Chemistry
Chapter 9
Stoichiometry
What is stoichiometry?
• Stoichiometry = shows relationships between
masses of elements in compounds OR
between the reactants and products of
chemical reaction.
• There are different types of reactionstoichiometry problems.
• The type is determined by information given
in the problem and information you are
expected to find.
All Reaction-Stoichiometry
Problems Require:
• Correctly written balanced equation
• Mole ratio from a balanced equation
• Mole Ratio – conversion factor that relates
amounts in moles of any two substances
involved in a chemical reaction.
(remember: coefficients represent moles!)
• Example: 2 Al2O3(l) 4 Al(s) + 3O2(g)
Write all possible mole ratios for
this balanced equation:
2HgO (s)  2Hg (l) + O2 (g)
Mole-Mole Stoichiometry
Calculations
• Mole-Mole means you are given a known
amount of moles of one substance and asked
to find the number of relative moles of
another substance.
2 Al2O3(l) 4 Al(s) + 3O2(g)
This reaction shows that aluminum oxide decomposes
into 4 moles of aluminum and 3 moles of oxygen.
If the reaction actually yields 25 moles of Al how many
moles of oxygen would also be produced? (Mole-Mole Problem)
1. Make sure this is a correctly written and balanced equation.
2. Determine the balanced equation mole ratio that exists
between the 2 identified substances
3. Set up problem with mole ratios from balanced equation
equal to mole ratios from problem.
4. Solve
2 Al2O3(l) 4 Al(s) + 3O2(g)
You have 13.0 mol of aluminum oxide; how
many moles of aluminum will this
produce?
2 Al2O3(l) 4 Al(s) + 3O2(g)
You have 30.4 mol of Al; how many moles of
oxygen are produced?
2HgO (s)  2Hg (l) + O2 (g)
To yield 20.5 mol of oxygen; how many
moles of HgO are required?
Mass-Mass Stoichiometry
Calculations
• These are the most practical calculations
because you cannot directly measure moles.
• However---they rely on moles ratios from the
balanced equations.
• To repeat: YOU MUST HAVE MOLE RATIOS TO
SOLVE MASS-MASS CALCULATIONS!!!
Tin II fluoride, SnF2, is used in some toothpastes. It is made by
the reaction of tin with hydrogen fluoride according to the
following equation.
Sn(s) + 2HF(g)  SnF2 (s) + H2(g)
How many grams of SnF2 are produced from the reaction of
30.00 g of HF with Sn?
1. Is this a correct written and balanced equation?
2. Identify the mole ratio that exists between the 2 substances
identified in the problem.
3. Set up the problem with the mole ratio equal to the mass ratio
identified in the problem.
4. Substitute molar mass values for the equation mole ratio.
5. Solve.
Sodium hydroxide reacts with hydrochloric acid in a double
replacement reaction.
How many grams of sodium chloride can be produced if you start
with 75 grams of sodium hydroxide?
1. Write a correct and balanced equation?
2. Identify the mole ratio that exists between the 2 substances
identified in the problem.
3. Set up the problem with the mole ratio equal to the mass ratio
identified in the problem.
4. Substitute molar mass values for the equation mole ratio.
5. Solve.