1. Limiting Reactants & Percent Yield
Section 12.3

2. If we have… how many sets can we make?
Limiting reactant = the reactant that runs out first causing the reaction to stop
Excess reactant = reactant that does not get completely used up during a reaction
With this left over
Excess

3. Steps to solve limiting reactants problems
Split into 2 problems
Solve each problem
Pick smallest answer
Smallest answer comes from limiting reactant
Largest answer comes from excess reactant

4. Calculating product when reactant is limiting
If we had 12 moles of nitrogen and 18 moles of hydrogen, what is the maximum number of moles of NH3 that could be produced?
N2 + 3H2  2 NH3

5. Calculating product when reactant is limiting
If we had 112 grams of nitrogen and 18 grams of hydrogen, what is the maximum number of grams of NH3 that could be produced?
N2 + 3H2  2 NH3
2(14) (1)
Remember…
Nitrogen
Hydrogen
Pick lowest number
Therefore Hydrogen is your limiting reactant

6. Calculating product when reactant is limiting
With 48 grams of magnesium and 48 grams of oxygen available, how much product can be formed?
2Mg + O2  2 MgO
(16)
Oxygen
Magnesium
Pick lowest number
Therefore Magnesium is your limiting reactant and oxygen is the excess reactant

7. Limiting Reactants Practice III
How many grams of sodium chloride can be produced in the following reaction with 150 grams of sodium and 200 grams of chlorine?
2Na + Cl2  2 NaCl
(35.5)
Sodium
Chlorine
Pick lowest number

8. Limiting Reactants Practice III
In the above reaction, how many more grams of chlorine will be required to fully react with the remaining sodium?
We need to figure out how many grams of chlorine is needed to react with 150 grams of sodium
2Na + Cl2  2 NaCl
(35.5)
Sodium
Chlorine needed = 231 g
Chlorine given (from problem) = 200 g
Additional Chlorine needed = 31 g

9. Percent Yield
Actual yield = the actual amount of product formed during an experiment
Theoretical yield = amount of product that could be produced according to calculations
Percent yield = ratio of actual and theoretical yield

10. Percent Yield Practice I
A student uses stoichiometry to calculate the predicted yield of CO2 in a chemical reaction as 323 g. When the student mixes the chemicals to make the CO2, he finds that the reaction only produces 308 g of CO2. What is the percent yield?

11. In the reaction, how many grams of potassium oxide can be produced with 78 grams of potassium and 140 grams of boron oxide?
6 K + B2O3  3 K2O + 2 B
(10.8)+3(16) 2(39.1)+16
Potassium
Boron Oxide
Pick lower number

12. Problem 2 continued
If the actual yield from the above reaction was 81 grams, what is the percent yield?
Actual yield = 81 grams
Theoretical yield = g (from last slide)

13. Pick lower number N2 + 3H2  2 NH3
3. The actual yield in the above reaction was 39 grams of ammonium. Using 84 grams of nitrogen and 8 grams of hydrogen, what is the percent yield?
-first we must calculate the theoretical yield of product which means we need to find our limiting reactant
N2 + 3H2  2 NH3
2(14) (1)
Nitrogen
Hydrogen
Pick lower number

14. Problem 3 continued
Actual yield = 39 grams
Theoretical yield = 45.3 g (from last slide)