Limiting Reactants (Reagents)

and Percent Yield

Calculations need to be based on the limiting reactant.

• Example 1: Suppose a box contains 87 bolts, 110 washers and 99 nails. How many sets of 1 bolt, 2 washers and 1 nail can you use to create? What is the limiting factor?

55 sets; washers limit the amount

Calculations need to be based on the limiting reactant.

• Example 2: What is the maximum mass of sulfur dioxide that can be produced by the reaction of 95.6 g carbon disulfide with 100. g oxygen?CS2 + O2 CO2 + SO2

Start by balancing the equation…

Calculations need to be based on the limiting reactant.

• Example 2: What is the maximum mass of sulfur dioxide that can be produced by the reaction of 95.6 g carbon disulfide with 100. g oxygen?CS2 + 3O2 CO2 + 2SO2

Now solve the problem…

Calculations need to be based on the limiting reactant.• Example 2: What is the maximum mass of sulfur dioxide

that can be produced by the reaction of 95.6 g carbon disulfide with 100. g oxygen?CS2 + 3O2 CO2 + 2SO2

2

2

2

2

2

2

22 1611

1.64

1

2

2.76

16.95SOg

SOmol

SOg

CSmol

SOmol

CSg

CSmolCSg

22

2

2

2

2

22 1341

1.64

3

2

0.32

1.100SOg

SOmol

SOg

Omol

SOmol

Og

OmolOg

Which reactant is LIMITING?

Calculations need to be based on the limiting reactant.• Example 2: What is the mass of sulfur dioxide that can

be produced by the reaction of 95.6 g carbon disulfide with 100. g oxygen?CS2 + 3O2 CO2 + 2SO2

2

2

2

2

2

2

22 1611

1.64

1

2

2.76

16.95SOg

SOmol

SOg

CSmol

SOmol

CSg

CSmolCSg

22

2

2

2

2

22 1341

1.64

3

2

0.32

1.100SOg

SOmol

SOg

Omol

SOmol

Og

OmolOg

O2 limits the amount of SO2 that can be produced. CS2 is in excess.

Calculations need to be based on the limiting reactant.• Example 2: What is the mass of sulfur dioxide that can

be produced by the reaction of 95.6 g carbon disulfide with 100. g oxygen?CS2 + 3O2 CO2 + 2SO2

2

2

2

2

2

2

22 1611

1.64

1

2

2.76

16.95SOg

SOmol

SOg

CSmol

SOmol

CSg

CSmolCSg

22

2

2

2

2

22 1341

1.64

3

2

0.32

1.100SOg

SOmol

SOg

Omol

SOmol

Og

OmolOg

134 g of SO2 can be produced in this reaction.

Calculations need to be based on the limiting reactant.

• Example 3: What mass of CO2 could be formed by the reaction of 8.0 g CH4 with 48 g O2?

CH4 + O2 CO2 + H2O

Start by balancing the equation…

Calculations need to be based on the limiting reactant.

• Example 3: What mass of CO2 could be formed by the reaction of 8.0 g CH4 with 48 g O2?

CH4 + 2O2 CO2 + 2H2O

Now solve the problem…

Calculations need to be based on the limiting reactant.• Example 3: What mass of CO2 could be formed by the

reaction of 8.0 g CH4 with 48 g O2?

CH4 + 2O2 CO2 + 2H2O

22

2

4

2

4

44 221

0.44

1

1

0.16

10.8COg

COmol

COg

CHmol

COmol

CHg

CHmolCHg

22

2

2

2

2

22 331

0.44

2

1

0.32

148COg

COmol

COg

Omol

COmol

Og

OmolOg

Which reactant is LIMITING?

Calculations need to be based on the limiting reactant.• Example 3: What mass of CO2 could be formed by the

reaction of 8.0 g CH4 with 48 g O2?

CH4 + 2O2 CO2 + 2H2O

CH4 limits the amount of CO2 that can be produced. O2 is in excess.

22

2

4

2

4

44 221

0.44

1

1

0.16

10.8COg

COmol

COg

CHmol

COmol

CHg

CHmolCHg

22

2

2

2

2

22 331

0.44

2

1

0.32

148COg

COmol

COg

Omol

COmol

Og

OmolOg

Many chemical reactions do not go to completion (reactants are not completely converted to products).

Percent Yield: indicates what percentage of a desired product is obtained.

100yieldltheoretica

yieldalexperimentYield%

• So far, the masses we have calculated from chemical equations were based on the assumption that each reaction occurred 100%.

• The THEORETICAL YIELD is the yield calculated from the balance equation.

• The ACTUAL YIELD is the amount “actually” obtained in an experiment.

• Look back at Example 2. We found that 134 g of SO2 could be formed from the reactants.

• In an experiment, you formed 130 g of SO2. What is your percent yield?

%97100134

130%

g

gYield

Example: A 10.0 g sample of ethanol, C2H5OH, was boiled with excess acetic acid, CH3COOH, to produce 14.8 g of ethyl acetate, CH3COOC2H5. What percent yield of ethyl acetate is this?

CH3COOH + C2H5OH CH3COOC2H5 + H2O

5H

2COOC

3CH mol 1

5H

2COOC

3CH g 88

OH5

H2

C mol 1

5H

2COOC

3CH mol 1

OH5

H2

C 46g

OH5

H2

C mol 1OH5

H2

C 10.0g

5H

2COOC

3CH g1.19

Example: A 10.0 g sample of ethanol, C2H5OH, was boiled with excess acetic acid, CH3COOH, to produce 14.8 g of ethyl acetate, CH3COOC2H5. What percent yield of ethyl acetate is this?

100yieldltheoretica

yieldalexperimentYield%

100g 19.1g 14.8

Yield%

%5.77Yield%