Balancing Equations Examples in Chemistry

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

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 process of adjusting the coefficients (the numbers placed before chemical formulas) in a chemical equation so that the number of atoms of each element.

Atoms can't appear or disappear — every atom on the left must show up on the right.

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: Balancing Equations starts by naming reactants and products, then checks conservation with a balanced equation.

Common stuck point: Students often know a formula related to balancing equations but skip the recognition step: Am I tracking reactants, products, atom conservation, evidence of new substances, and the balanced equation? That leads to a correct-looking substitution attached to the wrong chemical model.

Sense of Study hint: Ask: Am I tracking reactants, products, atom conservation, evidence of new substances, and the balanced equation?

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.

Balancing Equations Mistakes

Worked Examples

Example 1

easy
Balance the equation: Fe+O2→Fe2O3\text{Fe} + \text{O}_2 \rightarrow \text{Fe}_2\text{O}_3.

Answer

4Fe+3O2→2Fe2O34\text{Fe} + 3\text{O}_2 \rightarrow 2\text{Fe}_2\text{O}_3

First step

1
Count atoms — unbalanced: Fe: 1 vs 2, O: 2 vs 3.

Full solution

  1. 2
    Balance Fe first: put 2 in front of Fe on left. Now: 2Fe+O2→Fe2O32\text{Fe} + \text{O}_2 \rightarrow \text{Fe}_2\text{O}_3. Fe balanced.
  2. 3
    Balance O: 2 on left, 3 on right. LCM of 2 and 3 is 6. Use 3O23\text{O}_2 (gives 6 O) and 2Fe2O32\text{Fe}_2\text{O}_3 (needs 6 O, but also needs 4 Fe).
  3. 4
    Update Fe: 4Fe+3O2→2Fe2O34\text{Fe} + 3\text{O}_2 \rightarrow 2\text{Fe}_2\text{O}_3. Check: Fe: 4 = 4 ✓, O: 6 = 6 ✓.
Balancing equations ensures that the same number of each type of atom appears on both sides, satisfying the law of conservation of mass.

Example 2

medium
Balance: C3H8+O2→CO2+H2O\text{C}_3\text{H}_8 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O}.

Example 3

medium
Balance: CH4+O2→CO2+H2O\text{CH}_4 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O}.

Example 4

medium
Balance: NaOH+H2SO4→Na2SO4+H2O\text{NaOH} + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + \text{H}_2\text{O}.

Example 5

medium
Balance: Pb(NO3)2+KI→PbI2+KNO3\text{Pb(NO}_3\text{)}_2 + \text{KI} \rightarrow \text{PbI}_2 + \text{KNO}_3.

Example 6

hard
Balance: Ca(OH)2+H3PO4→Ca3(PO4)2+H2O\text{Ca(OH)}_2 + \text{H}_3\text{PO}_4 \rightarrow \text{Ca}_3(\text{PO}_4)_2 + \text{H}_2\text{O}.

Practice Problems

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

Example 1

medium
Balance: Al+HCl→AlCl3+H2\text{Al} + \text{HCl} \rightarrow \text{AlCl}_3 + \text{H}_2.

Example 2

medium
Balance the equation for the formation of ammonia: N2+H2→NH3\text{N}_2 + \text{H}_2 \rightarrow \text{NH}_3.

Example 3

easy
To balance an equation you adjust which numbers?

Example 4

easy
Balance: H2+Cl2→HClH_2 + Cl_2 \rightarrow HCl.

Example 5

easy
How many oxygen atoms are on the right of →CO2+H2O\rightarrow CO_2 + H_2O (coefficients 1 and 1)?

Example 6

easy
Balance: Na+Cl2→NaClNa + Cl_2 \rightarrow NaCl.

Example 7

easy
Is Mg+O2→MgOMg + O_2 \rightarrow MgO balanced? Count oxygen.

Example 8

easy
After changing one coefficient, what must you always do?

Example 9

easy
Balance: N2+H2→NH3N_2 + H_2 \rightarrow NH_3.

Example 10

easy
If a polyatomic ion like SO4SO_4 stays intact on both sides, how should you balance it?

Example 11

medium
Balance: C3H8+O2→CO2+H2OC_3H_8 + O_2 \rightarrow CO_2 + H_2O.

Example 12

medium
Balance: Fe+O2→Fe2O3Fe + O_2 \rightarrow Fe_2O_3.

Example 13

medium
Balance: Al+HCl→AlCl3+H2Al + HCl \rightarrow AlCl_3 + H_2.

