What is Stoichiometry?
Chemistry Unit 10: Guided Notes
New Skills:
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Identify mole ratios in a balanced equation
Calculate moles and mass stoichiometry
Determine limiting reactant
Calculate percent yield
Academic Language:
Actual yield
Excess reactant
Limiting reactant
Mole ratio
Percent yield
Stoichiometry
Theoretical yield
Unit 10 Homework:
CALM: http://calm.indiana.edu/
10.1 Defining Stoichiometry
 CALM: 5 questions
 p371 #1,2
 p372 #4,5,6,9
10.2 Stoichiometric Calculations
 CALM: 5 questions
 p393 #61, 62, 63
10.3 Limiting Reactants
 CALM: 5 questions
 p383, #23,24
10.4 Percent Yield
 CALM: 5 questions
 p387 #28,29,30
10:5 Accumulating Content and Skills
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What is Stoichiometry?
Chemistry Unit 10: Learning Goals and Objectives
Stoichiometry – Mass relationships in chemical reactions confirm the law of conservation
of mass.
10.1 Defining Stoichiometry – the amount of each reactant present at the start of a chemical
reaction determines how much product can form.
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
Describe the types of relationships indicated by a balanced equation.
State the mole ratios from a balanced equation.
10.2 Stoichiometric Calculations – The solution to every stoichiometric problem requires a
balance chemical equation.
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List the sequence of steps used in solving stoichiometric problems.
Solve stoichiometric problems.
10.3 Limiting Reactants – A chemical reaction stops when one of the reactants is used up.
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Identify the limiting reactant in a chemical equation.
Identify the excess reactant, and calculate the amount remaining after the reaction is
complete.
Calculate the mass of a product when the amounts of more than one reactant are
given.
10.4 Percent Yield – Percent yield is a measure of the efficiency of a chemical reaction.
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
Calculate the theoretical yield of a chemical reaction from data.
Determine the percent yield for a chemical equation.
10.5 Accumulating Content and Skills– Chemistry content is continuous and builds on prior
knowledge and skills. This section will combine this unit with previous units.
 Apply knowledge and skills from previous units to content learned in this unit.
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10.1 Defining Stoichiometry – the amount of each reactant present at the start of a
chemical reaction determines how much product can form.
Objective: Describe the types of relationships indicated by a balanced equation.
Stoichiometry - is the study of quantitative relationships between the amounts of products
formed by a chemical reaction.



Practice Problem #1: C3H8(g) + 5O2(g)  3CO2 + 4H2O(g)
Moles:
Mass:
(molecules are not necessarily balanced on each side. Atoms, moles and mass are)
Objective: State the mole ratios from a balanced equation.
Mole Ratio – is a ratio between the numbers of moles of any two substances in a balanced
chemical equation.

