1. Stoichiometry

2. Stoichiometry Consider the chemical equation: 4NH3 + 5O2  6H2O + 4NO
“stochio” = Greek for element
“metry” = measurement
Stoichiometry is about measuring the amounts of elements and compounds involved in a reaction.
Consider the chemical equation:
4NH3 + 5O2  6H2O + 4NO
There are several numbers involved.
What do they all mean?

3. Stoichiometry 4NH3 + 5O2  6H2O + 4NO NH3 O2 H2O NO
Recall that Chemical formulas represent numbers of atoms
NH3
1 nitrogen and 3 hydrogen atoms O2
2 oxygen atoms
H2O
2 hydrogen atoms and 1 oxygen atom NO
1 nitrogen atom and 1 oxygen atom

4. Recall that Chemical formulas are balanced with coefficients
Stoichiometry
4NH3 + 5O2  6H2O + 4NO
Recall that Chemical formulas are balanced with coefficients
4 X NH3
= 4 nitrogen + 12 hydrogen
5 X O2
= 10 oxygen
6 X H2O
= 12 hydrogen + 6 oxygen
4 X NO
= 4 nitrogen + 4 oxygen

5. Recall that Chemical formulas have molar masses:
Stoichiometry
4NH3 + 5O2  6H2O + 4NO
Recall that Chemical formulas have molar masses:
NH3
17 g/mol O2
32 g/mol
H2O
18 g/mol NO
30 g/mol

6. Stoichiometry 4NH3 + 5O2  6H2O + 4NO
With Stoichiometry we find out that
4 : 5 : 6 : 4
do more than just multiply atoms.
4 : 5 : 6 : 4
Are what we call a mole ratio.
What is the mole ratio for O2 to NO?
What is the mole ratio for O2 to H2O?

7. Mole Ratio
Shows the relationship between two of the substances in a balanced equation
Derived from the coefficients of any two substances in the equation

8. Stoichiometry Question (1)
4NH3 + 5O2  6H2O + 4NO
How many moles of H2O are produced if 2.00 moles of O2 are used?
6 mol H2O
5 mol O2
2.00 mol O2 =
2.40 mol H2O
Notice that a correctly balanced equation is essential to get the right answer

9. Stoichiometry Question (2)
4 NH O2  6 H2O NO
How many moles of NO are produced in the reaction if 15 mol of H2O are also produced?
4 mol NO
6 mol H2O
15 mol H2O =
10. mol NO

10. Mole-Mole Stoichiometry Practice N2 + 3 H2 → 2 NH3
a) How many moles of N2 are needed to create 12 moles of NH3?
b) How many moles of H2 are needed to create 12 moles of NH3?
c ) How many roads must a man walk down before you call him a man?

11. Stoichiometry Island Diagram
Known Unknown
Substance A Substance B
Mass
Mass
1 mole = molar mass (g)
1 mole = molar mass (g)
Use coefficients
from balanced
chemical equation
Volume
Mole
Mole
Volume
1 mole = STP
1 mole = STP
(gases)
(gases)
1 mole = x 1023 particles
(atoms or molecules)
1 mole = x 1023 particles
(atoms or molecules)
Particles
Particles
Stoichiometry Island Diagram

12. Mass, Volume, Mole Relationship