1. Section 2: Stoichiometric Calculations
A car’s air bags are powered by the rapid reaction of a small mass of sodium azide (Na3N) into a large volume of N2 gas.
(all in less than a second)
You will use a balanced
chemical equation
to calculate the amount
of reactant needed or
product formed.
Print 1-8,10-13

2. Stoichiometric Calculations
In a typical stoichiometric problem,
1) Convert grams of given to moles of given
2) Use the mol ratio to convert moles of given to moles of wanted
3) Convert moles of wanted to grams of wanted
Note – you can start or stop a stoichiometry problem anywhere on the above path, depending on the question.

3. Mg + 2 HCl → MgCl2 + H2 mol ratio Moles to Moles
How many moles of HCl are required to produce 5.5 mol MgCl2?
Mg HCl → MgCl2 + H2
2 mol HCl
1 mol MgCl2
5.5 mol MgCl2 x =
11 mol HCl
mol ratio 3

4. Mg + 2 HCl → MgCl2 + H2 mol ratio molar mass Moles to Grams
How many grams of H2 are produced from 4.0 mol HCl?
Mg HCl → MgCl2 + H2
1 mol H2
2 mol HCl
2.02 g H2
1 mol H2
4.0 mol HCl x x =
4.04 g H2
mol ratio
molar mass 4

5. Mg + 2 HCl → MgCl2 + H2 molar mass mol ratio Grams to Moles
How many mol of H2 are produced from
48 g Mg?
Mg HCl → MgCl2 + H2
1 mol Mg
24.31 g Mg
1 mol H2
1 mol Mg
48 g Mg x x =
1.97 mol H2
molar mass
mol ratio 5

6. Mg + 2 HCl → MgCl2 + H2 mol ratio molar mass molar mass Grams to Grams
How many grams of H2 are produced from
18 g HCl?
Mg HCl → MgCl2 + H2
1 mol HCl
36.46 g HCl
1 mol H2
2 mol HCl
2.02 g H2
1 mol H2
18 g HCl x x x =
0.499 g H2
mol ratio
molar mass
molar mass 6

7. Have we learned it yet?
Try these on your own 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 grams of NO can be made from 47 g of NH3?

8. Answers 4 NH3 + 5 O2  6 H2O + 4 NO 2.4 mol H2O 13 g NH3 83 g NOb) c)
6 mol H2O
4 mol NH3 x
2.4 mol H2O =
1.6 mol NH3
4 mol NH3
4 mol NO x
17.04 g NH3
1 mol NH3 x
13 g NH3 =
0.75 mol NO
1 mol NH3
17.04 g NH3 x
4 mol NO
4 mol NH3 x
30.01 g NO
1 mol NO x
47 g NH3
83 g NO =