StoichiometryChapters 7 and 9

Stoichiometry ObjectivesObjectives: students will be able to…1. calculate the molar mass of a compound.2. calculate the percent composition by mass of an element in a compound.3. calculate the mass of an element present in a sample of a compound.4. distinguish between an element's atomic mass and molar mass.5. calculate the mass of a substance given the number of moles present.6. calculate the number of moles present given the mass of a sample.7. determine the mole ratio of compounds in a balanced chemical equation.8. calculate stoichiometric quantities when given a balanced chemical equation.9. 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)

• actual yield• molar mass• percent yield• empirical formula• Mole• Stoichiometry

• 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 Problems1. Identify what you know and what you do not know and write it down.2. Convert any masses given to moles.

• Mass of substance (g) = Number of Moles

Molar Mass of substance (g/mol)

3. 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 Practice1. 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)

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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)

Basic Stoichiometry Practice …continuedWe

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)

Basic Stoichiometry Practice …continuedWe

Basic Stoichiometry Practice …continued4. 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)

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Homework1. 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.