Limiting Reactant Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Limiting Reactant.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

The reactant that is completely consumed first in a reaction, determining the maximum product yield.

If you have 10 buns and 5 patties, you can only make 5 burgers—patties are limiting.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: The limiting reactant determines the maximum possible amount of product that can form.

Common stuck point: The reactant present in smaller amount isn't always limiting—check the ratio.

Worked Examples

Example 1

medium
If 4.0 mol of \text{H}_2 reacts with 1.0 mol of \text{O}_2 in the reaction 2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}, which is the limiting reactant?

Solution

  1. 1
    The reaction requires a 2:1 ratio of \text{H}_2:\text{O}_2.
  2. 2
    For 1.0 mol \text{O}_2, we need 2 \times 1.0 = 2.0 mol \text{H}_2. We have 4.0 mol — more than enough.
  3. 3
    For 4.0 mol \text{H}_2, we need \frac{4.0}{2} = 2.0 mol \text{O}_2. We only have 1.0 mol — not enough.
  4. 4
    \text{O}_2 is the limiting reactant.

Answer

\text{O}_2\text{ is the limiting reactant}
The limiting reactant is consumed first and determines the maximum amount of product. The excess reactant has leftover moles after the reaction.

Example 2

hard
Given 10.0 g of \text{N}_2 and 10.0 g of \text{H}_2, how many grams of \text{NH}_3 can be produced? (\text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3)

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

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In a reaction \text{A} + 2\text{B} \rightarrow \text{C}, if you have 3 mol of A and 4 mol of B, which is limiting?

Example 2

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In the reaction \text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3, if you have 2.0 mol of \text{N}_2 and 5.0 mol of \text{H}_2, which reactant is limiting and how many moles of \text{NH}_3 can form?
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Background Knowledge

These ideas may be useful before you work through the harder examples.

stoichiometry