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 chemical reaction, thereby determining the maximum amount of product that can be formed.

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: Limiting Reactant starts with the given amount, names the substance, and chooses the conversion factor that cancels the old unit.

Common stuck point: Students often know a formula related to limiting reactant but skip the recognition step: Am I using a mole bridge, molar mass, formula ratio, or balanced-equation ratio to connect measured amounts? That leads to a correct-looking substitution attached to the wrong chemical model.

Sense of Study hint: Ask: Am I using a mole bridge, molar mass, formula ratio, or balanced-equation ratio to connect measured amounts?

Common Mistakes to Watch For

Before you work through the examples, skim the mistake guide so you know which shortcuts and sign errors to avoid.

Stoichiometry Mistakes

Worked Examples

Example 1

medium

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?

Answer

\text{O}_2\text{ is the limiting reactant}

First step

The reaction requires a

2:1

ratio of

\text{H}_2:\text{O}_2

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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

)

Example 3

medium

For

2\text{Al} + 3\text{Cl}_2 \rightarrow 2\text{AlCl}_3

, given 4 mol Al and 5 mol

\text{Cl}_2

, find the limiting reactant.

Example 4

medium

For

\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2

, identify the limiting reactant when 2.0 mol Mg reacts with 3.0 mol HCl.

Example 5

hard

Given 6.0 g of carbon and 16.0 g of

\text{O}_2

for

\text{C} + \text{O}_2 \rightarrow \text{CO}_2

, find the mass of

\text{CO}_2

produced.

Example 6

hard

Mix 28.0 g of

\text{N}_2

(M = 28.0) with 9.0 g of

\text{H}_2

(M = 2.0) for

\text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3

. Mass of

\text{NH}_3

produced?

Example 7

challenge

For

4\text{NH}_3 + 5\text{O}_2 \rightarrow 4\text{NO} + 6\text{H}_2\text{O}

, mix 4.0 mol

\text{NH}_3

with 6.0 mol

\text{O}_2

. How many mol of NO form and how many mol of excess remain?

Practice Problems

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

Example 1

medium

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

medium

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?

Example 3

easy

With 10 buns and 5 patties (1 each per burger), which limits the number of burgers?

Example 4

easy

A + B \rightarrow AB

, you have 3 mol A and 5 mol B. Which is limiting?

Example 5

easy

2H_2 + O_2 \rightarrow 2H_2O

, you have 2 mol

H_2

and 2 mol

O_2

. Which is limiting?

Example 6

easy

If reactant X gives 4 mol product and reactant Y gives 6 mol product, which is limiting?

Example 7

easy

N_2 + 3H_2 \rightarrow 2NH_3

with 1 mol

N_2

and 1 mol

H_2

, which is limiting?

Example 8

easy

A + 2B \rightarrow C

with 2 mol A and 2 mol B, which is limiting?

Example 9

easy

After a reaction, 0 mol of B and 2 mol of A remain. Which was limiting?

Example 10

easy

Why must you find the limiting reactant before computing product?

Example 11

medium

2H_2 + O_2 \rightarrow 2H_2O

with 4 mol

H_2

and 1 mol

O_2

, find limiting and mol

H_2O

Example 12

medium

N_2 + 3H_2 \rightarrow 2NH_3

with 2 mol

N_2

and 3 mol

H_2

, which is limiting?

Example 13

medium

2Al + 3Cl_2 \rightarrow 2AlCl_3

with 2 mol Al and 2 mol

Cl_2

, which is limiting?

Example 14

medium

A + B \rightarrow AB

with 4 g A (

M=4

) and 20 g B (

M=20

), which is limiting? (1:1)

Example 15

medium

2H_2 + O_2 \rightarrow 2H_2O

with 4 g

H_2

(

M=2

) and 16 g

O_2

(

M=32

), which is limiting?

Example 16

medium

C + O_2 \rightarrow CO_2

with 12 g C (

M=12

) and 16 g

O_2

(

M=32

), how much

CO_2

forms? (

M_{CO_2}=44

)

Example 17

medium

A + 2B \rightarrow C

with 3 mol A and 4 mol B, which is limiting and how much C?

