Limiting Reagent Calculator
Enter an amount for every reactant to find which one runs out first, how much product forms, and what is left over.
Result
Limiting reagent
H₂
H₂ runs out first.
Theoretical yield
22.708 g NH₃
1.333 mol NH₃
Excess reactant
0.333 mol N₂ remains
9.338 g N₂
Reactant comparison
Which reactant runs out first?
| Reactant | Available | Coefficient | Moles ÷ coefficient |
|---|---|---|---|
| N₂ | 28.014 g | 1 | 1.000 |
| H₂ | 4.032 g | 3 | 0.6667 |
H₂ → limiting reagent
The smallest moles ÷ coefficient value determines which reactant runs out first.
Calculation working
From reactant amounts to NH₃
Convert each reactant to moles
28.014 g ÷ 28.014 g/mol = 1.000 mol N₂
4.032 g ÷ 2.016 g/mol = 2.000 mol H₂
Divide moles by the coefficients
N₂: 1.000 ÷ 1 = 1.000
H₂: 2.000 ÷ 3 = 0.6667
Find the smallest value
H₂ is limiting because 0.6667 is the smallest value.
Calculate the product
0.6667 × 2 = 1.333 mol NH₃
1.333 × 17.031 = 22.708 g NH₃
Excess N₂
0.6667 × 1 = 0.6667 mol N₂ consumed
1.000 − 0.6667 = 0.3333 mol N₂ remaining
0.3333 × 28.014 = 9.338 g N₂
Reaction overview
Where the numbers come from
| Substance | Role | Coefficient | Molar mass |
|---|---|---|---|
| N₂ | Reactant | 1 | 28.014 g/mol |
| H₂ | Reactant | 3 | 2.016 g/mol |
| NH₃ | Product | 2 | 17.031 g/mol |
Important concept
How do you find the limiting reagent?
- Balance the chemical equation before comparing amounts.
- Convert the amount of each reactant to moles.
- Divide each reactant's moles by its coefficient.
- The smallest result identifies the limiting reagent.
- Multiply that result by the product coefficient to get the theoretical yield.
The key calculation
Moles ÷ coefficient
The smallest result identifies the limiting reagent.
Product moles = limiting result × product coefficient
Concepts
Limiting reagents, yield, and balanced ratios
Why does the limiting reagent matter?
The reaction stops when the limiting reagent is used up, no matter how much of the other reactants you have. The limiting reagent decides the theoretical yield, and every other reactant is left over in excess.
What is theoretical yield?
The theoretical yield is the maximum amount of product that can form from the limiting reagent. Real reactions often produce less because of side reactions, losses, or incomplete reactions.
Why must the equation be balanced?
The coefficients decide how the reactants combine.
N₂ + 3H₂ → 2NH₃
For the default reaction, the balanced ratio in moles is:
1 mol N₂ + 3 mol H₂ → 2 mol NH₃
Scope
Keep this calculation focused
Enter the amount of each reactant to see which runs out first, how much product can form, and what remains.
It handles:
- Which reactant runs out first
- Theoretical yield in moles or grams
- Excess reactant remaining
- Mass or mole inputs
- Reactions with three or more reactants
- Exactly stoichiometric mixtures
Use another Chemistry Inspect tool for:
FAQ
Frequently asked questions
What is a limiting reagent?
The limiting reagent is the reactant that is used up first. Once it runs out, the reaction cannot produce any more product.
How do I find the limiting reagent?
Convert each reactant to moles, divide each mole amount by its coefficient in the balanced equation, and compare the results. The smallest result identifies the limiting reagent.
Why can't I compare the reactants by grams?
Different substances have different molar masses. Convert each amount to moles before comparing them.
Does the equation need to be balanced?
Yes. The coefficients in a balanced equation determine the mole ratios used to find the limiting reagent and theoretical yield.
What is theoretical yield?
The theoretical yield is the maximum amount of product predicted from the limiting reagent if the reaction goes to completion.
What is an excess reactant?
An excess reactant is a reactant that remains after the limiting reagent has been completely consumed.
Can there be more than one limiting reagent?
If two or more reactants reach the same minimum reaction extent, they can be consumed in exactly the required ratio. In that case, no reactant is left in excess.
Does this calculator calculate actual yield?
No. It calculates theoretical yield from the balanced equation and starting amounts. Actual yield and percent yield require experimental results.