Percentage Yield

Definition and Formula

Percentage yield is a concept used in chemistry to measure the efficiency of a chemical reaction.
It compares the actual yield (the amount actually produced) with the theoretical yield (the maximum possible amount that could be produced).
The formula to calculate percentage yield is: (Actual yield / Theoretical yield) * 100

Ideal Conditions and Limiting Factors

The theoretical yield assumes that the reaction proceeds under ideal conditions with no loss of materials, which is rarely the case.
The actual yield is usually less than the theoretical yield because of factors such as incomplete reactions, loss of product during transfer, side reactions, or impurities in the reactants.

Implications of Percentage Yield

A high percentage yield indicates a more successful reaction that efficiently converts reactants to products, which is particularly important in industrial processes.
On the other hand, a low yield may suggest that the reaction is inefficient, or that there are significant challenges that need to be addressed.

Improving Percentage Yield

There are several ways to improve percentage yield, such as increasing the concentration of reactants, changing the reaction conditions (e.g., temperature, pressure), using a catalyst to speed up the reaction, or using a more efficient method of product collection. Each has its own advantages and challenges.
Although it’s desirable to maximize yield, it’s not always cost-effective or safe. Hence, chemists must balance the demand for high yield with considerations such as cost, safety, and environmental impact.

Examples

For example, in the synthesis of ammonia by the Haber process, the theoretical yield is calculated from the balanced chemical equation: N2(g) + 3H2(g) → 2NH3(g). But the actual yield is usually less than this because of losses during product recovery and the fact that the reaction doesn’t go to completion under the conditions used industrially.
To calculate the percentage yield, the mass of ammonia actually produced would be divided by the maximum possible mass (calculated from the theoretical yield) and multiplied by 100.