Example 18

medium

2H_2 + O_2 \rightarrow 2H_2O

with 4 mol

H_2

and 1 mol

O_2

, how much

H_2

is left over?

Example 19

medium

Zn + 2HCl \rightarrow ZnCl_2 + H_2

with 1 mol Zn and 1 mol HCl, which is limiting?

Example 20

challenge

N_2 + 3H_2 \rightarrow 2NH_3

with 28 g

N_2

(

M=28

) and 3 g

H_2

(

M=2

), find limiting and g

NH_3

. (

M_{NH_3}=17

)

Example 21

challenge

2Al + 3Cl_2 \rightarrow 2AlCl_3

with 4 mol Al and 3 mol

Cl_2

, how much

AlCl_3

and which is in excess?

Example 22

challenge

2H_2 + O_2 \rightarrow 2H_2O

with 3 mol

H_2

and 3 mol

O_2

, how many grams of water form? (

M=18

)

Example 23

easy

A recipe needs 2 eggs and 1 cup of flour per cake. You have 10 eggs and 4 cups of flour. Which ingredient is the limiting 'reactant'?

Example 24

easy

\text{C} + \text{O}_2 \rightarrow \text{CO}_2

, you have 3 mol C and 5 mol

\text{O}_2

. Which is limiting?

Example 25

medium

For

2\text{Al} + 3\text{Cl}_2 \rightarrow 2\text{AlCl}_3

with 4 mol Al and 5 mol

\text{Cl}_2

, how many mol of

\text{AlCl}_3

form?

Example 26

medium

\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}

, you have 2 mol

\text{CH}_4

and 3 mol

\text{O}_2

. Which is limiting?

Example 27

medium

Using

\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}

with 2 mol

\text{CH}_4

and 3 mol

\text{O}_2

, how many mol of

\text{CO}_2

form?

Example 28

medium

For

\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2

with 2.0 mol Mg and 3.0 mol HCl, how many mol of

\text{H}_2

form?

Example 29

medium

2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}

, 8 g of

\text{H}_2

is mixed with 32 g of

\text{O}_2

. Which is limiting?

Example 30

hard

For

2\text{Na} + \text{Cl}_2 \rightarrow 2\text{NaCl}

, mix 4.6 g Na (M = 23.0) with 7.1 g

\text{Cl}_2

(M = 71.0). Which is limiting and how much NaCl forms?

Example 31

hard

\text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2

, mix 13.0 g Zn (M = 65.0) with 5.0 g HCl (M = 36.5). What mass of

\text{H}_2

is produced?

Example 32

hard

For

3\text{Fe} + 2\text{O}_2 \rightarrow \text{Fe}_3\text{O}_4

with 5.0 mol Fe and 4.0 mol

\text{O}_2

, find moles of

\text{Fe}_3\text{O}_4

Example 33

medium

After running

\text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3

with 2 mol

\text{N}_2

and 5 mol

\text{H}_2

, how many mol of

\text{N}_2

remain?

Example 34

medium

For

\text{S} + \text{O}_2 \rightarrow \text{SO}_2

with 3.2 g S (M = 32.0) and 3.2 g

\text{O}_2

(M = 32.0), which is limiting?

Example 35

hard

If 0.50 mol of

\text{Al}

reacts with 0.60 mol of

\text{Br}_2

2\text{Al} + 3\text{Br}_2 \rightarrow 2\text{AlBr}_3

, how many mol of

\text{AlBr}_3

form?

Example 36

medium

2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}

, you have 6 mol

\text{H}_2

and 2 mol

\text{O}_2

. Which is limiting?

Example 37

hard

Using

2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}

with 6 mol

\text{H}_2

and 2 mol

\text{O}_2

, how many mol of

\text{H}_2

are left over?

Example 38

easy

In a sandwich shop, each sandwich needs 2 slices of bread and 1 slice of cheese. With 20 slices of bread and 8 slices of cheese, which is limiting?

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Related Concepts

Stoichiometry Excess Reactant Theoretical Yield

Background Knowledge

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

stoichiometry