Practice Problem #2: 4Al(s) + 3O2(g)  2Al2O3(s)
Mole Ratios
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3Fe(s) + 4H2O(l)  Fe3O4 + 4H2(g)
Mole Ratios
2HgO(s)  2Hg(l) + O2(g)
Mole Ratios
10.2 Stoichiometric Calculations – The solution to every stoichiometric problem
requires a balance chemical equation.
Objective: List the sequence of steps used in solving stoichiometric problems.
Steps to solving stoichiometric problems:
1.
2. Determine the starting point of the calculations
a.
3.
4. Convert moles to requested units if needed.
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Objective: Solve stoichiometric problems.
Practice Problem #3, Moles to Moles: When burning propane (C3H8), carbon dioxide is
produced. How many moles of CO2 are produced when 10.0 mol of C3H8 are burned in
excess oxygen?
Calculate the moles of CS2 and H2S produced when 1.5 mol S8 is used?
CH4(g) +
S8(s) 
CS2(l) +
H2S(g)
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Sulfuric acid (H2SO4) is formed when sulfur dioxide (SO2) reacts with oxygen
and water. How many moles of H2SO4 are produced from 12.5 moles of SO2?
How many moles of O2 are needed?
Practice Problem #4, Moles to Mass: Sodium chloride is decomposed into the elements
sodium and chlorine. How much chlorine gas, in grams is obtained when 2.50 mol of
sodium chloride are used?
Practice Problem #5, Mass to Mass: Acid rain (H2SO4) is formed from SO2, O2 and H2O.
If 2.5g of SO2 reacts with excess oxygen and water, how much H2SO4 is produced?
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10.3 Limiting Reactants – A chemical reaction stops when one of the reactants is used up.
Objective: Identify the limiting reactant in a chemical equation.
Objective: Identify the excess reactant, and calculate the amount remaining after the reaction is
complete.
Limiting reactant – limits the extent of the reaction.
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Excess reactants – reactants leftover when a reaction stops.
Example:
Supplies
First Aid Kits
500 bandaids
24 bandaids
85 rolls of gauze
4 gauze rolls
24 first aid ointments
1 first aid ointment
24 cans of burn sprays
1 can of burn spray
65 rolls of tape
3 rolls of tape
50 ace bandages
2 ace bandages
How many first aid kits can be made from the supplies?
What supplies are left?
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Objective: Calculate the mass of a product when the amounts of more than one reactant are
given.
Determining the product when a reactant is limiting:
1.
2.
3.
a. Moles reacted
b. Mass reacted
c. Excess remaining
Practice Problem #6: If 200.0g of sulfur reacts with 100.0g of chlorine, what mass of
disulfur dichloride is produced?
S8(l) + 4Cl2(g)  4S2Cl2(l)
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10.4 Percent Yield – Percent yield is a measure of the efficiency of a chemical reaction.
Objective: Calculate the theoretical yield of a chemical reaction from data.
Objective: Determine the percent yield for a chemical equation.
Theoretical yield – is the maximum amount of product that can be produced from a given
amount of reactant.

Actual yield – is the amount of product produced when the chemical reaction is carried out in
an experiment
Percent yield – is the ratio of the actual yield expressed as a percent.
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%yield =
actual yield(exp erimental)
x100%
theoretical yield(calculated)
Practice Problem #7: Solid silver chromate (AgCrO4) forms when potassium chromate
(K2CrO4) is added to a solution containing .500g of silver nitrate (AgNO3). Determine the
theoretical yield of Ag2CrO4. Calculate the percent yield if the reaction yields .455g of
Ag2CrO4.
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10.5 Accumulating Content and Skills– Chemistry content is continuous and builds on
prior knowledge and skills. This section will combine this unit with previous units.
Objective: Apply knowledge and skills from previous units to content learned in this unit.
Practice Problem #8: When an antacid tablet dissolves in water, the fizz is due to a
reaction between sodium hydrogen carbonate (baking soda), also called sodium
bicarbonate, and citric acid (H3C6H5O7). What are the masses of the products if there
is 1.00 gram of each reactant in a tablet. Use the net ionic equation to solve this
problem.
What is the percent yield if only 1.25g of gas was produced? How does this affect the
resulting mass of your other product?
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Study Guide and Key Concepts
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Balanced chemical equations can be interpreted in terms of moles, mass, and
representative particles (atoms, molecules, formula units).
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The law of conservation of mass applies to all chemical reactions.
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Mole ratios are derived from the coefficients of a balanced chemical equation. Each
mole ratio relates the number of moles of one reactant or product to the number of
moles of another reactant or product in the chemical reaction.
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Chemists use stoichiometric calculations to predict the amounts of reactants used and
products formed in specific reactions.
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The first step in solving stoichiometric problems is writing the balanced chemical
equation.
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Mole ratios derived from the balanced chemical equation are used in stoichiometric
calculations.
Stoichiometric problems make use of mole ratios to convert between mass and
moles.
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The limiting reactant is the reactant that is completely consumed during a chemical
reaction. Reactants that remain after the reaction stops are called excess reactants.

To determine the limiting reactant, the actual mole ratio of the available reactants
must be compared with the ratio of the reactants obtained from the coefficients in the
balanced chemical equation.
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Stoichiometric calculations must be based on the limiting reactant.
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The theoretical yield of a chemical reaction is the maximum amount of product that
can be produced from a given amount of reactant. Theoretical yield is calculated from
the balanced chemical equation.
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The actual yield is the amount of product produced. Actual yield must be obtained
through experimentation.
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Percent yield is the ratio of actual yield to theoretical yield expressed as a percent.
High percent yield is important in reducing the cost of every product produced
through chemical processes.
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