How do you find the limiting reactant?

Convert each reactant amount to moles, divide each amount by its balanced-equation coefficient, and identify the smallest value. That reactant is limiting.

What is theoretical yield?

Theoretical yield is the maximum product amount predicted from stoichiometry, assuming the limiting reactant reacts completely and no product is lost.

Limiting Reactant Calculator

Q: What is a limiting reactant?

The limiting reactant is the reactant that is consumed first in a chemical reaction. It determines the maximum amount of product that can form.

What the Limiting Reactant Means

The limiting reactant is the reactant that runs out first in a chemical reaction. Once the limiting reactant is consumed, the reaction cannot form more product, even if other reactants remain.

reaction extent = available moles / stoichiometric coefficient

The reactant with the smallest reaction extent is the limiting reactant.

How the Calculator Works

For each reactant, the calculator converts the available amount to moles, then divides by the coefficient in the balanced equation. The smallest coefficient-adjusted value controls the entire reaction.

limiting extent = min(n_reactant / coefficient)

Product Yield Formula

After the limiting extent is known, the amount of each product is calculated from its coefficient.

product moles = limiting extent × product coefficient

If the product molar mass is known, the calculator also converts product moles into grams.

Excess Reactant Remaining

Excess reactant remaining is found by subtracting the consumed amount from the initial amount.

remaining = initial moles − consumed moles

Percent Yield

If you enter an actual product yield, the calculator compares it with the theoretical yield.

percent yield = actual yield / theoretical yield × 100

Example: Hydrogen and Oxygen

For the reaction:

2H₂ + O₂ → 2H₂O

Suppose you have 4 mol H₂ and 1 mol O₂.

H₂ extent = 4 / 2 = 2
O₂ extent = 1 / 1 = 1

Smallest extent = 1

O₂ is limiting.
H₂ consumed = 1 × 2 = 2 mol
H₂ remaining = 4 − 2 = 2 mol
H₂O formed = 1 × 2 = 2 mol

Common Mistakes

Comparing reactant moles directly without using balanced-equation coefficients.
Using an unbalanced equation.
Forgetting to convert grams to moles before comparing reactants.
Assuming the reactant with the smallest mass is automatically limiting.
Confusing theoretical yield with actual yield.

This calculator assumes a complete reaction under ideal stoichiometric conditions. Real experiments can have side reactions, incomplete conversion, impurities, and product losses.

Frequently Asked Questions

What is a limiting reactant?

It is the reactant that is fully consumed first and controls the maximum product amount.

How do I know which reactant is in excess?

Any reactant with remaining moles after the limiting reactant is consumed is an excess reactant.

Can the calculator use grams?

Yes. Select grams as the input mode. The calculator converts grams to moles using the preset molar masses.

Can two reactants both be limiting?

Yes. If reactants are present in exact stoichiometric proportion, they can be consumed at the same time.

Does this work for any chemical reaction?

This version supports the preset balanced reactions listed in the calculator. For any custom reaction, you would need the balanced coefficients and molar masses.