How to find the limiting reactant
The limiting reactant is the reactant that will be completely consumed first, determining the maximum amount of product formed. Identify it by converting each reactant’s mass (or moles) to moles, dividing by its stoichiometric coefficient, and the smallest resulting ratio is the limiting reactant.
Chemistry · Stoichiometry
To find the limiting reactant, start with the balanced chemical equation, then turn the given masses (or volumes) of each reactant into moles using their molar masses. Next, divide each mole amount by the coefficient that appears in the balanced equation; the smallest resulting value tells you which reactant runs out first.
Example: Combustion of propane
Follow these calculations for the reaction
- 1Write the balanced equation: .
- 2Convert masses to moles: 40 g (M=44.1 g·mol⁻¹) gives 0.91 mol; 200 g (M=32.0 g·mol⁻¹) gives 6.25 mol.
- 3Divide by coefficients: 0.91/1 = 0.91, 6.25/5 = 1.25.
- 4The smallest quotient is 0.91, so propane is the limiting reactant.
Data you need before you start
- Balanced chemical equation
- Mass or volume of each reactant
- Molar mass of each reactant
Calculated moles and quotients
| Reactant | Moles | Coefficient | Quotient |
|---|---|---|---|
| C₃H₈ | 0.91 | 1 | 0.91 |
| O₂ | 6.25 | 5 | 1.25 |
Check yourself
In the propane combustion example, which reactant is identified as limiting and why?
Get this as a lesson built for you
Describe what you are studying and Lernex writes the lesson and the questions around it. Free, and it takes about a minute.
Try itNo account needed to try it.
What people ask next
- how many moles of CO2 are produced from the limiting reactantAsk
- what if the reaction is run with excess O2, how does that change the calculationAsk
- how do I calculate percent yield after measuring actual CO2 producedAsk
- why do you convert to moles before comparing amounts
- how does a buffer resist pH change
- why does Le Chatelier's principle shift toward products
- what is the difference between Kc and Kp