Rendimento percentual

Percent yield: (actual / theoretical) × 100%

Percent yield is a measure of how efficient a reaction was. It puts the mass you actually recovered (actual yield) up against the most stoichiometry says you could have gotten (theoretical yield): %yield = (actual / theoretical) · 100%. Real reactions almost never reach 100%. Some reactant never converts, side reactions skim off material, product is lost during filtration or decantation, and equilibrium can cap how far the conversion goes. Suppose a synthesis should give 10 g of aspirin on paper but you end up with 7.5 g — that's a 75% yield. Roughly speaking, above 90% is excellent, 60 to 90% is what you'd normally expect, and anything under 50% is a sign to go back over the procedure.

Applications

Process engineers rely on it to tune industrial chemistry, and in pharmaceutical manufacturing a single percentage point can be worth millions of dollars. QA labs use it to confirm a batch performed the way it should. Academic papers report it as a measure of reaction efficiency. Anyone planning a synthesis uses it to weigh one route against another.

FAQ

Can yield exceed 100%? If it appears to, the product is almost certainly impure. Most of the time it's still holding solvent, water, or some unreacted starting material. Dry it and weigh again, or run a purity assay.

How do I compute the theoretical yield? Find the limiting reagent first. Then use the mole ratio from the balanced equation to get the moles of product, and multiply by the product's molar mass.

Why are industrial yields often lower than lab yields? Scaling up brings in heat-transfer, mixing and isolation losses that never showed up in a small flask. That's exactly why pilot plants exist, to measure the gap before it costs you at full scale.