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General Chemistry I · Stoichiometry

Theoretical Yield and Percent Yield

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On this page 7 sections
  1. In 30 seconds
  2. Why this matters
  3. The college version
  4. Eli explains
  5. Key takeaway
  6. Study tools
  7. Sources & references

In 30 seconds

The theoretical yield is the maximum mass of product that can form if the reaction proceeds perfectly to completion, calculated from the limiting reactant by stoichiometry. The actual yield is the mass of product actually collected in the experiment, which is almost always smaller because of incomplete reaction, side reactions, and mechanical losses during purification. Percent yield compares the two: percent yield = (actual yield / theoretical yield) × 100%, a measure of a reaction's efficiency.

Why this matters

Percent yield tells chemists whether a process is efficient enough to be practical. A pharmaceutical synthesis with 20% yield is economically hopeless, while pushing a route from 60% to 90% can decide whether a drug is affordable. Engineers track yield to price products, minimize waste, and meet environmental limits — making percent yield one of the most used numbers in real chemistry.

The college version

Key Ideas

Three yields

  • Theoretical yield: calculated maximum, from the limiting reactant.
  • Actual yield: measured in the lab after workup.
  • Percent yield: actual ÷ theoretical × 100%, the efficiency score.

Why actual < theoretical

  • The reaction may not go to completion (equilibrium).
  • Side reactions consume reactants into unwanted products.
  • Product is lost during transfer, filtration, or recrystallization.
  • Reactants may be impure.

The calculation order

  1. Identify the limiting reactant.
  2. Compute theoretical yield (mass) from it.
  3. Divide the actual yield by the theoretical yield and multiply by 100%.

Equations and Variables

  • Percent yield: % yield = (actual yield / theoretical yield) × 100%
  • Theoretical yield is computed by mass → moles → mole ratio → moles → mass, using the limiting reactant.
  • Actual yield is measured, never calculated.

How It Works (Problem-Solving Method)

  1. Balance the equation and identify the limiting reactant.
  2. Calculate theoretical yield of the product in grams from the limiting reactant.
  3. Record the actual yield (given in the problem or measured in the lab).
  4. Compute percent yield = actual / theoretical × 100%.
  5. Check that percent yield is between 0% and 100% (values above 100% signal contamination, wet product, or an error).

Worked Example

Reaction: 4 Fe + 3 O₂ → 2 Fe₂O₃. Starting with 20.0 g Fe (excess O₂), the theoretical yield of Fe₂O₃ is 28.6 g. If the student isolates 22.0 g, what is the percent yield?

  • Theoretical yield = 28.6 g Fe₂O₃ (from the earlier stoichiometry calculation).
  • Actual yield = 22.0 g.
  • Percent yield = (22.0 g / 28.6 g) × 100% = 76.9%.

Full calculation from scratch: If 1.00 mol of Fe₂O₃ is theoretically possible but only 0.850 mol is collected, percent yield = (0.850 / 1.00) × 100% = 85.0%.

Common Confusions

  • "Actual yield is calculated from the limiting reactant." — No; the theoretical yield is calculated. Actual yield is the experimentally measured amount.
  • "Theoretical yield equals the given mass of reactant." — It must be converted through the mole ratio; product and reactant have different masses.
  • "Percent yield above 100% is excellent." — It is impossible for a pure product; it signals contamination or weighing error.
  • *"Percent yield is the fraction of reactant* recovered."** — It compares product recovered to the product that could form, not reactant recovered.
Eli, the EliExplains learning guide

Eli explains

The same idea, in plain words

Explain it like I’m 10

Theoretical yield is the perfect score — what you'd bake if every drop of batter made it into the cake and nothing stuck to the bowl. Actual yield is what you actually get after the batter sticks to the bowl, some spills, and a little burns. Percent yield is your "grade": (what you got ÷ what you could've gotten) × 100. A 77% yield is like scoring 77 on a test — decent but with room to improve. The catch: real chemistry has extra reasons for losses (side reactions that make the wrong product), not just spilled batter, which is why lab yields are rarely 100%.

Key takeaways

  • Theoretical yield = maximum product from the limiting reactant.
  • Actual yield ≤ theoretical yield in practice.
  • % yield = (actual / theoretical) × 100%.
  • Percent yield over 100% indicates contamination, solvent, or error — not a miracle.
  • Theoretical yield is calculated; actual yield is measured.
  • Theoretical yield = max product from limiting reactant (calculated).
  • Actual yield = product actually isolated (measured).
  • % yield = actual / theoretical × 100%.
  • Real yields are below 100% due to loss, side reactions, and incomplete reaction.

Keep learning

Ready to build on this? Continue to the next lesson.

Practice General Chemistry I

This lesson has no separate scored set. Practice draws from the subject’s question bank.

Study tools & related lessonsYou’ll learn to · Related

You’ll learn to

  • Define theoretical yield, actual yield, and percent yield.
  • Calculate theoretical yield from the limiting reactant.
  • Compute percent yield from actual and theoretical yields.
  • Explain why actual yield is usually less than theoretical yield.

Sources & references

  1. OpenStax, "4.4 Reaction Yields." *Chemistry 2e*.
  2. OpenStax, "4.3 Reaction Stoichiometry." *Chemistry 2e*.
  3. OpenStax, "4.5 Quantitative Chemical Analysis." *Chemistry 2e*.

This lesson was adapted from the open educational references above; their licenses and attributions are preserved. See Copyright & Licensing.

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