Stoichiometry Notes
Review of Moles
Determine the molar mass of Ca3(PO4)2
How many moles of H2O are in 9.87 grams of H2O?
How many molecules are in 87.9 grams of nitrogen dioxide?
How many oxygen ions are in 7.67 grams of potassium oxide?
What is the density of oxygen gas at STP?
What is the volume of 86.9 grams of carbon dioxide at STP?
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__________________– calculation of quantities in chemical reactions.
Calculations using balanced equations are called stoichiometric calculations.
1 N2 + 3 H2 → 2 NH3
One molecule of nitrogen reacts with 3 molecules of hydrogen to produce 2 molecules
of ammonia, NH3.
We could also say 1 mole of nitrogen reacts with 3 moles of hydrogen to product 2
moles of ammonia.
OR
2 moles of nitrogen will react with 6 moles of hydrogen to produce 4 moles of ammonia.
How many moles of ammonia can be produced if you have one mole of nitrogen gas and 3
moles of hydrogen gas?
How many moles of ammonia can be produced if you have one mole of nitrogen gas and 6
moles of hydrogen gas?
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Keep in mind:
1. The ratio of moles in any chemical reaction will remain constant.
a. Ex) 1 N2 + 3 H2 → 2 NH3
1:3:2
2. The mass of the reactants will equal the mass of the products
3. The number of atoms of each element in the reactant will equal the number of
atoms of each element in the product
4. The number of moles in the reactant does NOT have to equal the number of moles
in the product.
What have we learned so far?
1. Calculations using moles, ions, atoms, molecules, and grams.
2. Balance Chemical Reactions.
3. Predict products of chemical reactions.
Mole-Mole Calculations
How many moles of sodium oxide will react with 1.25 moles of water to produce sodium
hydroxide?
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Mole-Mole Calculations
How many moles of water will be produced from the reaction of 2.35 moles of butane
reacts with excess oxygen?
Mole-Mole Calculations
How many moles of hydrochloric acid does it take to produce 0.825 moles of water when
hydrochloric acid reacts with calcium hydroxide?
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Calculations Steps
1. Determine the known and unknown.
2. Convert the known to moles
3. Use the balanced reaction to determine the relationship between known and
unknown. Unknown is always numerator and known is denominator
4. Convert your unknown to the correct units based on what the problem is asking.
Mass to Mass Calculations
How many grams of silver chloride will be produced when 7.98 g of silver nitrate reacts
with excess sodium chloride?
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Mass to Mass Calculations
How many grams of carbon dioxide are produced when 35.7 grams of potassium
carbonate decomposes?
Mass to Mass Calculations
Propane combusts in the presence of oxygen to produce 75.0 moles of carbon dioxide.
How many grams of water would you also expect to be produced in this reaction?
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Mass to Mass Calculations
How many grams of copper are produced when 11.5 grams of iron (II) metal reacts with
copper (II) chloride?
How many grams of ammonium phosphate are required to produce 147 g of calcium
phosphate when ammonium phosphate reacts with calcium nitrate?
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How many grams of water are produced when 75.9 grams of iron (III) hydroxide
decomposes?
Volume and stoichiometry
A tank containing 65.8 L of propane is allowed to burn. How many liters of water will be
released?
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How many liters of oxygen will react with 0.40 L of hexane?
How many liters of sulfur dioxide are produced when sulfurous acid decomposes?
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If 4.79 L of carbon dioxide reacts with potassium oxide, how many grams of potassium
carbonate will be produced?
Limiting reagent or limiting reactant – substance in the reactants that limits how
much of the product(s) can be made.
1. The reactants will combine until one of the reactants is used up.
2. The reaction will only continue if you add more of the reactant that was used up
first.
3. Usually you will be asked to determine how much of a product can be produced.
4. The reactant that produces the smallest amount of product is the limiting
reactant.
5. The amount of product formed from the limiting reactant tells you the most
product that can be made.
6. You can also find out how much of the excess reactant remains once the
reaction stops.
Excess reactant – substance that is left after the reaction has stopped.
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How many grams of aluminum oxide will be produced when 40.0 grams of aluminum and
10.0 grams of oxygen react?
What is the limiting reagent/reactant?
What is the excess reagent/reactant?
How much aluminum oxide can be produced?
How many grams of excess reactant will be left after the reaction goes to completion?
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When 75 g barium hydroxide reacts 25 g chromium (III) nitrate, how many grams of
barium nitrate could be produced?
What is the limiting reagent/reactant?
What is the excess reagent/reactant?
How much barium nitrate can be produced?
How many grams of excess reactant will be left after the reaction goes to completion?
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Calculating Percent Yield
1. When doing any experiment it is easy for something wrong to happen.
2. It is unlikely for anyone to do an experiment where there are no errors.
3. When you go through a mass-mass (or grams to grams) calculation the value you
determine is the theoretical yield.
4. Theoretical Yield – maximum amount of product that could be formed from the
amounts of reactants given in the problem.
5. Actual Yield – amount that actually forms as a result of conducting a laboratory
experiment.
6. Percent Yield – ratio of the actual yield to the theoretical yield times 100.
7. Percent Yield =
Actual Yield
x 100
Theoretical Yield
Reasons not to get 100% Yield
1. Reactions do not always go to completion
2. Impure reactants
3. Side reactions or competing reactions
4. Loss of product during filtration or in transferring between different
containers.
5. Not heated long enough to remove all water.
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What is the percent yield of copper if 4.65 g of copper is actually produced when 1.87g
of aluminum reacts with an excess of copper (II) sulfate?
What is the percent yield of an experiment that reacts 20.0 g of copper (II) sulfate with
an excessive amount of aluminum to form 12.5 g of aluminum sulfate?
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