Limiting Reagent
Enter a balanced equation and the amount of each reactant. The tool identifies the limiting reagent, the theoretical yield of your chosen product, and how much of every other reactant is left over.
How to use this tool
Find out which reactant runs out first, how much product that allows you to make, and what's left sitting in the flask. Type a balanced equation, then enter how much of each reactant you actually have.
What to enter
- Balanced equation: formulas with coefficients and one -> arrow, e.g. N2 + 3 H2 -> 2 NH3. It must already be balanced. Use the example chips for a quick start.
- Amount of each reactant: a box appears per reactant; type how much you have and pick the unit (g or mol).
- Track yield of: choose which product to report the theoretical yield for.
Reading the result
The headline is the limiting reagent: the one that runs out and caps the reaction. Below it: the theoretical yield of your chosen product (in grams and moles) and a table of how much of every excess reactant is left over.
Worked example
For N2 + 3 H2 -> 2 NH3 with 1 mol N₂ and 4 mol H₂, nitrogen is limiting: you can make 2 mol NH₃ (≈ 34 g) and 1 mol H₂ is left over.
Reaction
Result
The limiting reagent caps the reaction: the theoretical yield is the most product it can give, and the excess table shows what's left unreacted. Feed that yield into the Yield % tool to grade an actual run.
Methodology
Each reactant amount is converted to moles (mass ÷ molar mass, or entered directly). The reaction extent available from each reactant is its moles divided by its stoichiometric coefficient; the smallest extent identifies the limiting reagent.
Theoretical yield of a product = limiting extent × that product's coefficient × its molar mass. Leftover excess for every other reactant = initial moles − (limiting extent × coefficient).
Sources
- Molar masses from IUPAC 2021 conventional atomic weights (shared with the Molecular Weight tool).
Known limits
- The equation must already be balanced, this tool does not balance it for you.
- Square brackets and charges aren't parsed; rewrite coordination notation with parentheses.