Yield and Atom Economy

This lesson covers percentage yield and atom economy — two important measures used to evaluate chemical reactions. Both are required by the Edexcel GCSE Chemistry specification (1CH0). Understanding these concepts is essential for questions about industrial chemistry and sustainability.

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Theoretical Yield and Actual Yield

The theoretical yield is the maximum mass of product that could be formed in a reaction, based on the balanced equation and the amount of limiting reagent used. It is the amount you calculate using reacting mass calculations.

The actual yield is the mass of product that you actually obtain when you carry out the reaction in practice.

In reality, the actual yield is always less than the theoretical yield.

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Percentage Yield

Percentage yield compares the actual yield to the theoretical yield:

$\text{percentage yield} = \frac{\text{actual yield}}{\text{theoretical yield}} \times 100$percentage yield=theoretical yieldactual yield​×100

Key Points

• Percentage yield is always less than 100% in practice.
• A percentage yield of 100% would mean you obtained the maximum possible amount of product — this almost never happens.
• A higher percentage yield means less waste and a more efficient reaction.

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Why Is Yield Less Than 100%?