wool (kit), thermometer (kit), vinegar
Chemical reactions cause bonds between atoms to break or change and result in something new. A new compound may be produced and energy may be produced.

When a chemical reaction occurs, we have reactants and products. Reactants are the substances that are combined, and the products are the substances that exist after the change has taken place.

There are two kinds of chemical reactions. An exothermic reaction is a chemical reaction that releases heat. In an endothermic reaction, heat energy is taken in and is transformed into chemical bond energy. Conduct the exothermic reaction described on the "Exothermic Reaction/Endothermic Reaction" activity page.

Exothermic Reaction
Reactants —> Products + Energy

Endothermic Reaction
Reactants + Plus Energy —> Products

The products that occur from an endothermic reaction are cooler than the reactants. The products that occur from an exothermic reaction are warmer.

Remember that energy cannot be created or destroyed, only changed from one kind to another. The heat produced from an exothermic chemical reaction is not created but comes from the stored energy in the combined reactants. As you learned in the energy experiments in the ScienceWiz Energy box, chemical energy can be converted to different types of energy, including heat, light, and electrical energy. Conduct the endothermic reaction on the activity sheet.

Materials Note
If you have trouble locating citric acid, you can try this experiment with lemon juice instead.
Ask your child to explain what he observed during his endothermic and exothermic reactions.