Generated on: June 17, 2026 at 05:24 PM

Theoretical Yield Calculator

Inputs

Limiting Reactant Mass10 g
Reactant Molar Mass18.015 g/mol
Mole Ratio (product ÷ reactant)1
Product Molar Mass18.015 g/mol

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Chemistry

Theoretical Yield Calculator

Calculate the theoretical yield of a reaction from the limiting reactant mass, the molar masses, and the mole ratio from the balanced equation.

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g/mol

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Understanding theoretical yield

Theoretical yield is the maximum amount of product a reaction can make if everything goes perfectly — every bit of the limiting reactant converts to product with no losses. It sets the benchmark against which a real, measured (actual) yield is compared. Calculating it is the essential first step of almost every stoichiometry problem.

The theoretical yield method

The calculation always follows the same three steps, summarized in one formula:

mtheo=mrctMrct×r×Mprodm_{\text{theo}} = \frac{m_{\text{rct}}}{M_{\text{rct}}} \times r \times M_{\text{prod}}
SymbolQuantityUnit
m₍rct₎Mass of limiting reactantg
M₍rct₎Molar mass of limiting reactantg/mol
rMole ratio (product ÷ reactant)—
M₍prod₎Molar mass of productg/mol
m₍theo₎Theoretical yieldg

In words: convert reactant mass to moles, scale by the mole ratio from the balanced equation, then convert moles of product back to grams.

Worked example

How much water can form from 4.0 g of hydrogen in 2H₂ + O₂ → 2H₂O (with H₂ limiting)?

  1. Moles of H₂: 4.0 ÷ 2.016 = 1.98 mol
  2. Mole ratio H₂O : H₂ = 2 : 2 = 1, so moles of H₂O = 1.98 mol
  3. Mass of H₂O: 1.98 × 18.015 = 35.7 g

Finding the mole ratio

The mole ratio comes directly from the coefficients of the balanced equation — divide the product coefficient by the limiting-reactant coefficient:

ReactionProduct : reactantMole ratio
2H₂ + O₂ → 2H₂O (H₂ lim.)2 H₂O : 2 H₂1
N₂ + 3H₂ → 2NH₃ (H₂ lim.)2 NH₃ : 3 H₂0.667
2Al + 3Cl₂ → 2AlCl₃ (Al)2 AlCl₃ : 2 Al1

Identifying the limiting reactant

The limiting reactant is consumed first and caps the yield. To find it, convert each reactant to moles, divide by its coefficient in the balanced equation, and pick the smallest result. Base the theoretical yield on that reactant; the others are in excess and partly left over.

From theoretical to percent yield

Once you have the theoretical yield, weigh the product you actually recover to get the percent yield:

percent yield=actual yieldtheoretical yield×100%\text{percent yield} = \frac{\text{actual yield}}{\text{theoretical yield}} \times 100\%

Real reactions lose material to side reactions, incomplete conversion, and handling, so the actual yield — and therefore the percent yield — is almost always below 100%.

Frequently Asked Questions (FAQ)

How do you calculate theoretical yield?

Theoretical yield is found in three steps: (1) convert the limiting reactant mass to moles by dividing by its molar mass; (2) multiply by the mole ratio of product to reactant from the balanced equation; (3) convert moles of product back to grams using the product molar mass. In one expression: theoretical yield = (reactant mass ÷ reactant molar mass) × mole ratio × product molar mass.

What is the limiting reactant?

The limiting reactant is the one that is completely consumed first, stopping the reaction and setting the maximum amount of product. To identify it, convert each reactant to moles, divide by its coefficient in the balanced equation, and the smallest result is the limiting reactant. Always base a theoretical-yield calculation on the limiting reactant — the others are in excess and leftover.

How do I find the mole ratio?

The mole ratio comes straight from the coefficients of the balanced chemical equation. Divide the coefficient of the product you want by the coefficient of the limiting reactant. For example, in N₂ + 3H₂ → 2NH₃ with H₂ limiting, the ratio of NH₃ to H₂ is 2 ÷ 3 ≈ 0.667. Enter that value in the mole-ratio field.

How does theoretical yield relate to percent yield?

Theoretical yield is the ideal maximum amount of product if the reaction were perfect. Actual yield is what you really obtain, which is almost always less. Percent yield = (actual ÷ theoretical) × 100 measures the efficiency. So you calculate the theoretical yield first, then weigh your real product to find the percent yield.

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