Limiting Reactant Calculator
Reactants (from the balanced equation)
Try an example
Limiting reactant
H₂
It runs out first. Theoretical yield: 35.744 g of H₂O (1.9841 mol).
Every reactant
| Reactant | M (g/mol) | Moles | mol ÷ coefficient | Left over |
|---|---|---|---|---|
| 2 H₂ | 2.016 | 1.9841 | 0.99206 | none (limiting) |
| 1 O₂ | 31.998 | 1.2501 | 1.2501 | 8.256 g (0.25801 mol) |
The reactant with the smallest moles ÷ coefficient limits the reaction. The equation must be balanced; this tool does not balance it for you.
Find the limiting reactant of a balanced chemical reaction from the mass of each reactant, the theoretical yield of a product, how much of each excess reactant is left over, and the percent yield when you enter the actual amount made.
Formula
Worked Example
4 g of H₂ is 1.984 mol, or 0.992 per coefficient of 2; 40 g of O₂ is 1.250 mol, or 1.250 per coefficient of 1. Hydrogen has the smaller value, so it runs out first and makes 1.984 mol (35.74 g) of water, leaving 0.258 mol of oxygen.
Frequently Asked Questions
How do you find the limiting reactant?
Convert each reactant's mass to moles, divide by its coefficient in the balanced equation, and pick the smallest result. Comparing raw masses or raw moles gives the wrong answer whenever the coefficients differ.
What is percent yield?
The amount actually obtained divided by the theoretical yield, times 100. Yields below 100% come from incomplete reactions, side reactions and losses during transfer and purification; a result above 100% usually means the product is wet or impure.
Does the equation have to be balanced?
Yes. The coefficients are the mole ratios the calculation relies on, so balance the equation first; this tool takes the coefficients as given.