33. Percentage Yield: Theoretical & Actual Yield

1. Key Terms

  • Yield: The amount of product obtained from a chemical reaction (measured in grams or moles).

  • Theoretical Yield: The maximum amount of product you expect to get based on balanced equation calculations.

  • Actual Yield: The amount of product you actually get when you carry out the reaction in real life.

2. Why is the Actual Yield usually lower?

There are three common reasons why you rarely get 100% of the theoretical yield:

  1. Incomplete Reactions: Not all reactants react to form products. This happens if the reaction is very slow or if it is a reversible reaction that reaches equilibrium (where products break back down into reactants).

  2. Side Reactions: Reactants may react in unexpected ways to produce different products. For example, nitrogen might react with oxygen from the air to form nitrogen dioxide instead of the intended ammonia.

  3. Loss During the Process: Product can be lost when transferring between containers.

    • Gases can float away and escape.

    • Liquids or solids get left behind on filter paper, in beakers, or on glass rods during filtration.

3. Percentage Yield Calculation

The percentage yield tells you how successful the reaction was as a percentage of the maximum possible.

Percentage Yield = (Actual Yield / Theoretical Yield) × 100

  • Example Calculation:

    • Theoretical Yield (predicted): 18g

    • Actual Yield (obtained): 15g

    • Calculation: (15 / 18) × 100 = 83.3%

  • Range: A percentage yield can range from 0% (no product made) to 100% (all predicted product made).

4. Importance in Industry

Industrial processes aim for a high percentage yield to:

  • Reduce waste.

  • Keep costs down.

  • Make the process more sustainable and profitable.