Example 14

medium
Balance: KClO3→KCl+O2KClO_3 \rightarrow KCl + O_2.

Example 15

medium
Balance with a polyatomic unit: Ca(OH)2+HNO3→Ca(NO3)2+H2O\text{Ca}(OH)_2 + HNO_3 \rightarrow Ca(NO_3)_2 + H_2O.

Example 16

medium
Why does changing H2OH_2O to H2O2H_2O_2 to balance oxygen break the rule?

Example 17

medium
Balance: C4H10+O2→CO2+H2OC_4H_{10} + O_2 \rightarrow CO_2 + H_2O.

Example 18

medium
After balancing 2H2+O2→2H2O2H_2 + O_2 \rightarrow 2H_2O, verify by counting all atoms.

Example 19

medium
Balance: P4+O2→P4O10P_4 + O_2 \rightarrow P_4O_{10}.

Example 20

challenge
Balance: Cu+HNO3→Cu(NO3)2+NO+H2OCu + HNO_3 \rightarrow Cu(NO_3)_2 + NO + H_2O.

Example 21

challenge
Balance: Fe2O3+CO→Fe+CO2Fe_2O_3 + CO \rightarrow Fe + CO_2 (blast furnace).

Example 22

challenge
Balance the combustion of glucose: C6H12O6+O2→CO2+H2OC_6H_{12}O_6 + O_2 \rightarrow CO_2 + H_2O.

Example 23

easy
Balance: Mg+O2→MgO\text{Mg} + \text{O}_2 \rightarrow \text{MgO}.

Example 24

easy
Balance: Zn+HCl→ZnCl2+H2\text{Zn} + \text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2.

Example 25

easy
Balance: Ca+O2→CaO\text{Ca} + \text{O}_2 \rightarrow \text{CaO}.

Example 26

easy
Balance: Li+Cl2→LiCl\text{Li} + \text{Cl}_2 \rightarrow \text{LiCl}.

Example 27

medium
Balance: C2H4+O2→CO2+H2O\text{C}_2\text{H}_4 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O}.

Example 28

medium
Balance: C2H6+O2→CO2+H2O\text{C}_2\text{H}_6 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O}.

Example 29

medium
Balance: Mg+HCl→MgCl2+H2\text{Mg} + \text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2.

Example 30

medium
Balance: Al+O2→Al2O3\text{Al} + \text{O}_2 \rightarrow \text{Al}_2\text{O}_3.

Example 31

medium
Balance: NH3+O2→NO+H2O\text{NH}_3 + \text{O}_2 \rightarrow \text{NO} + \text{H}_2\text{O}.

Example 32

medium
Balance: Fe+Cl2→FeCl3\text{Fe} + \text{Cl}_2 \rightarrow \text{FeCl}_3.

Example 33

hard
Balance: Ag2O→Ag+O2\text{Ag}_2\text{O} \rightarrow \text{Ag} + \text{O}_2.

Example 34

hard
Balance: Al+Fe2O3→Al2O3+Fe\text{Al} + \text{Fe}_2\text{O}_3 \rightarrow \text{Al}_2\text{O}_3 + \text{Fe} (thermite).

Example 35

hard
Balance: NaHCO3→Na2CO3+H2O+CO2\text{NaHCO}_3 \rightarrow \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2.

Example 36

hard
Balance: H2S+O2→SO2+H2O\text{H}_2\text{S} + \text{O}_2 \rightarrow \text{SO}_2 + \text{H}_2\text{O}.

Example 37

hard
Balance: Fe2(SO4)3+NaOH→Fe(OH)3+Na2SO4\text{Fe}_2(\text{SO}_4)_3 + \text{NaOH} \rightarrow \text{Fe(OH)}_3 + \text{Na}_2\text{SO}_4.

Example 38

hard
Balance: KMnO4+HCl→KCl+MnCl2+H2O+Cl2\text{KMnO}_4 + \text{HCl} \rightarrow \text{KCl} + \text{MnCl}_2 + \text{H}_2\text{O} + \text{Cl}_2.

Example 39

challenge
Balance: C2H5OH+O2→CO2+H2O\text{C}_2\text{H}_5\text{OH} + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O}.

Example 40

challenge
Balance: Cr2O72−+Fe2++H+→Cr3++Fe3++H2O\text{Cr}_2\text{O}_7^{2-} + \text{Fe}^{2+} + \text{H}^+ \rightarrow \text{Cr}^{3+} + \text{Fe}^{3+} + \text{H}_2\text{O}.
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Background Knowledge

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

chemical equation