Percentage Yield

Definition of Percentage Yield

Percentage yield compares the amount of product actually made in a chemical reaction to the maximum amount that could be made (theoretical yield).

Actual yield is the mass of product you collect from the experiment or industrial process.

Theoretical yield is the maximum mass of product expected based on calculations from the balanced chemical equation (see separate notes on Theoretical Yield for detailed explanation).

The formula for percentage yield is:

$$\text{Percentage yield} = \left( \frac{\text{Actual yield}}{\text{Theoretical yield}} \right) \times 100$$

This value is always expressed as a percentage (%) and shows how efficient the reaction was in producing the desired product. Note that percentage yield can never be more than 100% because you cannot get more product than the theoretical maximum.

Calculating Percentage Yield

To calculate percentage yield, follow these steps:

• Measure the actual mass of the product obtained after the reaction.
• Calculate the theoretical mass of product expected from the balanced chemical equation (using relative formula masses and mole ratios; see other notes for details).
• Use the percentage yield formula to find the efficiency of the reaction.

For instance, if a reaction should produce 10.0 g of product but only 7.5 g is collected, the percentage yield is:

$$\text{Percentage yield} = \left( \frac{7.5}{10.0} \right) \times 100 = 75\%$$

Factors Affecting Percentage Yield

Several factors can cause the actual yield to be less than the theoretical yield, reducing the percentage yield:

• Incomplete reactions: Sometimes the reaction does not go to completion, so not all reactants are converted into products.
• Loss during product recovery: Some product may be lost during processes like filtration, transfer, or purification.
• Side reactions: Reactants may react in other ways, producing unwanted by-products instead of the desired product.

These factors are common in both laboratory and industrial settings and affect how much product can be collected.

Importance of Percentage Yield

Percentage yield is important because it helps chemists and industries:

• Assess efficiency: It shows how well a reaction produces the desired product.
• Save money: Higher yields mean less waste and better use of expensive reactants.
• Reduce environmental impact: Less waste and fewer by-products mean less pollution and lower disposal costs.
• Compare methods: It allows comparison between different experimental or industrial processes to find the most effective one.

For example, an industrial process with a low percentage yield might be improved to increase profit and reduce waste.