1. Stoichiometry

2. Stoichiometry
Stoichiometry: The calculation of quantities of substances involved in chemical reactions.
N2 (g) + 3H2 (g)  2NH3 (g)
The above equation could be read:
1 mol of N2 reacts with 3 moles of H2 to yield 2 moles of ammonia.

3. Stoichiometry Steps 1.) Convert your units to moles
If you follow these steps, you will be an expert at stoichiometry
1.) Convert your units to moles
2.) Use a mole ratio
3.) Convert to the units asked for in the problem

4. Mole-Mole Conversions
2A + B  3C + 7D
Given the number of moles of reactant A (ex. 6 moles A), I can find:
1) The number of moles of reactant B needed to react completely with 6 moles of A (all 6 moles are used up).
2) The number of moles of product C formed.
3) The number of moles of product D formed.

5. Mole-Mole Examples N2 (g) + 3H2 (g)  2NH3 (g)
There is a 1:3:2 mole ratio
If you have 2 moles of N2, how many moles of NH3 will be produced?
If you want 5 moles of product, how many moles of hydrogen gas do you need?
How many moles of nitrogen are needed to react completely with 8 moles of hydrogen?

6. Mole to Mole Example 2 mol N2 2 1 mol NH3 mol N2
N2 + 3H2  2NH3
If you have 2 moles of N2, how many moles of NH3 will be produced?
2 mol N2 2 1
mol NH3
mol N2
2 x 2 / 1 = 4 moles NH3

7. Mole to Mole Example 5 mol NH3 3 2 mol H2 mol NH3
N2 + 3H2  2NH3
If you want 5 moles of product, how many moles of hydrogen gas do you need?
5 mol NH3 3 2
mol H2
mol NH3
5 x 3 / 2 = 7.5 moles H2

8. Mole to Mole Example 8 mol H2 1 mole N2 3 mole H2
N2 + 3H2  2NH3
How many moles of nitrogen are needed to react completely with 8 moles of hydrogen?
8 mol H mole N2
3 mole H2
8 x 1 / 3 = 2.67 mole N2

9. Practice
2H2O2 -> 2H2 + O2
If you have 10 moles of H2, how many moles of H2O2 did you originally have?
If you started out with 3.5 moles of H2O2, how many moles of O2 did you create?

10. Reaction Conversions
****The only way to convert from one compound to something totally different in the reaction is to use the MOLE TO MOLE RATIO from the coefficients!!!****

11. Reaction Conversions 22.4 L at STP 1 mole
Note – If you don’t have moles already, your first step is to convert to moles!
Mole Review:
Molar Mass
6.02 x 1023 particles
22.4 L at STP
1 mole

12. C. Molar Volume at STP (22.4 L/mol) (g/mol) particles/mol LITERS
OF GAS
AT STP
Molar Volume
(22.4 L/mol)
MASS IN
GRAMS
MOLES
NUMBER OF
PARTICLES
Molar Mass
(g/mol)
6.02  1023
particles/mol
Molarity (mol/L)
LITERS OF
SOLUTION

13. Volume-Volume Conversions
How many liters of oxygen are required to burn 3.86 L of carbon monoxide? CO (g) + O2 (g)  2CO2 (g)
How many liters of PH3 are formed when L of hydrogen reacts with phosphorus? P4 (s) + 6 H2 (g)  4 PH3 (g)

14. Practice
Find the liters of sugar required to produce 1.82L of carbon dioxide gas at STP from the reaction described by the following equation:
C6H12O6 -> 2C2H6O + 2CO2

15. Mass-Mass Conversions
N2 (g) + 3H2 (g)  2NH3 (g)
How many grams of hydrogen gas are required for 3.75 g of nitrogen gas to react completely?
What mass of ammonia is formed when g of nitrogen gas react with hydrogen gas?

