Excess Product Calculator
Find the limiting reactant, how much of the excess reactant is used and left over, the percent excess, and the theoretical yield of product. Enter moles of each reactant with their coefficients from the balanced equation (plus the product coefficient for the yield), and the tool shows the full ICE-style breakdown with numbered steps.
Worked example, checked against this exact tool
Reaction 2Na + 2H2O → 2NaOH + H2, with 2.5 mol Na (coefficient 2) and 1.0 mol H2O (coefficient 2), product coefficient 2. Ratios: 2.5 ÷ 2 = 1.25 vs 1.0 ÷ 2 = 0.50: H2O is limiting. Reaction units = 1.0 ÷ 2 = 0.50; Na used = 0.50 × 2 = 1.0 mol; Na remaining = 2.5 - 1.0 = 1.5 mol; percent excess = 1.5 ÷ 1.0 × 100 = 150%; theoretical NaOH yield = 0.50 × 2 = 1.0 mol.
The limiting-reactant method
Divide each reactant's moles by its coefficient from the balanced equation. The smaller ratio is the limiting reactant: it runs out first and determines how far the reaction goes. The other reactant is in excess. This ratio test is equivalent to comparing how much product each reactant could make, but it needs no product math.
Excess used, excess remaining, percent excess
The reaction extent in "reaction units" is limiting moles ÷ limiting coefficient. Multiply by the excess reactant's coefficient to get the excess used; subtract from the starting amount for the excess remaining. Percent excess is remaining ÷ used × 100: 150% means half again as much as needed sits unreacted.
Theoretical yield
Theoretical yield is the maximum product the limiting reactant can make: reaction units × product coefficient. It assumes complete reaction with no side products or losses; the actual (percent) yield compares what you isolated against this number.
Working in grams
Equations speak in moles, but labs weigh grams. Convert first: moles = grams ÷ molar mass, then run the tool in moles. Convert the answers back with the same molar masses.
The manufacturing view
The same arithmetic runs factories: excess product = produced - required. A plant making 1,500 cases against demand for 1,200 holds 300 excess units. The chemistry version just adds the stoichiometric ratio step to find which "ingredient" limits production.
What competing calculators miss
The main excess-product page explains the method with examples but offers no interactive limiting-reactant tool; textbook sources show the ICE-table steps statically. This page computes the limiting reactant, excess used and remaining, percent excess, reaction extent, and theoretical yield in one pass with numbered substitution steps.
Frequently asked questions
How do you find the limiting reactant?
Divide each reactant's moles by its balanced-equation coefficient; the smaller ratio is limiting.
How do you calculate the excess reactant remaining?
Excess used = (limiting moles ÷ limiting coefficient) × excess coefficient; remaining = starting amount - used.
What is percent excess?
Remaining excess ÷ used excess × 100. 150% means 1.5 times the needed amount sits unreacted.
What is theoretical yield?
The maximum product from the limiting reactant: reaction units × product coefficient, assuming complete reaction.
What are reaction units?
Limiting moles divided by the limiting coefficient: how many times the balanced equation "runs".
Can both reactants be limiting?
When the ratios are equal, neither is in excess: both run out together at the stoichiometric ratio.
How do I work in grams instead of moles?
Convert grams to moles first (moles = grams ÷ molar mass), run the tool, then convert back.
Why does the excess reactant matter?
Leftover reactant is waste, cost, and sometimes a separation or disposal problem; minimizing excess is a core process-chemistry goal.
What is the difference between excess and limiting reactant?
The limiting reactant is consumed first and caps the product; the excess reactant is the one left over afterward.
Does this work for manufacturing too?
Yes: excess product = produced - required. The chemistry version adds the stoichiometric ratio to find the limiting input.