1. Percentage Yield
and Energy
Lesson 3

2. Sometimes reactions do not go to completion
Sometimes reactions do not go to completion. Reaction can have yields from 1% to 100%.
1. How many grams of Fe are produced by the reaction of 100. g of Fe2O3, if the percentage yield is 75.0%? 2
Fe2O C  Fe CO2 4
100. g
? g
100. g Fe2O3
x 1 mole
x 4 mole Fe
x g x
= g
159.6 g
2 mole Fe2O3
1 mole

3. Percentage Yield = Actual Yield x 100%
Theoretical Yield
Actual Yield is what is experimentally measured.
Theoretical Yield is what is calculated using stoichiometry.

4. 2. In an experiment 152. g of AgNO3 is used to make 75. 1 g of
2. In an experiment 152. g of AgNO3 is used to make 75.1 g of Ag2SO4(s). Calculate the percentage yield.
AgNO3(aq) + Na2SO4(aq)  Ag2SO4(s) + 2NaNO3(aq)
75.1 g actual yield 2 1
152 g
? g
152. g AgNO3
x 1 mole
x 1 Ag2SO4
x g
= g
169.9 g
2 mole AgNO3
1 mole
% yield =
x %
= 53.8 %
139.5

5. Energy Calculations
The energy term in a balanced equation can be used to calculate the amount of energy consumed or produced in a reaction.
How much energy is required to produce 25.4 g of H2?
+ 2H2O  H2 + O2
213 kJ 2
? kJ
25.4 g
25.4 g H2
x 1 mole
x kJ
= kJ
2.02 g
2 mole H2

6. 4. How many molecules of H2 can be produced when 452 kJ of
4. How many molecules of H2 can be produced when 452 kJ of energy if consumed?
2 H2O
213 kJ  2
H2 + O2
452 kJ
? Molecules
452 kJ
x 2 moles H2
x x molecs
= x molecs
213 kJ
1 mole

7. 5. How much energy is produced by an explosion of a 5. 2 L
5. How much energy is produced by an explosion of a 5.2 L balloon full of hydrogen at STP?
H2 + O2  2H2O 2
213 kJ
5.2 L
? kJ
5.2 L
x 1 mole
x kJ
= kJ
22.4 L
2 moles H2