1. Unit 4: Stoichiometry
Stoichiometry

2. Chemical Equations and the Mole
Remember:
a chemical equation is like a recipe – it tells you the ingredients (reactants) you need to make certain products
chemical equations tell you the relative quantities of reactants and products in a reaction

3. Chemical Equations and the Mole
How many moles do you have of each of the following?
Frame (F):
Seat (S):
Wheel (W):
Handlebar (H):
Pedal (P):
Tricycle (FSW3HP2):
1 mole
3 moles
2 moles

4. Chemical Equations and the Mole
Example:
If you had 4 moles of S and an excess of all the other reactants, how many tricycles (FSW3HP2) could you make?
We can apply the tricycle example to chemical reactions.

5. Stoichiometry
Stoichiometry: Using a known amount of one substance to predict how much of a reactant will be used or how much of a product will be produced.
You can use stoichiometry to answer questions like:
Calculate the number of grams of NH3 produced by the reaction of 5.40 g of nitrogen with an excess of hydrogen.
N2 + H2 → NH3

6. Stoichiometry – The Box Method
Calculate the number of grams of NH3 produced by the reaction of 5.40 g of nitrogen with an excess of hydrogen.
N H2 → 2NH3
Step 1: Balance the equation.

7. Stoichiometry – The Box Method
Calculate the number of grams of NH3 produced by the reaction of 5.40 g of nitrogen with an excess of hydrogen.
N H2 → 2NH3
grams
5.40 g *
molar mass
28.02 g/mol
g/mol
moles
Step 2: Construct the box and fill in known information (starting amount and molar masses).

8. Stoichiometry – The Box Method
Calculate the number of grams of NH3 produced by the reaction of 5.40 g of nitrogen with an excess of hydrogen.
N H2 → 2NH3
grams
5.40 g
*6.54 g
molar mass
28.02 g/mol
g/mol
moles
0.192 mol
0.384 mol
MORE x 2/1
Step 3: Calculate missing information until you determine what the problem is asking you to find.

9. Stoichiometry – The Box Method
Calculate the number of grams of NH3 produced by the reaction of 5.40 g of nitrogen with an excess of hydrogen.
N H2 → 2NH3
grams
5.40 g
*6.54 g
molar mass
28.02 g/mol
g/mol
moles
0.192 mol
0.384 mol
MORE x 2/1
Step 3: Calculate missing information until you determine what the problem is asking you to find.

10. Stoichiometry – Practice!
How many grams of water would be produced from 60 grams of H2 and an excess of O2?
__H2 + __O2 → __H2O

12. Stoichiometry
You can use stoichiometry to answer questions like:
Calculate the number of grams of NH3 produced by the reaction of 5.40 g of hydrogen with an excess of nitrogen.
N2 + H2 →NH3
Steps:
Balance the equation.
Convert mass to moles.
3. Convert moles of ‘known’ to moles of ‘unknown’ using the mole ratios (coefficients) from the balanced equation.
4. Convert moles of ‘unknown’ to mass ‘unknown’.

13. Stoichiometry – Step 1 N2 + H2 →NH3
Calculate the number of grams of NH3 produced by the reaction of 5.40 g of hydrogen with an excess of nitrogen.
N2 + H2 →NH3
Step 1: Balance the equation.

14. Stoichiometry – Step 2 N2 + H2 →NH3
Calculate the number of grams of NH3 produced by the reaction of 5.40 g of hydrogen with an excess of nitrogen.
N2 + H2 →NH3
Step 2: Convert mass to moles.

15. Stoichiometry – Step 3 N2 + H2 → NH3
Calculate the number of grams of NH3 produced by the reaction of 5.40 g of hydrogen with an excess of nitrogen.
N2 + H2 → NH3
Step 3: Convert moles of ‘known’ to moles of ‘unknown’ using the mole ratios (coefficients) from the balanced equation.

16. Stoichiometry – Step 4 N2 + H2 →NH3
Calculate the number of grams of NH3 produced by the reaction of 5.40 g of hydrogen with an excess of nitrogen.
N2 + H2 →NH3
Step 4: Convert moles of ‘unknown’ to mass ‘unknown’.