Stoichiometry
Chapters 7 and 9
Stoichiometry Objectives
Objectives: students will be able to…
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calculate the molar mass of a compound.
calculate the percent composition by mass of an element in a compound.
calculate the mass of an element present in a sample of a compound.
distinguish between an element's atomic mass and molar mass.
calculate the mass of a substance given the number of moles present.
calculate the number of moles present given the mass of a sample.
determine the mole ratio of compounds in a balanced chemical equation.
calculate stoichiometric quantities when given a balanced chemical equation.
identify the limiting reagent and calculate the quantity of products produced in
such a reaction.
10. calculate theoretical yield, actual yield, and percent yield.
11. determine the empirical formula of a compound.
12. determine the molecular formula of a compound.
Stoichiometry Vocabulary
(12 Words)
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actual yield
molar mass
percent yield
empirical formula
Mole
Stoichiometry
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excess reagent
mole ratio
theoretical yield
limiting reagent
percent composition
molecular formula
Stoichiometry Notes
• Stoichiometry is a process used by chemists to make
predictions about the quantities of substances that
react and are given off as products in chemical
reactions and relating those quantities to one another.
• Stoichiometry relates reactants to products in amounts
not masses.
– Therefore the problems are worked in terms of moles not
grams.
– However, the information both provided and requested is
often in terms of grams.
– Therefore, the ability to convert between these two
quantities is essential.
Steps to Solve Stoichiometry Problems
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Identify what you know and what you do not know and write it down.
Convert any masses given to moles.
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Mass of substance (g)
= Number of Moles
Molar Mass of substance (g/mol)
Determine the Mole Ratio needed.
• Coefficient of unknown substance in BALANCED chemical equation
Coefficient of known substance in BALANCED chemical equation
• mol unknown molecule
# mol known molecule
• # mol comes from BALANCED chemical equation NOT the problem itself.
4.
Use the mole ratio to determine the amount of product the known
reactant will produce.
• Known Moles X Mole Ratio = Moles of Product
5.
Convert moles of product to grams.
• Number of Moles X Total Molar Mass = Mass of substance (g)
Basic Stoichiometry Practice
1. How many moles of sodium will react with
water to produce 4.0 mol of hydrogen in the
following reaction? (8.0 mol Na)
2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
I
We
Basic Stoichiometry Practice …continued
2. Aluminum will react with sulfuric acid in the
following reaction. How many moles of sulfuric
acid will react with 18 moles of Al? (27 mol
H2SO4)
2Al(s) + 3H2SO4(l) → Al2(SO4)3(aq) + 3H2(g)
We
Basic Stoichiometry Practice …continued
3. Aluminum will react with sulfuric acid in the
following reaction. Based on your previous
answer, how many moles of each product will be
produced? (27 mol H2 and 9 mol Al2(SO4)3)
2Al(s) + 3H2SO4(l) → Al2(SO4)3(aq) + 3H2(g)
You
Basic Stoichiometry Practice …continued
4. How many moles of lithium chloride will be
formed in the reaction of chlorine with 0.046 mol
of lithium bromide in the following reaction?
(0.046mol LiCl)
2LiBr(aq) + Cl2(g) → 2LiCl(aq) + Br2(l)
Homework
1. Propane burns in excess oxygen according to the
following reaction:
C3H8 +5O2 → 3CO2 + 4H2O
a. How many moles of CO2 and H2O are formed from 3.85
moles of propane?
b. If 0.647 moles of oxygen is used in the burning of propane,
how many moles of CO2 and H2O are produced? How many
moles of propane are consumed?
2. How many moles of ammonium sulfate can be made
from the reaction of 30.0 mol of NH3 with H2SO4
according to the following equation?
2NH3 + H2SO4 → (NH4)2SO4
3. Complete any unfinished worksheets.