Excess Reagent Calculator

Work out excess reagent instantly with clear inputs, formula shown and shareable results.

About Excess Reagent Calculator

Once the limiting reagent is known, the excess reagent's fate is fixed: it is consumed in strict stoichiometric proportion to the limiter and whatever remains is unreacted. Charging 8 mol where 3 mol of limiter needs 2 mol each means 6 mol reacts and 2 mol is left, a 33% excess over requirement.

Formulas

Amount required

required = limiting moles x ratio

Leftover

excess left = available - required

Worked example

With the default values below, Excess Reagent Calculator returns Excess Reagent Left Unreacted of 2.0000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Moles of the excess reagent availableminimum 0 mol: 8 mol
Moles of limiting reagentminimum 0 mol: 3 mol
Moles of excess reagent per mole of limitingminimum 0: 2

Results

Excess Reagent Left Unreacted: 2.0000 mol
Excess Reagent Consumed: 6.0000 mol
Percent Excess Charged: 33.33%
Utilisation Of The Charge: 75.00%

Step by step

1Values used
2Amount required
3Leftover
4Excess Reagent Left Unreacted= 2.0000 mol
5Excess Reagent Consumed= 6.0000 mol
6Percent Excess Charged= 33.33
7Utilisation Of The Charge= 75.00

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Is a negative leftover possible?

If it appears, the reagent you called excess is actually the limiter - the charge is below the stoichiometric requirement.

Why deliberately charge an excess?

To push an equilibrium forward or to protect an expensive reagent by making the cheap one the excess.