Conservation of Mass
Word Problem Worksheet
Directions: Examine the data for each of the following reactions and answer the questions based on
your analysis of the data. Answer all questions using complete sentences.
Reaction #1
Reactants
Magnesium + Oxygen 
48 g
32 g
a)
b)
c)
d)
Products
Magnesium Oxide
80 g
What is the mass of each reactant?
What is the mass of the product?
What is the total mass of the reactants?
Does this experimental data support the law of conservation of mass? Explain.
Reaction #2
Reactants
Magnesium + Oxygen 
?g
16 g
Products
Magnesium Oxide
40 g
a) What is the mass of the product?
b) What amount of magnesium is needed to react with the 16 grams of oxygen to produce 40
grams of magnesium oxide? (Hint: set up a math problem then write your final answer using a
complete sentence.)
Reaction #3
Reactants
Magnesium + Oxygen 
12 g
8g
Products
Magnesium Oxide
?g
a) Assuming that magnesium and oxygen will react completely with one another, calculate the
mass of magnesium oxide that will be produced.
Reaction #4
Reactants
Magnesium + Oxygen 
48 g
50 g
Products
Magnesium Oxide + Oxygen
80 g
?g
1. Calculate the mass of oxygen that will be left over after the reaction of 48 grams of magnesium
with 50 grams of oxygen.
Balanced or Not?
Directions:
 For each equation, count the number of atoms of each element on the reactant side.
 Then count the number of atoms of each element on the product side.
 Next, determine if the equation is balanced or not.
 Using complete sentences, briefly explain your answer.
1. 2H2 + O2  2H2O
2. N2 + H2  NH3
3. S8 + O2  8SO3
4. 2HgO  2Hg + O2
5. CO2 + H2O  C6H12O6 + O2
6. Zn + 2HCl  ZnCl2 + H2
7. SiCl4 + 4H2O  H4SiO4 + HCl
8. C6H12O6 + 6O2  6CO2 + 6H2O
9. Na + H2O  NaOH + H2
10.C10H16 + Cl2  C + HCl
Balanced or Not?
Directions: For each equation, count the number of atoms of each element on the reactant side. Then
count the number of atoms of each element on the product side. Next, determine if the equation is
balanced or not. Using complete sentences, briefly explain your answer.
1. N2 + H2  NH3
2. S8 + O2  8SO3
3. 2HgO  2Hg + O2
4. CO2 + H2O  C6H12O6 + O2
5. Zn + 2HCl  ZnCl2 + H2
6. SiCl4 + 4H2O  H4SiO4 + HCl
7. C6H12O6 + 6O2  6CO2 + 6H2O
8. Na + H2O  NaOH + H2
Directions:
 For each equation, choose the answer choice that gives the missing coefficient that would
correctly balance the equation.
 Write a short explanation of your choice
1. N2 + ?H2  2NH3
a. 2
b. 3
c. 6
2. S8 + ?O2  8SO3
a. 8
b. 12
c. 6
3. ?HgO  2Hg + O2
a. 2
b. 1
c. 4
4. SiCl4 + 4H2O  H4SiO4 + ?HCl
a. 2
b. 8
c. 4
5. 4Fe + ?O2  2Fe2O3
a. 2
b. 3
c. 4