Percentage Yields and Percentage Atom Economies

Percentage Yield: This is a comparison of the actual yield of a chemical reaction to the theoretical yield predicted by the balanced chemical equation. Calculated as (actual yield / theoretical yield) * 100.
Theoretical Yield: The maximum amount of product that can be produced from a given quantity of reactant, based on the balanced chemical equation. Calculating this involves using the balanced equation and stoichiometric coefficients.
Actual Yield: The amount of product that is actually obtained from a chemical reaction. It is often less than the theoretical yield due to incomplete reactions, side reactions, practical losses during the process, and purity of reactants.
Understanding that yield is affected by factors like reaction completion, side reactions, and practical losses is important. For instance, some reactants may not fully convert into products, thus decreasing the yield.
A reaction’s percentage yield can never exceed 100%, as this would mean more product was obtained than theoretically possible. It is closely tied to the efficiency of a chemical process.
Percentage Atom Economy: This is the measure of the proportion of reactant atoms that become part of the desired product in a chemical reaction. Calculated as (molar mass of desired product / molar mass of all reactants) * 100.
A high percentage atom economy is desirable in green chemistry and sustainable manufacturing, as it indicates that fewer atoms are wasted as by-products.
Atom economy, unlike percentage yield, can theoretically reach 100% where all atoms in the reactants become part of the desired product.
It is used in choosing between different reaction pathways in industry. Preference is given to the pathways with higher atom economies, as it minimises waste and often lowers costs.
Understanding the distinction between percentage yield and percentage atom economy is crucial. Yield describes how much desired product is made compared to what could be made, whereas atom economy describes the proportion of reactants that become the desired product.