16. More Mass-Mass Conversions
N2 + 3H2  2NH3
How many grams of H2 are required to produce 5.0 grams of NH3?
Grams NH3  moles NH3  moles H2  grams H2
5.0 g NH mole NH mole H g H2
17 g NH mole NH3 1 mole H2
5.0 x 3 x 2 / 17 / 2 = 0.88 g H2

17. More Practice*
The combustion of propane, C3H8, a fuel used in backyard grills and camp stoves, produces carbon dioxide and water vapor C3H8 (g) + 5O2 (g)  3CO2 (g) + 4H2O (g) What mass of carbon dioxide forms when 95.6 g of propane burns?
Solid xenon hexafluoride is prepared by allowing xenon gas and fluorine gas to react Xe (g) + 3F2 (g)  XeF6 (s)
How many grams of fluorine are required to produce 10.0 g of XeF6?
How many grams of xenon are required to produce 10.0 g of XeF6?

18. Mixed Practice - Examples
How moles of CO2 are produced when 52.0 g C2H2 burns? C2H2 (g) + 5O2 (g)  4CO2 (g) + 2H2O (g)
How many liters of hydrogen gas are formed from 50 grams of potassium? K (s) + 2H2O (l)  2KOH (aq) + H2 (g)

19. Mixed Practice
How many molecules of oxygen are produced by the decomposition of 6.54 g of potassium chlorate (KClO3)? KClO3 (s)  2KCl (s) + 3O2 (g)
How many grams of nitrogen dioxide must react with water to produce 5.00 x 1022 molecules of nitrogen monoxide? NO2 (g) + H2O (l)  2HNO3 (aq) + NO (g)

20. Limiting Reagent
Limiting Reagent: The reactant that limits the amount of product that can be formed in a reaction.
The reaction will stop when all of this reactant is used up.
Determines the amount of product that is produced.
Excess Reagent: You have more than you need of this reactant.
The reaction will stop before all of this reactant is used up. You will have some of this reactant leftover.

21. Everyday Example You have :
1 loaf of bread (containing 14 slices of bread)
4 jars of peanut butter
2 jars of jelly
A) How many peanut butter and jelly sandwiches can you make?
B) What is the limiting reagent?
C) What are the reactants in excess?

22. Limiting Reactants
**The amount of product that can be formed in a reaction is always determined by the limiting reactant!!**

23. S’mores A s’mores MUST have: If you had: 2 graham crackers
2 pieces of chocolate
1 marshmallow
If you had:
8 graham crackers
4 pieces of chocolate
6 marshmallows
How many s’mores could you make?

24. Limiting Reagent Example Problems
1) If 2.70 mol C2H4 is reacted with 6.30 mol O2, what is the limiting reagent? C2H4 (g) + 3O2 (g)  2CO2 (g) + 2H2O (g)

25. (cont’d)
2) Identify the limiting reagent when 6.00 g HCl reacts with 5.00 g Mg Mg (s) + 2HCl (aq)  MgCl2 (aq) + H2 (g)
- How many grams of MgCl2 are produced in this reaction? __________________
Which reactant is in excess? _________________
How much of your excess reagent do you have leftover? _____________________

26. (cont’d)*
3) How many grams of water can be produced by the reaction of 2.40 mol C2H2 with 7.4 mol O2? C2H4 (g) + 3O2 (g)  2CO2 (g) + 2H2O (g) Limiting Reagent? ______________ Excess Reagent? _______________

27. Percent Yield Percent Yield = Actual Yield x 100% Theoretical Yield
Theoretical Yield: the maximum amount of product that could be formed from the given amounts of reactants (ideal conditions).
Calculated using stoichiometry.
Actual Yield: the amount of product that actually forms in a lab.
Actual yield is usually less than theoretical yield.
Percent Yield = Actual Yield x 100%
Theoretical Yield

28. Percent Yield Example Problem
If 3.75 g of nitrogen completely react, what is the theoretical yield of NH3?
N2 (g) + 3H2 (g)  2NH3 (g)
If the actual yield is 3.86 g, what is the percent yield?

29. Practice
Find the percent yield if 84.8 g of iron (III) oxide reacts with an excess of carbon monoxide to produce 55.0 g of iron Fe2O3 (s) + 3CO (g)  2Fe (s) + 3CO2 (g)