Examples of Balanced Chemical Equations

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A balanced chemical equation has the same number of atoms of each element on both sides of the reaction arrow.
A balanced chemical equation has the same number of atoms of each element on both sides of the reaction arrow. (photo: Polina Tankilevitch)

A balanced chemical equation represents a chemical reaction as chemical formulas and numbers. Here is a collection of more than 10 balanced chemical equations. Use them as homework examples or to review the principles of balancing equations.

Balanced Equation Basics

  • Elements are represented using their element symbols.
  • The left side of the reaction lists the reactants, the right side lists the products, and the reaction arrow indicates the direction in which the reaction proceeds.
  • In a balanced chemical equation, the same number and type of atoms are present on both sides of the reaction arrow.
  • The number in front of a chemical formula is its coefficient and is the number of moles of that element or compound. If there is 1 mole of a substance, the number is omitted (e.g., write CO instead of 1 CO).
  • Subscripts after an element symbol indicate the number of atoms of the element in a substance. If there is no subscript, it means there is one atom of that element.
  • The total number of atoms in a compound is the subscript multiplied by the coefficient (e.g., 4H2O contains 4 x 2 = 8 atoms of hydrogen and 1 x 4 = 4 atoms of oxygen).

Balanced Chemical Equations

6 CO2 + 6 H2O → C6H12O6 + 6 O2 (balanced equation for photosynthesis)

2 AgI + Na2S → Ag2S + 2 NaI

Ba3N2 + 6 H2O → 3 Ba(OH)2 + 2 NH3

3 CaCl2 + 2 Na3PO4 → Ca3(PO4)2 + 6 NaCl

4 FeS + 7 O2 → 2 Fe2O3 + 4 SO2

PCl5 + 4 H2O → H3PO4 + 5 HCl

2 As + 6 NaOH → 2 Na3AsO3 + 3 H2

3 Hg(OH)2 + 2 H3PO4 → Hg3(PO4)2 + 6 H2O

12 HClO4 + P4O10 → 4 H3PO4 + 6 Cl2O7

8 CO + 17 H2 → C8H18 + 8 H2O

10 KClO3 + 3 P4 → 3 P4O10 + 10 KCl

SnO2 + 2 H2 → Sn + 2 H2O

3 KOH + H3PO4 → K3PO4 + 3 H2O

2 KNO3 + H2CO3 → K2CO3 + 2 HNO3

Na3PO4 + 3 HCl → 3 NaCl + H3PO4

TiCl4 + 2 H2O → TiO2 + 4 HCl

C2H6O + 3 O2 → 2 CO2 + 3 H2O

2 Fe + 6 HC2H3O2 → 2 Fe(C2H3O2)3 + 3 H2

4 NH3 + 5 O2 → 4 NO + 6 H2O

B2Br6 + 6 HNO3 → 2 B(NO3)3 + 6 HBr

4 NH4OH + KAl(SO4)2·12H2O → Al(OH)3 + 2 (NH4)2SO4 + KOH + 12 H2O

Balanced Chemical Equations as Word Equations

Sometimes you may be asked to say a balanced chemical equation as a word equation. To read an equation aloud, you need to know the chemical name of the substance. The coefficients are read as “X moles of”, the subscripts aren’t stated because they are implied in the chemical name, and the reaction arrow is read as “yields” or “forms”.

For example, the following equation:

4 NH3 + 5 O2 → 4 NO + 6 H2O

Is read as:

Four moles of ammonia plus five moles of oxygen yields four moles of nitric oxide plus six moles of water.

Check Your Work

When you write a balanced equation, you should check your work to make certain it’s balanced and that it is written in its most-reduced form.

  • Count the number of atoms of each element on both sides of the reaction arrow. They should be the same.
  • Make certain all elements are included. If an element appears on one side of the reaction, it must also appear on the other side.
  • Check to see if you can factor out the coefficients. For example, if all coefficients can be divided by 2, the equation may be balanced, but it could be written as a simpler balanced equation. Ideally, the equation should list the smallest mole ratios of reactants and products.

References

  • Brady, James E.; Senese, Frederick; Jespersen, Neil D. (2007). Chemistry: Matter and Its Changes. John Wiley & Sons. ISBN 9780470120941.
  • Crosland, M.P. (1959). “The use of diagrams as chemical ‘equations’ in the lectures of William Cullen and Joseph Black”. Annals of Science. 15 (2): 75–90. doi:10.1080/00033795900200088
  • Thorne, Lawrence R. (2010). “An Innovative Approach to Balancing Chemical-Reaction Equations: A Simplified Matrix-Inversion Technique for Determining the Matrix Null Space”. Chem. Educator. 15: 304–308.