Stoichiometry Examples: 46 Problems with Answers

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

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 branch of chemistry that uses balanced chemical equations and mole ratios to calculate the precise quantities of reactants consumed and products formed in a chemical reaction.

Using the recipe (balanced equation) to figure out how much of each ingredient you need.

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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: Stoichiometry 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 stoichiometry 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.

Moles Mistakes Stoichiometry Mistakes Balancing Equations Mistakes

Worked Examples

Example 1

medium

How many grams of

\text{O}_2

are needed to completely burn

16.0

g of

\text{CH}_4

? (

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

)

Answer

64.0 {g of O}_{2}

First step

Moles of

\text{CH}_4 = \frac{16.0}{16.04} = 0.998\,\text{mol} \approx 1.00\,\text{mol}

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Example 2

hard

How many grams of

\text{NH}_3

can be produced from

28.0

g of

\text{N}_2

and excess

\text{H}_2

? (

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

)

Example 3

medium

\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2

. Mass of CaO from 50.0 g CaCO

_3

? (

M_{\text{CaCO}_3}=100.09

M_{\text{CaO}}=56.08

)

Example 4

medium

Limiting reactant:

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

. Given

3\,\text{mol H}_2

and

2\,\text{mol O}_2

, identify limiting reactant.

Example 5

hard

Percent yield: in

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

28.0\,\text{g N}_2

with excess H

_2

yields

30.6\,\text{g NH}_3

. Find percent yield. (

M_{\text{N}_2}=28.0

M_{\text{NH}_3}=17.0

)

Example 6

hard

\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O}

. Volume of

0.250\,\text{M}

NaOH needed to neutralize

25.0\,\text{mL}

0.100\,\text{M}

HCl?

Example 7

challenge

A sample of impure

\text{CaCO}_3

weighing

5.00\,\text{g}

is heated; it releases

1.76\,\text{g CO}_2

. Find the percent purity of CaCO

_3

. (

\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2

;

M_{\text{CaCO}_3}=100.09

M_{\text{CO}_2}=44.01

)

Practice Problems

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

Example 1

medium

How many moles of

\text{H}_2\text{O}

are produced when

3.0

mol of

\text{H}_2

reacts with excess

\text{O}_2

? (

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

)

Example 2

medium

How many grams of

\text{NaCl}

form from

0.50

mol of

\text{Cl}_2

reacting with excess sodium? (

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

; molar mass of

\text{NaCl} = 58.44\,\text{g/mol}

)

Example 3

easy

2H_2 + O_2 \rightarrow 2H_2O

, how many moles of

H_2O

form from 2 mol

H_2

Example 4

easy

N_2 + 3H_2 \rightarrow 2NH_3

, what is the mole ratio of

H_2

NH_3

Example 5

easy

2H_2 + O_2 \rightarrow 2H_2O

, how many moles of

O_2

react with 4 mol

H_2

Example 6

easy

C + O_2 \rightarrow CO_2

, how many moles of

CO_2

from 3 mol

C

Example 7

easy

H_2 + O_2 \rightarrow H_2O

balanced?

Example 8

easy

2Na + Cl_2 \rightarrow 2NaCl

, how many moles of

NaCl

from 2 mol

Na

Example 9

easy

2KClO_3 \rightarrow 2KCl + 3O_2

, how many moles of

O_2

from 2 mol

KClO_3

Example 10

easy

N_2 + 3H_2 \rightarrow 2NH_3

, how many moles of

H_2

for 1 mol

N_2

Example 11

medium

2H_2 + O_2 \rightarrow 2H_2O

, how many grams of

H_2O

from 1 mol

O_2

? (

M_{H_2O}=18

)

Example 12

medium

C + O_2 \rightarrow CO_2

, how many grams of

CO_2

from 6 g of C? (C=12,

M_{CO_2}=44

)

Example 13

medium

Balance:

\_\,Al + \_\,O_2 \rightarrow \_\,Al_2O_3

. Give the coefficients.

