Student Exploration: Balancing Chemical Equations
Learning Objectives
Students will…
• Adjust coefficients to balance a chemical equation.
• Classify chemical equations as combination (synthesis), decomposition, single
replacement, or double replacement.
Vocabulary: coefficient, combination, compound, decomposition, double replacement, element,
molecule, product, reactant, single replacement, subscript
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?
Answer: 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 floatingmolecules
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?Answer:
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 isequal to
the number of each type on the right side. Is this reaction balanced? No
, Get the Gizmo ready:
Activity A:
• Check that the Combination reaction is selected
Balancing
and 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 equalnumbers
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, andwater
molecules until the equation is balanced. When you are done, turn on Show summary to check your
answer.
Write the balanced equation here: 2H2 + 1O2 2H2O
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 2Na + 1Cl2
1 Na2S + 2 HCl 2 NaCl + 1 H2S
3. Practice: Balance the following chemical equations. (These equations are not in the Gizmo.)
A. 2 Na + 1 Cl2 2 NaCl
B. 2 Na + 2 H2O 2 NaOH + 1 H2
C. 2 Mg + 1 O2 2 MgO
D. 2 KClO3 2 KCl + 3 O2
E. 2Al + 3 CuO 1 Al2O3 + 3 Cu
F. 1 CaCO3 1 CaO + 1CO2
G. 1 I2 + 2Na2S2O3 2 NaI +1Na2S4O6
H. 6 Mg + 1 P4 2 Mg3P2
Learning Objectives
Students will…
• Adjust coefficients to balance a chemical equation.
• Classify chemical equations as combination (synthesis), decomposition, single
replacement, or double replacement.
Vocabulary: coefficient, combination, compound, decomposition, double replacement, element,
molecule, product, reactant, single replacement, subscript
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?
Answer: 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 floatingmolecules
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?Answer:
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 isequal to
the number of each type on the right side. Is this reaction balanced? No
, Get the Gizmo ready:
Activity A:
• Check that the Combination reaction is selected
Balancing
and 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 equalnumbers
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, andwater
molecules until the equation is balanced. When you are done, turn on Show summary to check your
answer.
Write the balanced equation here: 2H2 + 1O2 2H2O
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 2Na + 1Cl2
1 Na2S + 2 HCl 2 NaCl + 1 H2S
3. Practice: Balance the following chemical equations. (These equations are not in the Gizmo.)
A. 2 Na + 1 Cl2 2 NaCl
B. 2 Na + 2 H2O 2 NaOH + 1 H2
C. 2 Mg + 1 O2 2 MgO
D. 2 KClO3 2 KCl + 3 O2
E. 2Al + 3 CuO 1 Al2O3 + 3 Cu
F. 1 CaCO3 1 CaO + 1CO2
G. 1 I2 + 2Na2S2O3 2 NaI +1Na2S4O6
H. 6 Mg + 1 P4 2 Mg3P2
