Limiting and excess reagent analysis

Limiting Reactant Calculator

Compare the available amount of every reactant against its stoichiometric coefficient. The smallest reaction extent identifies the limiting reactant and sets product yield and excess remaining.

Browser-side calculationStep-by-step resultEducational use

Limiting Reactant Calculator

Calculator

Enter a balanced equation and a finite quantity for every reactant. The form updates to match the reactant side of the equation.

Inputs
The equation controls the reactant fields below. Enter one available quantity for every reactant.

Example: 2H2 + O2 -> 2H2O

Available reactants

All 2 reactant quantities are required.

2 H₂

Reactant 1

O₂

Reactant 2

Optional, in g/mol.

Load an example

Result
Reactants within a 1×10⁻⁹ relative capacity tolerance are reported together. Displayed numbers use at most eight significant digits.
Enter every reactant quantity and select Find limiting reactant to see the limiting status, excess remaining, and product yield.
reaction extent = min(reactant moles / coefficient); remaining moles = available − coefficient × extent

Calculation method

How the calculation works

Step 1
Normalize every reactant
Convert amount, mass, or molarity with volume into moles for each reactant in the balanced equation.
Step 2
Compare reaction extents
Divide each available mole amount by its coefficient. The smallest value limits the reaction; values within the stated tolerance are co-limiting.
Step 3
Calculate products and leftovers
Multiply the limiting extent by each coefficient, then subtract consumed reactant and calculate the selected product yield.

Worked examples

Check the result by hand

Oxygen limits water formation
For 2H2 + O2 -> 2H2O, mix 5.0 mol H2 with 2.0 mol O2.
  1. 1.H2 capacity is 5.0 / 2 = 2.5 mol of reaction extent.
  2. 2.O2 capacity is 2.0 / 1 = 2.0 mol, so O2 is limiting.
  3. 3.Consume 4.0 mol H2 and form 4.0 mol H2O.
O2 is limiting, 1.0 mol H2 remains, and 4.0 mol H2O can form.
Hydrogen limits ammonia formation
For N2 + 3H2 -> 2NH3, mix 1.0 mol N2 with 2.0 mol H2.
  1. 1.N2 capacity is 1.0 / 1 = 1.0 mol of reaction extent.
  2. 2.H2 capacity is 2.0 / 3 = 0.6667 mol, so H2 is limiting.
  3. 3.Multiply the limiting extent by the NH3 coefficient 2.
H2 is limiting and the theoretical product amount is 1.333 mol NH3.

Scope

Assumptions and limits

These limits keep the result reproducible and make unsupported inputs visible instead of guessing.

Every reactant shown by the balanced equation needs a finite, non-negative quantity.
Reactants whose capacities differ by no more than the displayed relative tolerance are reported as co-limiting.
A stoichiometric mixture means all supplied reactants reach zero together within that tolerance.
For solution inputs, remaining solute is reported in moles because the final mixed volume is not known.
Data and terminology sources: CIAAW Abridged Standard Atomic Weights 2024, IUPAC Gold Book, extent of reaction.

Limiting Reactant Calculator FAQ

Frequently asked questions

How does the calculator identify the limiting reactant?

It converts each reactant to moles and divides by that reactant coefficient. The smallest quotient is the reaction extent available before a reactant runs out.

What is a stoichiometric mixture?

Every reactant is present in the exact coefficient ratio, within the calculation tolerance. No reactant remains in excess after the reaction reaches its maximum extent.

Why is solution remainder shown in moles?

Molarity after mixing depends on final solution volume. Since the calculator does not assume additive volumes, it reports the chemically determined remaining mole amount.

Related chemistry tools
Continue the same calculation with a tool that handles the next chemistry task.
Stoichiometry Calculator

Convert one known amount to one target species.