All calculatorsLimiting Reactant Calculator
Find the limiting reactant (limiting reagent), identify what’s in excess, and compute theoretical yield using a balanced reaction. Supports inputs in moles, grams, or solution (M × L), with clear steps.
Background
In most reactions, reactants are not present in perfect stoichiometric amounts. The reactant that runs out first is the limiting reactant and it determines the maximum amount of product you can make (theoretical yield).
How to use this calculator
- Enter each reactant with its balanced coefficient.
- Enter an amount as moles, grams (with molar mass), or solution (M × L).
- Click Calculate to find the limiting reactant and theoretical yield.
How this calculator works
- Convert to moles: grams → moles using molar mass; solutions → moles using n = M × V.
- Compare “extent”: compute extent = nᵢ / coeffᵢ for each reactant.
- Limiting reactant: the smallest extent limits the reaction.
- Theoretical yield: product moles = extent × product coefficient.
Formula & Equation Used
Grams → moles: n = m / MM
Solutions: n = M × V (V in liters)
Reaction extent per reactant: extentᵢ = nᵢ / νᵢ
Theoretical product: n(product) = extent_min × ν(product)
Examples
Example 1 — 2 H₂ + O₂ → 2 H₂O
If you have 5.0 g H₂ and 20.0 g O₂, convert each to moles, compute each extent, then the smaller extent determines the limiting reactant and theoretical yield.
Example 2 — Mg + 2 HCl → MgCl₂ + H₂
Suppose you have 0.80 mol Mg and 1.00 mol HCl. Because HCl must be twice Mg, compare extents: extent(Mg)=0.80/1 and extent(HCl)=1.00/2. The smaller one is limiting.
Example 3 — 2 Al + 3 Cl₂ → 2 AlCl₃
If you have 10.0 g Al and 35.0 g Cl₂, convert to moles, divide by coefficients (2 and 3), and the smaller extent sets the maximum AlCl₃ you can form.
Frequently Asked Questions
Q: Do coefficients have to be balanced?
Yes — limiting reactant logic depends directly on correct stoichiometric coefficients.
Q: What if two reactants tie?
Then you’re at a stoichiometric mixture (both run out at the same time) within rounding.
Q: Is this actual yield?
No — this is theoretical yield (maximum possible). Real yield may be lower.
Q: Why do we divide by coefficient?
It normalizes “moles available” into “reaction batches” each reactant can support.
