Balancing Chemical Equations: Answer Keys

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Balancing Chemical Equations

Answer Key

Vocabulary: coefficient, combination, compound, decomposition, double replacement, element, molecule, product, reactant, single replacement, subscript

Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
[Note: The purpose of these questions is to activate prior knowledge and get students thinking.
Students are not expected to know the answers to the Prior Knowledge Questions.]
The scouts are making s’mores out of toasted marshmallows, chocolate, and graham crackers.
1. What is wrong with the image below? There aren’t enough ingredients to make four s’mores.

2. Assuming a s’more requires two graham crackers, one marshmallow, and one piece of chocolate, how many s’mores could you make with the ingredients shown? 2 (or 2.5)
Gizmo Warm-up
In a chemical reaction, reactants interact to form products.
This process is summarized by a chemical equation. In the
Balancing Chemical Equations Gizmo™, look at the floating molecules below the initial reaction: H2 + O2  H2O.
1. How many atoms are in a hydrogen molecule (H2)? 2
2. How many atoms are in an oxygen molecule (O2)? 2
3. How many hydrogen and oxygen atoms are in a water molecule (H2O)? 2 H, 1 O
4. In general, what does a subscript (such as the “2” in H2) tell you about the molecule?
The subscript tells you how many atoms of each element are in the molecule.

5. A chemical equation is balanced if the number of each type of atom on the left side is equal to the number of each type on the right side. Is this reaction balanced? No

Activity A:
Balancing
equations

Get the Gizmo ready:
 Check that the Combination reaction is selected and that all coefficients are set to one. (The coefficients are the numbers in the boxes.)

Introduction: The equation H2 + O2  H2O is unbalanced because there are two oxygen atoms on the reactants side of the equation, and only one on the products side of the equation. To balance the equation, you cannot change the structure of any of the

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