You calculate yielding, specifically percent yield, by dividing the actual yield (the amount of product you actually obtain from a reaction) by the theoretical yield (the amount of product you should obtain based on stoichiometry) and then multiplying by 100%.
Here's a breakdown:
Understanding the Terms
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Actual Yield: The experimentally obtained amount of product after carrying out a chemical reaction. This is what you actually weighed out in the lab.
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Theoretical Yield: The maximum amount of product that could be formed in a chemical reaction based on the complete consumption of the limiting reactant and the stoichiometry of the balanced chemical equation. This is what you calculate.
The Formula
The percent yield is calculated using the following formula:
Percent Yield = (Actual Yield / Theoretical Yield) * 100%Steps to Calculate Percent Yield:
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Write a balanced chemical equation: This is crucial for determining the stoichiometric relationships between reactants and products.
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Determine the limiting reactant: Identify which reactant will be completely consumed first, thus limiting the amount of product that can be formed.
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Calculate the theoretical yield: Based on the limiting reactant and the balanced chemical equation, calculate the maximum amount of product (in grams or moles) that can be produced. This is your theoretical yield.
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Measure the actual yield: After performing the experiment, carefully measure the actual amount of product obtained.
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Calculate the percent yield: Plug the actual yield and theoretical yield into the formula above and calculate the percentage.
Example:
Let's say you perform a reaction where the theoretical yield of a product is 10.0 grams. However, after performing the experiment and isolating the product, you only obtain 8.0 grams.
- Actual Yield = 8.0 grams
- Theoretical Yield = 10.0 grams
Percent Yield = (8.0 grams / 10.0 grams) * 100% = 80%
Therefore, the percent yield of this reaction is 80%.
Factors Affecting Yield
Several factors can cause the actual yield to be less than the theoretical yield:
- Incomplete Reactions: Not all reactants may convert to products.
- Side Reactions: Other reactions may occur, consuming reactants and forming unwanted products.
- Loss of Product: Some product may be lost during transfer, purification, or other experimental procedures.
- Impure Reactants: Reactants may not be 100% pure, leading to lower product formation.
Significance of Percent Yield
The percent yield provides insight into the efficiency of a chemical reaction and experimental technique. A higher percent yield indicates a more efficient reaction and fewer losses during the experimental process.
