Yield

Summary: Yield is the mass of product obtained from a chemical reaction. Percentage yield = (actual yield / theoretical yield) × 100. Actual yield is usually less than theoretical due to losses, reversible reactions, and side reactions. Tags: igcse chemistry yield calculations keyword Created: 2026-07-14 Last Updated: 2026-07-14

In chemistry, yield refers to the amount of product obtained from a chemical reaction, and there are two key measures: the theoretical yield, which is the maximum mass of product predicted by stoichiometric calculation using the balanced equation and mole ratios, and the actual yield, which is the mass of product actually collected from the experiment and is almost always smaller. The percentage yield, calculated as (actual yield divided by theoretical yield) multiplied by 100, is a measure of the efficiency of a reaction and is rarely 100% in practice due to several unavoidable factors. The main reasons for reduced yield include: reversible reactions that do not go to completion under the chosen conditions (a significant issue in industrial equilibria like the Haber and Contact processes), unwanted side reactions that consume reactants to form by-products, and mechanical losses of product during separation and purification steps such as filtration, crystallisation, evaporation, and transfer between containers. In industrial chemistry, maximising yield is economically critical — even small percentage improvements can translate to significant savings in raw material costs and waste disposal — which is why chemists carefully optimise reaction conditions of temperature, pressure, and catalyst selection. For IGCSE, students must be able to calculate theoretical yield from given reactant masses using mole calculations, compute percentage yield, and suggest plausible scientific reasons why the actual yield typically falls short of the theoretical maximum.

Key term — IGCSE Chemistry (0620/0971) glossary.