What is Percent Yield?
In chemistry, a reaction rarely produces as much product as theory predicts. Percent yield measures how efficiently a reaction works by comparing what you actually get (actual yield) to what theory says you should get (theoretical yield).
Percent yield = (Actual yield / Theoretical yield) × 100%. It shows the efficiency of a reaction in producing the expected product.
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Step-by-step worked examples
A reaction theoretically produces 80 g of product, but only 64 g is obtained. Calculate percent yield.
Percent yield = (Actual / Theoretical) × 100% Percent yield = (64 / 80) × 100% Percent yield = 0.8 × 100% = 80%
In a synthesis, the theoretical yield is 120 g and actual yield is 108 g. Find the percent yield.
Percent yield = (108 / 120) × 100% Percent yield = 0.9 × 100% = 90%
A reaction has theoretical yield 150 g and actual yield 135 g. What is the percent yield?
Percent yield = (135 / 150) × 100% Percent yield = 0.9 × 100% = 90%
Flashcards
Quick quiz
Q1.Actual = 72 g, Theoretical = 90 g. Percent yield?
Q2.What does 100% percent yield mean?
Q3.Theoretical 200 g, actual 150 g. Percent yield?
Q4.Why does actual yield often differ from theoretical?
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Common mistakes
Confusing actual and theoretical yield. — Correct: Theoretical is what stoichiometry predicts; actual is what you measure.
Percent yield can be > 100%. — Correct: In theory, no — if you get more product, check for impurities or measurement error.
Ignoring units when comparing yields. — Correct: Both actual and theoretical must be in the same units (grams, moles, etc.).
Low percent yield means bad chemistry. — Correct: It's normal; identify causes (side reactions, losses) and optimize conditions.
FAQ
What is the percent yield formula?
Percent yield = (Actual yield / Theoretical yield) × 100%. It shows what fraction of predicted product you actually obtain.
How do you calculate theoretical yield?
Use stoichiometry and the limiting reactant: molar mass → mass of product.
Why is percent yield less than 100%?
Real reactions have side reactions, losses during transfer, incomplete conversion, or experimental errors.
What is a good percent yield?
Depends on reaction; 80–95% is common for well-optimized reactions. Simple reactions may exceed 90%.