Atom Economy and Percentage Yield

In industrial and laboratory chemistry, it is not enough to simply make a product — you need to consider how efficiently you are making it. Two key measures of efficiency are atom economy and percentage yield. They answer different questions: atom economy asks "how much of the reactant atoms end up in the desired product?" while percentage yield asks "how much product did I actually obtain compared to the maximum possible?"

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Atom Economy

Atom economy measures the proportion of reactant atoms that are converted into the desired product. It is a theoretical measure based on the balanced equation — it does not depend on how the reaction is actually carried out.

Atom economy (%) = (Mᵣ of desired product / sum of Mᵣ of all products) × 100

Alternatively (and equivalently):

Atom economy (%) = (Mᵣ of desired product × its coefficient) / (sum of Mᵣ × coefficient for all products) × 100

Worked Example 1

Calculate the atom economy for the production of ethanol by fermentation.

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