1. Stoichiometry
Stoichiometry is a method used in chemistry to determine the amount of materials used and produced in a chemical reaction. It is a vital part of all quantitative chemistry. Learn well.

2. Step by Step Example Problem
What mass of aluminum will be produced if excess aluminum chloride is reacted with 11.23g of magnesium?
The word excess indicates that there will be more aluminum chloride than you will need.

3. Step #1 – Predict the Products
What are the two products when aluminum chloride reacts with magnesium?
Magnesium chloride and aluminum.

4. Step #2 – Write Proper Formulas
It is important to write the proper formulas using subscripts. On your worksheet, write the formulas for aluminum chloride reacting with magnesium to form magnesium chloride and aluminum.
AlCl3 + Mg  MgCl2 + Al

5. Step #3 – Write Balanced Equation
AlCl3 + Mg  MgCl2 + Al
Balance the equation on your worksheet.
2AlCl3 + 3Mg  3MgCl2 + 2Al

6. Step #4 – Write down your given
You are given are 11.23g of magnesium, it is important that you write it all down; the number, the units and the substance.
11.23g Mg

7. Step #5 – Convert grams to moles
You are given are 11.23g of magnesium, convert this to moles of magnesium. Use factor label.
11.23g Mg moles Mg

8. Step #5 – Convert grams to moles
11.23g Mg 1 mole Mg moles Mg
24.3g Mg

9. Step #6 – Moles to Moles
This is Stoichiometry!!! Typically you should just continue on with the problem from step #5, but since we are breaking them up, start this step by writing down what you calculated in step #5.
0.462 moles Mg
Now use factor label to convert to moles of Al.
(remember to use your balanced equation)

10. Step #6 – Stoichiometry 0.462 moles Mg 2 moles Al 0.308 moles Al

11. Step #7 – Convert moles to grams
0.308 moles Al g Al g Al
1 mole Al
So we have determined that if 11.23g of magnesium reacts with excess aluminum chloride, it will produce 8.32g of aluminum.

12. Practice Problem #1
Do this practice problem and show all of your work on your worksheet. When you finish, go to the next screen to check your answer.
How many grams of product will be produced from the composition of 34.21g of aluminum with excess chlorine?

13. 2Al + 3Cl2  2AlCl3

14. Practice Problem #2
Do this practice problem and show all of your work on your worksheet. When you finish, go to the next screen to check your answer.
How many grams of sodium will react with g of magnesium chloride?
Notice that this problem wants to know the amount of the other reactant. No worries, it is done the same way as the other stoichiometry problems.

15. 2Na + MgCl2  2NaCl + Mg

16. Practice Problem #3
If you decompose 1.25 moles of aluminum oxide, how many grams of aluminum can you produce?
Notice this problem does NOT start with grams, therefore you can skip step #5. Show all your work on your worksheet and then go to the next frame to check your answer.

17. 2Al2O3  4Al + 3O2