CHEMICAL REACTONS Key Concepts:
A physical change, such as a state change or dissolving, does not create a new substance, but
a chemical change does.
• In a chemical reaction, the atoms and molecules that interact with each other are called
reactants.
• In a chemical reaction, the atoms and molecules produced by the reaction are called
products.
• In a chemical reaction, only the atoms present in the reactants can end up in the products.
No new atoms are created, and no atoms are destroyed.
• In a chemical reaction, reactants contact each other, bonds between atoms in the reactants
are broken, and atoms rearrange and form new bonds to make the products.
Matter is never destroyed or created in chemical reactions. The particles of one substance are
rearranged to form a new substance. The same number of particles that exist before the reaction
exist after the reaction.
Evidence of a chemical reaction
Gas is Produced
Mini labs:
Canister with lid add vinegar then baking soda and close lid, the gas pushes the top off.
Water bottle and balloon: vinegar in bottle, baking soda in balloon, hold up balloon and see
gas (CO2) fill up balloon.
In petri dish, place some turmeric?? And washing soda, wait a few seconds and watch it
bubble.
Light is Produced
An example of this is a glow in the dark necklace (break one and let the liquid leak into a
beaker, then add water and the glow appears) project black light for a more intense look.
a Change in Color: remind students of the pH indicator
Precipitate (a Solid is Formed): Using a zip-lock bag, add glue, water, food coloring and a tsp
of borax or liquid starch.
a New Odor is Produced: It only takes one experience with a rotten egg to learn that they smell
different that fresh eggs. When eggs and food spoil, they undergo a chemical change. The
change in odor is a clue to the chemical change
a Change in Temperature: Elephant Toothpaste Demonstration exothermic, so heat is
produced
catalyst on the side for 5 minutes (3 tablespoons of warm water to 1 tablespoon of active
dry yeast)
container with small opening for a greater impact. ½ cup of peroxide (40%)
drops of food coloring
squirt of dishwashing liquid (concentrated)
then pour catalyst and step back
How It Works
Hydrogen peroxide (H2O2) is a reactive molecule that readily decomposes into water
(H2O) and oxygen:
2H2O2 → 2H2O + O2(g)
In this demonstration, yeast
catalyzes the decomposition so that it proceeds much more rapidly than normal. The
dishwashing detergent captures the oxygen that is released, making foam. Food coloring
can color the film of the bubbles so that you get colored foam. In addition to being a nice
example of a decomposition reaction and a catalyzed reaction, the elephant
toothpaste demo is exothermic, so heat is produced.