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.

Free Limiting Reagent Calculator

Determine the limiting reagent by comparing the mole ratios of two reactants.

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Moles of Reactant A

mol

Coefficient of A

Moles of Reactant B

mol

Coefficient of B

Moles/Coefficient for A

2.0000

Moles/Coefficient for B1.5000

Moles/Coefficient for A vs Moles of Reactant A

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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

Example Calculation

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

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

Frequently Asked Questions

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