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Calculating Reaction Yields

4.4 Reaction Yields

Background: Theory vs. Reality

In chemistry, we distinguish between what "should" happen on paper and what "actually" happens in the laboratory:

  • Theoretical Yield: The maximum amount of product that can be produced based on stoichiometry. This is the "perfect world" number you calculate using balanced equations.
  • Actual Yield: The amount of product you physically weigh on a scale after the reaction is finished. It is almost always lower than the theoretical yield due to spills, side reactions, or incomplete mixing.
  • Percent Yield: A measure of efficiency, calculated as:
    (Actual Yield / Theoretical Yield) × 100%

✏️ Integrated Practice

A chemist is reacting Calcium with Chlorine to produce Calcium Chloride (CaCl2), a common electrolyte supplement.

Step 1 (Part A): Determining the Theoretical Yield
The chemist starts with enough Calcium to produce exactly 45.0 g of CaCl2 based on their pencil-and-paper calculations.
Question: What is this 45.0 g value called?

Click for Part A Answer

This is the Theoretical Yield.

Step 2 (Part B): Calculating Clinical Efficiency
The chemist performs the reaction in the lab. After drying and weighing the final product, they only collect 39.6 g of CaCl2.
Question: Using the value from Part A, calculate the Percent Yield.

Click for Part B Answer

Percent Yield = (Actual / Theoretical) × 100
Percent Yield = (39.6 g / 45.0 g) × 100 = 88.0%