1. Chapter 9A Notes Stoichiometry
West Valley High School
General Chemistry
Mr. Mata

2. Standard 3e
Students will know how to calculate the mole or mass of a reactant or product from the mole or mass of one of the reactants or products.

3. Essential Question
How is stoichiometry used to relate reactants & products in a chemical reaction?

4. Stoichiometry Stoicheion = g. “element” Metron = g. “measure”
Stoichiometry = “to measure the elements”.
Stoichiometry - calculation of quantities of substances involved in chemical reactions.
Use coefficients of balanced chemical equations to show ratio of moles of reactants & products:

5. Two Types of Stoichiometry
Composition stoichiometry – mass relationships of elements in compounds.
Reaction stoichiometry – mass relationships between reactants and products in a chemical reaction.
Based on chemical equations and the Law of Conservation of Mass.

6. Steps to Stoichiometry
Start with a balanced chemical equation.
Use number of moles of reactants & products.
Two types of stoichiometry problems:
Mole A -> mole B
Gram A -> mole A -> mole B -> gram B

7. What does this equation mean?
N H NH3
1 mole of nitrogen (N2) reacts with
3 moles of hydrogen (H2) to form:
2 moles of ammonia (NH3)

8. N2 + 3H2 2NH3 Mole ratios: 1 mol N2 3 mol H2 3 mol H2 1 mol N2 or
2 mol NH3
1 mol N2
1 mol N2
2 mol NH3 or
2 mol NH3
3 mol H2
3 mol H2
2 mol NH3 or

9. Mole-Mole Calculations
Steps:
1. Write the balanced chemical equation.
2. Write moles of given reactant/product.
3. Multiply by the mole ratio:
given mol A x mol B = ___ mol B
mol A

10. N2 + 3H2 2NH3 3 mol H2 = 2 mol NH3 (mol : mol ratio)
Calculate the moles of NH3 that can be produced from 10.8 moles of H2.
3 mol H2 = 2 mol NH3 (mol : mol ratio)
10.8 mol H2 x 2 mol NH3 =
3 mol H2
= 7.2 mol NH3

11. N2 + 3H2 2NH3 25 mol N2 x 2 mol NH3 = 1 mol N2 = 50 mol NH3
Calculate the moles of NH3 that can be produced from 25 moles of N2.
1 mol N2 = 2 mol NH3 (mol : mol ratio)
25 mol N2 x 2 mol NH3 =
1 mol N2
= 50 mol NH3

12. N2 + 3H2 2NH3 3 mol H2 = 2 mol NH3 (mole : mole ratio)
Calculate the moles of NH3 that can be produced from 53.7 moles of H2.
3 mol H2 = 2 mol NH3 (mole : mole ratio)
53.7 mol H2 x 2 mol NH3 =
3 mol H2
= 35.8 mol NH3

13. Mole: Mole Problem __ Al2O3 -> __ Al + __ O2
Calculate the moles of Al that can be produced from 20 moles of Al2O3.
__ mol Al = __ mol Al2O3 (mol : mol ratio)
___ mol Al2O3 x mol Al =
mol Al2O3

14. Solution: 2 Al2O3 -> 4 Al + 3 O2
Calculate the moles of Al that can be produced from 20 moles of Al2O3.
4 mol Al = 2 mol Al2O3 (mol : mol ratio)
20 mol Al2O3 x mol Al =
2 mol Al2O3
40 mol Al