Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
The scouts are making s’mores out of toasted marshmallows, chocolate, and graham crackers.
1. What is wrong with the image below? The ingredients are unbalanced and
there is not enough to make four smores.
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
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)?
3
4. In general, what does a subscript (such as the “2” in H2) tell you about the molecule?
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, A subscript tells you how many atoms of an element are in a
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
Get the Gizmo ready:
Activity A:
• Check that the Synthesis reaction is selected and
Balancing that all coefficients are set to one. (The
equations coefficients are the numbers in the boxes.)
Introduction: The equation H2 + O2 H2O is unbalanced because there are two oxygen atomson
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 molecules, but you can
change the number of molecules that are used.
Question: How are chemical equations balanced?
1. Balance: Turn on Show histograms. The equation is balanced when there are equal
numbers of each type of atom represented on each side of the equation.
In the Gizmo, use the up and down arrows to adjust the numbers of hydrogen, oxygen, and
water molecules until the equation is balanced. When you are done, turn on Show
summary to check your answer.
Write the balanced equation here: 2 H2 + O2 2 H2O
2. Solve: Turn off Show summary. Use the Choose reaction drop down menu to see other
equations, and balance them. Check your answers and then write the balanced equations.
2 Al + 6 HCl 2 AlCl3 + 3 H2
2 NaCl 2 Na + Cl2
Na2S + 2 HCl 2 NaCl + H2S
CH4 + 2 O2 CO2 + 2 H2O
3. Practice: Balance the following chemical equations. (These equations are not in the Gizmo.)
A. 2 Na + Cl2 2 NaCl
B. 2 Na + 2 H2O 2 NaOH + H2
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