Percentage Yield and Atom Economy in Chemistry
Percentage yield tells you how much product you actually got compared to what you theoretically should have obtained. The formula is straightforward: % yield = (actual yield ÷ theoretical yield) × 100. Getting 100% yield is nearly impossible in real experiments.
Several factors prevent you from achieving theoretical yield. Your reaction might not complete fully, side reactions could consume some reactants, or you'll lose product during purification steps. When heating hydrated salts, you might not remove all water or accidentally overheat and decompose the compound.
Atom economy measures how efficiently atoms are used in a reaction - it's the molecular mass of desired products divided by the molecular mass of all products × 100. Unlike percentage yield, atom economy considers waste production, making it crucial for sustainable chemistry.
Key Insight: Addition reactions achieve 100% atom economy because all reactants combine into one product, whilst substitution reactions create waste by-products.
Chemical companies prioritise high atom economy reactions because raw materials are expensive and limited, waste disposal costs money, and environmental regulations are strict. This makes atom economy often more valuable than percentage yield for industrial processes.
