Review for Chemistry Exam
Chapter 9: Stoichiometry
Please answer the following questions on a separate sheet of paper.
*Be sure you understand the concepts involved in each question, do not try to
just memorize the facts!*
I. Definitions
1. What is the mole?
2. What is a mole ratio? How do you find it?
3. What is the molar mass? How do you find it?
4. What are the 3 steps to convert an known mass A to and unknown mass B?
1.
2.
3.
5. What is the limiting reactant? How do you find it?
6. What is the excess reactant? How do you find it?
7. What is the actual yield? How do you find it?
8. What is the theoretical yield? How do you find it?
9. What is the percent yield? How do you find it?
10. What is the percent error? How do you find it?
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II. Conversion Problems: Be sure to show all units and label your work!
1. Convert Moles to Moles
Hydrogen sulfide gas reacts with oxygen to produce sulfur dioxide gas and water:
2H2S(g) + 3O2(g) -- 2SO2(g) + 2H2O(g)
a. How many moles of oxygen gas are required to react with 5.6 moles of
hydrogen sulfide gas?
b. How many moles of sulfur dioxide gas will be produced by reacting 7.3 moles
of hydrogen sulfide gas with excess oxygen?
c. How many moles of sulfur dioxide gas will be produced by reacting 7.3 moles
of oxygen with excess hydrogen sulfide?
Mrs. Drurey
-1-
Newton South High School
Review for Chemistry Exam
Chapter 9: Stoichiometry
Iron (II) oxide reacts with oxygen to form Iron (III) oxide:
____FeO(s) + ___O2(g) -- ___Fe2O3(s)
a. Balance the equation with correct coefficients. What type of reaction is this?
b. How many moles of oxygen gas is required to react with 2.4 moles of iron (II)
oxide?
c. How many moles of iron (III) oxide will be produced when 9.2 moles of iron (II)
oxide react with excess oxygen?
d. How many moles of iron (III) oxide will be produced when 9.2 moles of oxygen
react with excess iron (III) oxide?
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2. Convert Mass to Mass
Hydrofluoric acid is used to etch glass by reacting with silica, SiO2, to produce
silicon tetrafluoride gas and water:
___SiO2(g) + ___HF(aq) -- ____SiF4(g) + ____H2O(l)
a. Balance the equation with correct coefficients. What type of reaction is this?
b. How many grams of hydrofluoric acid (HF) is needed to react with 5.68 grams
of silicon dioxide (SiO2)?
c. How many grams of water (H2O) are produced from 5.68 grams of SiO2?
Mrs. Drurey
-2-
Newton South High School
Review for Chemistry Exam
Chapter 9: Stoichiometry
Propane (C3H8) reacts with oxygen gas to produce
Carbon dioxide and water:
___C3H8(g) + ___O2(g) -- ___CO2(g) + ___H2O(g)
a. Balance the equation with correct coefficients. What type of reaction is this?
b. How many grams of oxygen are needed to react with 44.1 grams of propane?
c. How many grams of carbon dioxide are produced from 44.1 grams of
propane?
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3. Find the Limiting and Excess Reactants
Nitrogen gas combines with hydrogen gas to produce ammonia:
___N2(g) + ___H2(g) -- ___NH3(g)
a. Balance the equation with correct coefficients. What type of reaction is this?
b. If 5000 grams of nitrogen are mixed with 5000 grams of hydrogen gas,
calculate the mass of ammonia produced from this reaction.
c. Which is the limiting reactant?
d. Which is the excess reactant? How many moles and grams are excess?
Mrs. Drurey
-3-
Newton South High School
Review for Chemistry Exam
Chapter 9: Stoichiometry
Lithium metal combines with nitrogen gas to produce lithium nitride solid:
___Li(s) + ___N2(g) -- ___Li3N(s)
a. Balance the equation with correct coefficients. What type of reaction is this?
b. If 56.0 grams of lithium are mixed with 56.0 grams of nitrogen gas, calculate
the mass of lithium nitride produced from this reaction.
c. Which is the limiting reactant?
d. Which is the excess reactant? How many moles and grams are excess?
___________________________________________________________
4. Calculate the Percent Yield
Methanol is an alcohol that is produced by the reaction of carbon monoxide and
hydrogen gas (already balanced):
CO(g) + 2H2(g) -- CH3OH(l)
a. If If 6.5 x 104 grams of carbon monoxide are reacted with 8.5 x 103 grams of
hydrogen, calculate the theoretical yield of methanol.
b. If 4.0 x 104 grams of methanol are actually produced, calculate the percent
yield of methanol.
Mrs. Drurey
-4-
Newton South High School
Review for Chemistry Exam
Chapter 9: Stoichiometry
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III. Problem-Solving: Be sure to show all units and label your work in each
step of the problem!
2H2
+
O2 ------> 2H2O
1. Given: 50.0 grams of H2, 50.0 grams of O2, actual yield of H2O = 44.0 grams
a. Find: How many moles of H2, O2 and H2O are used in the reaction
b. Find: How many grams of H2, O2 and H2O are used in the reaction
c, d, e Find: The limiting reactant, excess reactant, percent yield of H2O
H2
O2
H2O
a. Moles
b. Mass
c. Limiting reactant
d. Excess reactant
(how much?)
e. Percent yield
4NH3
+
5O2 ------> 4NO +
6H2O
2. Given: 64 grams NH3, 64 grams of O2, actual yield NO = 52.9 grams
a. Find: How many moles of NH3, O2, NO, and H2O are produced in the reaction
b. Find: How many grams of NH3, O2, NO, and H2O are produced in the reaction
c, d, e Find: The limiting reactant, excess reactant, percent yield of NO
NH3
O2
NO
H2O
a. Moles
b. Mass
c. Limiting
reactant
d. Excess
reactant
e. Percent
yield of NO
Mrs. Drurey
-5-
Newton South High School