1. Stoichiometry
Chemistry
Ms. Piela

2. Stoichiometry
The quantitative study of reactants and products in a chemical reaction
Chemical reactions give info about how molecules combine, and can be used to determine amounts of substances that form

3. Mole to Mole Calculations
When using a chemical equation to determine the amount of the substance, you must relate them by their mole ratios
Example #1:
____ H2 + ____ O2 → ____ H2O
If you start with 4 moles of O2 how many moles of H2O would form?

4. Mole to Mole Calculations
Example #2:
___ Fe + ____ S → ___Fe2S3
How many moles of iron (III) sulfide, Fe2S3, forms if the reaction initially starts with 8 moles of iron, Fe?

5. Mass to Mass Calculations
Example #1:
___ H2 + ___ O2 → ___ H2O
If 2.4 g of O2 are reacted with excess H2 gas, how many moles of H2O would form?
0.15 mol H2O

6. Mass to Mass Calculations
Example #2:
___ H2 + ___ O2 → ___ H2O
In the above equation, if I started with 3 grams of H2, how many grams of H2O would form?
26.8 g H2O

7. Mass to Mass Calculations
Example #3:
_ NH3 (g) + _ CO2 (g) → _ (NH2)2CO(aq) + _H2O(l)
When 2.00 grams of ammonia, NH3, react with excess CO2, what mass of water (in grams) is formed?
1.06 g H2O

8. Limiting Reactant The reactant used up first in a chemical reaction
Also called limiting reagent
After a reaction, excess reactants are left
These are reactants present in greater quantities that remain after a reaction takes place

9. 4 legs + 1 seat + 10 screws → 1 chair
Limiting Reactant
Chair analogy:
It’s your lucky day! Mr. Nelson has hired you to make chairs! The chairs follow the “reaction”:
4 legs + 1 seat + 10 screws → 1 chair
Here are the supplies you have: 10 legs, 5 seats, and 100 screws. How many chairs be made? What is the limiting reactant?

10. Limiting Reactant Simulation
nts-products-and-leftovers

11. Limiting Reactant
The limiting reactant can be found by determining which of the starting amounts yields the least amount of product

12. Limiting Reactant Example Problem
Sodium chloride can be prepared by the reaction of sodium with chlorine gas:
2Na (s) + Cl2 (g) ® 2NaCl (s)
Suppose that 6.70 mol Na reacts with 3.2 mol Cl2
How many moles of NaCl will be formed in this reaction?
What is the limiting reactant? Cl2
6.4 mol NaCl

13. Limiting Reactant Practice Problem
2.70 mol C2H4 is reacted with 6.30 mol of O2. Calculate the amount in moles of water that forms, and identify the limiting reactant.
C2H4 (g) + 3O2 (g) ® 2CO2 (g) + 2H2O (g)
4.2 mol H2O

14. Limiting Reactant Example Problem
Urea is prepared by reacting ammonia with carbon dioxide:
2 NH3 (g) + CO2 (g) → (NH2)2CO(aq) + H2O(l)
In one process, g of NH3 are treated with 1142 g of CO2. Calculate the mass of urea, (NH2)2CO, formed.
1122 g urea

15. Limiting Reactant Practice Problem
Calculate the number of grams of NH3 produced by the reaction of 5.40 g of hydrogen with 8.25 g of nitrogen. The balanced equation is:
N2 + 3 H2 ® 2 NH3
9.97 g NH3

16. Percent Yield
Theoretical yield is the amount of product that would result if all the limiting reagent reacted
Actual yield is the amount actually obtained in lab from a reaction
Actual yield is almost always less than theoretical

17. Percent Yield
Percent yield describes proportion of actual yield to theoretical yield.

18. Percent Yield Example Problem
When 84.8 g of iron (III) oxide reacts with an excess of carbon monoxide, 54.3 g of iron is produced. What is the percent yield of this reaction?
Fe2O3 (s) + 3CO (g) ® 2 Fe (s) + 3CO2 (g)
91.6%

19. Percent Yield Practice Problem
If 25 grams of carbon dioxide gas can be produced in the following reaction, how many grams of sodium hydroxide should be produced? If 10.7 grams of sodium hydroxide are actually produced, what is the percent yield?
NaHCO3 ® NaOH + CO2
22.7 g NaOH / 41.1%