Lecture on Reaction Yields

Learning Objectives

• Explain the concepts of theoretical yield and limiting reagents
• Derive the theoretical yield for a reaction under specified conditions
• Calculate the percent yield for a given reaction

Key Concepts

Theoretical Yield

• The amount of product predicted by stoichiometry from the complete use of the limiting reagent.
• It assumes all of the limiting reagent is consumed in the reaction.
• Actual Yield: The actual amount of product obtained from a reaction, often less than the theoretical yield due to:
  • Competing side reactions
  • Incomplete reactions
  • Difficulty in product recovery

Percent Yield

• Expresses the efficiency of a reaction.

• Calculated as:

  [ \text{Percent Yield} = \left( \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \right) \times 100% ]

• Requires that the actual yield and theoretical yield are in the same units.

Example Problem

1. Given:

   • Copper metal obtained = 0.392 g (Actual Yield)
   • Reaction involved copper sulfate and excess zinc metal.
   • Copper sulfate is the limiting reagent.

2. Calculate Theoretical Yield:

   • Copper sulfate given = 1.1274 g
   • Convert grams of copper sulfate to moles (using stoichiometric factor)
   • Convert moles of copper to grams using molar mass of copper:
     • Molar mass of Copper = 63.55 g/mol
   • Theoretical Yield of Copper = 0.507 g

3. Calculate Percent Yield:

   • Using formula:

     [ \text{Percent Yield} = \left( \frac{0.392 \text{ g (Actual Yield)}}{0.507 \text{ g (Theoretical Yield)}} \right) \times 100% ]

   • Result = 77.3%

   • Interpretation: 77.3% of the theoretical yield was recovered in the reaction.

Conclusion

• Understanding the concepts of limiting reagents and yields is crucial in predicting and evaluating the efficiency of chemical reactions.