What You Will Learn
Theoretical, Actual & Percent Yield
Why Is It Important?
Actual results are more important than theoretical.
Final Exam
Theoretical, Actual & Percent Yield
Theoretical yield
The theoretical yield of a reaction is the amount of product that
would be formed if the reaction went to completion.
Actual yield
Amount of a specified pure product actually obtained from a given
reaction.
Calculating Percent Yield
Stoichiometry
The left side and right side of the chemical reaction must
have equal amounts of each element.
We fix the problem by adding prefixes or coefficients.
Stoichiometry
After adding prefixes to the O2 and the H2O count the
atoms on the left and right again. Are they equal now?
Practice Calculating Theoretical Yield
Determine the theoretical yield of hydrogen gas (H2) in
grams for each of the following chemical reactions.
1. Zn + 2 HCl → ZnCl2 + H2
2. 2 H2O → 2 H2 + O2
3. Mg + 2 H2O → Mg(OH)2 + H2
Practice Calculating Percent Yield
Determine the percent yield for the following reactions if the
actual yield of hydrogen gas (H2) is 1 gram.
1. Zn + 2 HCl → ZnCl2 + H2
2. 2 H2O → 2 H2 + O2
3. Mg + 2 H2O → Mg(OH)2 + H2
Bell-Ringer: Theoretical Yield
If your cell phone comes out you get a zero. Work alone & quietly.
Open notebook – Part 1 of 4 (10 Minutes)
Answer in your bell-ringer notebook in complete sentences.
Determine the grams needed for each theoretical reaction.
Example:
2MgO
80.6 grams

2Mg
48.6 grams
+
O2
32.0 grams
Note the total mass before and after the reaction.
1. 8 Fe + S8 → 8 FeS
2. Zn + 2 HCl → ZnCl2 + H2
3. 2 H2O → 2 H2 + O2
4. HCl + NaOH  H2O + NaCl
Excess & Limiting Reactants
What are the excess reactants?
What are the limiting reactants?
For limiting and excess we are talking about reactants.
Bell-Ringer: Limiting Reagent
If your cell phone comes out you get a zero. Work alone & quietly.
Open notebook – Part 2 of 4 (10 Minutes)
Answer in your bell-ringer notebook in complete sentences.
Determine the limiting reagent in the following reactions.
5.
2C2H2 + 5O2  4CO2 + 2H2O
Theoretical: _______
Actual:
52 grams
6.
_________
150 grams
HCl + NaOH  H2O + NaCl
Theoretical: _______
Actual:
33.5 grams
7.
Zn
_________
40 grams
+ 2 HCl → ZnCl2 + H2
Theoretical: _______
Actual:
65 grams
8.
8 Fe
Theoretical: _______
Actual:
448 grams
_________
70 grams
+
S8
→ 8 FeS
_________
251 grams
Theoretical Yield
For yield we are talking about products.
Bell-Ringer: Percent Yield
If your cell phone comes out you get a zero. Work alone & quietly.
Open notebook – Part 3 of 4 (5 Minutes)
Answer in your bell-ringer notebook.
Determine the theoretical yield for each product.
9. 2C2H2 + 5O2  4CO2 + 2H2O
10. HCl + NaOH  H2O + NaCl
Bell-Ringer: Percent Yield
If your cell phone comes out you get a zero. Work alone & quietly.
Open notebook – Part 4 of 4 (5 Minutes)
Answer in your bell-ringer notebook.
Determine the percent yield for the given actual yield.
11. 2C2H2 + 5O2  4CO2 +
160 grams
12. HCl + NaOH  H2O
15.5 grams
2H2O
34 grams
+
NaCl
45 grams
Estimating Percent Yield
Consider the following theoretical yield:
Estimating Percent Yield
Can we estimate how much product was actually made?
Estimating Percent Yield
Can we estimate how much product was actually made?
A. 5%
B. 10%
C. 50%
D. 100%
Estimating Percent Yield
Consider the following theoretical yield:
Estimating Percent Yield
Can we estimate how much product was actually made?
Estimating Percent Yield
Can we estimate how much product was actually made?
A. 10%
B. 30%
C. 90%
D. 100%
Chemistry Humor or College Reality?
Practical:
MgSO4 + H2O  MgSO4(aq)
Working in pairs:
1. Record the weight of two plastic cups, one at a time.
2. Weigh approximately 10 grams of epsom salt into one plastic cup
& record the exact grams.
3. Weigh approximately 50 grams of water into a different plastic
cup & record the exact grams.
4. Calculate from this data what your theoretical yield of saltwater
should be.
5. Now, make saltwater by repeatedly combining (pouring) the
water and salt back and forth at least 10 times.
6. Weigh the finished product of saltwater & record the exact grams.
7. Calculate your percent yield of saltwater.
Practical:
Results:
1st
MgSO4 + H2O  MgSO4(aq)
Practical:
Results:
2nd
MgSO4 + H2O  MgSO4(aq)
Practical:
Results:
4th
MgSO4 + H2O  MgSO4(aq)
Practical:
Extra Credit
After calculating the percent yield for your reaction, then calculate
how many moles of MgSO4 were used in the following reaction…
MgSO4 + H2O  MgSO4(aq)
50 grams
50 grams of MgSO4 is equal to how many moles of MgSO4?
Exit-Ticket: Percent Yield
If your cell phone comes out you get a zero. Work alone & quietly.
Open notebook – Part 1 of 1 (10 Minutes)
Answer in your bell-ringer notebook in complete sentences.
Calculate the percent yield for the following reactions.
1. 2C2H2 + 5O2 
4CO2 +
Theoretical: _______
Actual:
100 grams
2. HCl
+ NaOH 
+ 2 HCl →
+
S8
_________
30 grams
ZnCl2 +
Theoretical: _______
Actual:
100 grams
4. 8 Fe
_________
15 grams
H2O + NaCl
Theoretical: _______
Actual:
13 grams
3. Zn
2H2O
→ 8 FeS
Theoretical: _______
Actual:
500 grams
H2
_________
2 grams