Limiting Reagent Calculator Formula

Understand the math behind the limiting reagent calculator. Each variable explained with a worked example.

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Formulas Used

Moles/Coefficient for A

ratio_a = moles_a / coeff_a

Moles/Coefficient for B

ratio_b = moles_b / coeff_b

Variables

VariableDescriptionDefault
moles_aMoles of Reactant A(mol)2
coeff_aCoefficient of A1
moles_bMoles of Reactant B(mol)3
coeff_bCoefficient of B2

How It Works

How to Find the Limiting Reagent

Method

Divide the moles of each reactant by its stoichiometric coefficient. The reactant with the smallest ratio is the limiting reagent.

Ratio = moles / coefficient

Worked Example

2 mol A and 3 mol B react with coefficients 1A + 2B.

moles_a = 2coeff_a = 1moles_b = 3coeff_b = 2
  1. 01Ratio A = 2 / 1 = 2
  2. 02Ratio B = 3 / 2 = 1.5
  3. 03B has the smaller ratio, so B is the limiting reagent

Frequently Asked Questions

What is a limiting reagent?

The reactant that runs out first, determining the maximum amount of product that can form.

What happens to the excess reagent?

It is left over after the reaction completes. The remaining amount equals initial minus consumed.

Why compare ratios instead of moles?

Reactants are consumed in stoichiometric proportions, not 1:1. The ratio accounts for different coefficients.

Learn More

Guide

How to Balance Chemical Equations

Step-by-step guide to balancing chemical equations. Learn the law of conservation of mass, inspection method, tips for complex equations, and common mistakes.

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