Lecture Notes: Yield in Chemical Reactions

Key Concepts

• Yield: The amount of product obtained from a chemical reaction.
  • Actual Yield: The amount actually obtained from the reaction.
  • Theoretical Yield: The amount expected based on stoichiometric calculations.
• Measurement: Yield can be measured in grams or moles.

Example Calculation

• Reaction Example: 2 grams of hydrogen react with 16 grams of oxygen.
  • Theoretical Yield: 18 grams of water (2 + 16 = 18).
  • Actual Yield Example: 15 grams of water.

Reasons for Discrepancy in Yield

1. Incomplete Reactions

   • Reactants might not fully react, leaving some unreacted.
   • Reasons include:
     • Slow reaction rate.
     • Reversible reactions reaching equilibrium (e.g., nitrogen and hydrogen forming ammonia).

2. Side Reactions

   • Reactants form different products than expected.
   • Example: Nitrogen reacts with oxygen to form nitrogen dioxide instead of ammonia.

3. Loss of Products

   • Physical loss during the process.
   • Examples:
     • Gaseous products escaping.
     • Incomplete capture during filtration.

Filtration Example

• Challenges:
  • Liquid left in the beaker, on the solid, or on filter paper.
  • Solid loss when scraping off filter paper.

Calculating Percentage Yield

• Formula:

  • [ \text{Percentage Yield} = \left( \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \right) \times 100 %
  • Range: 0% (no product) to 100% (all expected product obtained).

• Example Calculation:

  • Actual Yield: 15 grams.
  • Theoretical Yield: 18 grams.
  • Percentage Yield: ( \frac{15}{18} \times 100 = 83.3% ).

Conclusion

• The video covers the concept of yield, reasons for yield discrepancies, and how to calculate percentage yield.
• Aim: Understand why actual yield might differ from theoretical yield and how to quantify it.