Example 14

medium

2KClO_3 \rightarrow 2KCl + 3O_2

, how many grams of

O_2

from 1 mol

KClO_3

? (

M_{O_2}=32

)

Example 15

medium

N_2 + 3H_2 \rightarrow 2NH_3

, how many grams of

NH_3

from 1 mol

N_2

? (

M_{NH_3}=17

)

Example 16

medium

2H_2O \rightarrow 2H_2 + O_2

, how many moles of

H_2

from 36 g water? (

M=18

)

Example 17

medium

CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O

, how many moles of

O_2

to burn 0.5 mol

CH_4

Example 18

medium

2Mg + O_2 \rightarrow 2MgO

, how many grams of MgO from 2 mol Mg? (

M_{MgO}=40

)

Example 19

medium

Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2

, how many moles of Fe from 1 mol

Fe_2O_3

Example 20

challenge

CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O

, how many grams of

CO_2

from 8 g

CH_4

? (

M_{CH_4}=16

M_{CO_2}=44

)

Example 21

challenge

2H_2 + O_2 \rightarrow 2H_2O

, how many molecules of

H_2O

from 8 g

H_2

? (

M_{H_2}=2

)

Example 22

challenge

Burning 4 mol

C_2H_6

2C_2H_6 + 7O_2 \rightarrow 4CO_2 + 6H_2O

needs how many mol

O_2

Example 23

easy

For

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

, how many moles of

\text{H}_2

are needed to make

5\,\text{mol}

\text{H}_2\text{O}

Example 24

easy

For

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

, how many moles of

\text{Cl}_2

produce

0.50\,\text{mol}

NaCl?

Example 25

easy

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

. How many moles of

\text{CO}_2

from

2.5\,\text{mol}

\text{O}_2

Example 26

easy

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

. Molar mass H

_2

= 2 g/mol. Mass of

\text{H}_2

needed to react with 16 g O

_2

? (

M_{\text{O}_2}=32

)

Example 27

easy

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

. Moles NH

_3

from 0.5 mol N

_2

(excess H

_2

Example 28

medium

2\text{KClO}_3 \rightarrow 2\text{KCl} + 3\text{O}_2

. Mass of

\text{O}_2

produced from

122.55\,\text{g KClO}_3

? (

M_{\text{KClO}_3}=122.55

M_{\text{O}_2}=32.00

)

Example 29

medium

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

. Mol of HCl needed to react with

13.08\,\text{g Zn}

? (

M_{\text{Zn}}=65.38

)

Example 30

medium

For the reaction in X12, what is the maximum mass of

\text{H}_2\text{O}

produced? (

M_{\text{H}_2\text{O}}=18

)

Example 31

medium

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

. Volume of

\text{CO}_2

at STP from 32 g of CH

_4

? (

M_{\text{CH}_4}=16

)

Example 32

medium

2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}

. Mass MgO from

4.86\,\text{g Mg}

? (

M_{\text{Mg}}=24.30

M_{\text{MgO}}=40.30

)

Example 33

medium

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

. Mass Fe from

159.7\,\text{g Fe}_2\text{O}_3

? (

M=159.7

M_{\text{Fe}}=55.85

)

Example 34

hard

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

. Given

5.40\,\text{g Al}

and

20.0\,\text{g Cl}_2

, find limiting reactant and theoretical AlCl

_3

mass. (

M_{\text{Al}}=27.0

M_{\text{Cl}_2}=71.0

M_{\text{AlCl}_3}=133.5

)

Example 35

hard

\text{C}_8\text{H}_{18} + 25/2\,\text{O}_2 \rightarrow 8\text{CO}_2 + 9\text{H}_2\text{O}

(octane combustion). Mol of

\text{O}_2

to fully burn

1.00\,\text{mol C}_8\text{H}_{18}

Example 36

hard

\text{H}_2\text{SO}_4 + 2\text{NaOH} \rightarrow \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O}

. Volume of

0.500\,\text{M}

NaOH to neutralize

40.0\,\text{mL}

0.200\,\text{M}

_2

_4

Example 37

hard

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

. Volume of

\text{O}_2

at STP needed to react with

11.2\,\text{L H}_2

at STP?

Example 38

hard

Combustion of

4.40\,\text{g propane (C}_3\text{H}_8\text{)}

produces how many g CO

_2

? (

M_{\text{C}_3\text{H}_8}=44.0

M_{\text{CO}_2}=44.0

). Equation:

\text{C}_3\text{H}_8 + 5\text{O}_2 \rightarrow 3\text{CO}_2 + 4\text{H}_2\text{O}

Example 39

challenge

2\text{Al} + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2

. A student combines

10.0\,\text{g Al}

with

100\,\text{mL}

6.00\,\text{M HCl}

. Find limiting reactant, mass AlCl

_3

, and volume of H

_2

at STP. (

M_{\text{Al}}=27.0

M_{\text{AlCl}_3}=133.5

)

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Related Concepts

Mole Balancing Equations Molar Mass Limiting Reactant Theoretical Yield Percent Yield

Background Knowledge

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

molebalancing equationsmolar mass