Chapter 12- Stoichiometry
What is stoichiometry?


“stochio” = Greek for element
“metry” = measurement
 Converting a known quantity of one substance into
an unknown quantity of another substance using a
BALANCED EQUATION
 Interpreting a balanced equation:
 N2 + 3 H2  2 NH3
 Coefficients represent moles or representative
particles. (We will use moles)
 1 mole N2 + 3 moles H2 yields 2 moles NH3
Mole Ratios
 Heart of stoichiometry; must be used in
EVERY calculation you do
 Ratio of any two substances from balanced
equation
 Example: N2 + 3 H2  2 NH3
Write all mole ratios for:
 3 NO2 + H2O  2HNO3 + NO
Analogy
 Think of a balanced equation as a recipe.
 Ex: Making a turkey and cheese sandwich
 2 slices of bread + 3 slices of turkey + 1 slice of
cheese  1 sandwich
 How could you make two sandwiches?
 How could you make ½ of a sandwich?
Stoichiometry Question 1
4NH3 + 5O2  6H2O + 4NO
 How many moles of H2O are produced if
2.00 moles of O2 are used?
Stoichiometry Question 2
4NH3 + 5O2  6H2O + 4NO
 How many moles of NO are produced in
the reaction if 15 mol of H2O are also
produced?
Mole Bridge
4 NH3 + 5 O2  6 H2O + 4 NO
MOLE RATIO
(coefficients)
Stoichiometry Question 3
4 NH3 + 5 O2  6 H2O + 4 NO
How many grams of H2O are produced if 2.2
mol of NH3 are combined with excess oxygen?
MOLE RATIO
(coefficients)
(NH3)
(H2O)
Stoichiometry Question 3
4 NH3 + 5 O2  6 H2O + 4 NO
How many grams of H2O are produced if 2.2
mol of NH3 are combined with excess oxygen?
Stoichiometry Question 4
4 NH3 + 5 O2  6 H2O + 4 NO
How many grams of NO are produced if 12 g
of O2 is combined with excess ammonia?
Moving along the stoichiometry path
 We always use the same type of information to
make the jumps between steps:
Molar mass of x
Molar mass of y
grams (x)  moles (x)  moles (y)  grams (y)
Mole ratio from
balanced equation
Practice!
Try these on your own - 4 NH3 + 5 O2  6 H2O + 4 NO
a) How many moles of H2O can be made using 1.6 mol NH3?
b) What mass of NH3 is needed to make 0.75 mol NO?
c) How many Liters of NO can be made from 47 g of NH3?