1. Stoichiometry
Chemistry II
Chapter 9

2. Reaction Stoichiometry
Based on conservation of matter
Balanced equation
If the quantity of one substance is known, others can be found
Mole ratios

3. 5 Step Process Construct a balanced equation.
Identify known(s) and unknown(s).
Convert known(s) to moles (if necessary).
Find moles of unknown(s).
Convert unknown(s) into required units (if necessary).

4. Example Problem
How many grams of nitrogen will react with 112 L of hydrogen to form ammonia (NH3)?

5. Step One: Construct a Balanced Chemical Equation
Nitrogen and hydrogen produce ammonia
N H2  NH3
Be honest, did you forget the 2’s?
N H2  2NH3

6. Step Two: Identify Known(s) and Unknown(s)
N H2  2NH3
?g L

7. Step Three: Convert Known to Moles
112L H2 * mol H = ? mol H2
22.4 L H2

8. Step Three: Convert Known(s) to Moles
112L H2 * mol H = L H2
5 mol H2

9. Step Four: Find Moles of Unknown(s)
Convert moles of known to moles of unknown.
Use the mole ratio from the balanced equation.

10. Step Four: Find Moles of Unknown(s)
N H2  2NH3
5 mol H2 * 1 mol N2 = ? Mol N2
3 mol H2

11. Step Four: Find Moles of Unknown(s)
N H2  2NH3
5 mol H2 * 1 mol N2 =
1.67 Mol N2
3 mol H2

12. Step Five: Convert Unknown(s) into Required Units
How many grams of nitrogen?
1.67 Mol N2 * 28 g N2 = ? g N2
1 mol N2

13. Step Five: Convert Unknown(s) into Required Units
How many grams of nitrogen?
1.67 Mol N2 * 28 g N2 =
1 mol N2
46.76 g N2

14. Your Turn….
560 L of oxygen will react with hydrogen to make how many grams of water?

15. One: Construct a Balanced Chemical Equation
Oxygen and hydrogen produce water
O H2  H2O
O H2  2H2O

16. Two: Identify Known(s) and Unknown(s)
O H2  2H2O
560 L ?g

17. Three: Convert Known(s) to Moles
560 L O2 * mol O = 25 mol O2
22.4 L O2

18. Four: Find Moles of Unknown(s)
O H2  2H2O
25 mol O2 * 2 mol H2O = mol O2
50 Mol H2O

19. Five: Convert Unknown(s) into Required Units
50 Mol H2 O * 18 g H2 O = 900 g H2 O
1 mol H2O

20. The End??