How to Calculate Percent Yield in Chemistry
Percent yield measures the efficiency of a chemical reaction by comparing how much product was actually obtained (actual yield) to the maximum possible amount predicted by stoichiometry (theoretical yield). No reaction achieves 100% yield in practice due to incomplete reactions, side reactions, product loss during purification, and measurement errors.
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Formula
Percent Yield Calculator
Calculate the percent yield of a chemical reaction from actual and theoretical yield.
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Worked Example
Given:
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FAQs
What is the theoretical yield and how is it calculated?
Theoretical yield is the maximum amount of product predicted by the balanced chemical equation, assuming complete reaction with no losses. It is calculated using stoichiometry: find the limiting reagent, calculate moles of product from moles of limiting reagent, convert to grams using molar mass.
Why is percent yield never 100% in practice?
Yield losses occur due to: incomplete reaction (equilibrium), competing side reactions producing unwanted products, product left on glassware or filter paper, evaporation of volatile products, and measurement errors. Industrial processes are optimised to maximise yield, as even 1% improvement can save significant costs.
Can percent yield ever exceed 100%?
Theoretically no — percent yield above 100% indicates an error. Common causes include: product not fully dried (water adds mass), impurities remaining in the product, calculation error in theoretical yield, or weighing error. A yield over 100% always signals a problem with the experimental procedure or calculation.