Lesson 5: Chemical Energy


Activity 1: Modeling Molecules

Materials: large marshmallows, periodic table of elements (kit), small, colored marshmallows, uncooked spaghetti noodles
Each element on the periodic table of elements has its own symbol. The symbol for hydrogen is H. Find hydrogen on your periodic table. Try a few more to get familiar with the periodic table:
  • What element has the symbol of Ti?
  • What is the symbol for helium?
  • What is the element Sn?
Remember that a molecule is two or more atoms bonded together. These atoms can be the same element, or they can be different elements. When we want to describe what a molecule is made of, we use the symbols of each atom and put them together into a chemical formula. Here is an example of a formula you are very familiar with:
This, of course, is the chemical formula for water. Chemical formulas tell you the names of the elements in the molecules and how many atoms of each element there are. The formula for water indicates that there are two hydrogen atoms and one oxygen atom in a molecule of water. As you saw in today's reading, this is what a water molecule looks like:
On the "Modeling Molecules" activity page you will find a list of some common molecules. Using your periodic table of elements 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 other atoms. You may also want to use the small marshmallows to represent oxygen in the copper sulfate molecule.

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
First, your child should have used the periodic table to find out the following:
  • What element has the symbol of Ti? (titanium)
  • What is the symbol for helium? (He)
  • What is the element Sn? (tin)
Your child will use marshmallows and spaghetti to model some common molecules. 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. (The answer key shows each atom labeled for your reference. Your child's models do not need to be labeled unless he wants to do so.)

Activity 2: Matter and Energy

Materials: colored pencils or markers, scissors
In the last lesson you learned about the laws of thermodynamics. Remember that the first law of thermodynamics says that neither energy nor matter can be created or destroyed, but they can change. Matter can change from one state — from being a solid, liquid, or a gas — to another state. Melting ice is an example of matter (water) changing from a solid to a liquid. Elements can be combined to form new substances, as you modeled in Activity 1. Energy can change from chemical to electric to kinetic, or from light to heat. You have already conducted experiments in the last few lessons to observe how energy can be changed from one form to another.

Scientists have another name for the first law of thermodynamics: the law of conservation of mass-energy. It tells us four important facts about matter and energy:
  1. Matter can't be created or destroyed.
  2. Energy can't be created or destroyed.
  3. Sometimes energy can be changed into matter.
  4. Sometimes matter can be changed into energy.
This law says that the total amount of mass (matter) and energy in the entire universe remains the same, even if matter and energy change forms or change into each other.

Demonstrate these ideas by following the directions on the "Matter and Energy" activity page. When you have found words for each category, explain to a parent how your words demonstrate the law of conservation of mass-energy.
Student Activity Page
For this activity, your child will demonstrate his understanding of the law of conservation of mass-energy.

Answers will vary. Words for #3 and #4 will overlap, especially shorter words where half of the letters may come from each word. This is fine. The point of the activity is to reinforce the ideas that matter changes form, energy changes form, matter can change into energy, and energy can change into matter. Ask your child how the words he chose demonstrate those principles.

Some of the words your child may find include the following:
  1. rat, mat, team, tar, tram, mare, mart, meat, mate, rate, ream, are, tamer
  2. grey, green, eye, yen, rye
  3. enter, tree, many, germ, target, mean, name, yam, team
  4. grate, rage, range, ranger, year, eager, yearn, game, gamer, meager

Activity 3: Exothermic and Endothermic Reactions

Materials: baking soda, citric acid (kit), clear glass cup, glass jar (kit), graduated cylinder (kit), measuring spoons, plastic spoon, small bowl, steel wool (kit), thermometer (kit), vinegar
Chemical reactions cause atoms to rearrange into different combinations of matter, just as you demonstrated in Activity 2. It takes energy to begin a reaction because the bonds between atoms must be broken first. Energy is released when bonds are formed.

Review the difference between an exothermic and an endothermic reaction in your Let's Explore Energy booklet. Then conduct the two experiments on the "Exothermic and Endothermic Reactions" activity page.

Materials Note: Save the glass jar to use in Lesson 2 of "The Living Seas" unit.
Ask your child to explain what he observed during his endothermic and exothermic reactions.