Foundation reading 8 of 17 · ~7 min

Balance atoms with coefficients

Your goal: Count each type of atom and change coefficients without changing a substance.

A focused reading from Balancing Chemical Equations. Reading time is a Chem Help estimate.

Optional prerequisite review

Review if useful. These suggestions never lock a step.

Coefficients versus subscripts

A coefficient sits in front of a formula and multiplies the whole formula unit: 2 H₂O means two water molecules, four H atoms and two O atoms. A subscript is part of the substance's identity.

Changing H₂O to H₂O₂ does not balance an equation, it replaces water with hydrogen peroxide.

Only coefficients may be changed. Touching a subscript changes the chemistry.

A reliable order of attack

1. Count every atom on both sides. 2. Balance elements that appear in exactly one substance on each side. 3. Balance polyatomic ions as whole groups when they survive the reaction intact.

4. Leave free elements such as O₂, H₂ or Na for last, since their coefficient can absorb whatever is left over. 5. Recount everything.

Keep a running atom tally in two columns. Mental counting is where most errors enter.

Sources and further reading

  • Chemistry 2e, Section 4.1: Writing and Balancing Chemical Equations
    Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson · OpenStax, Rice University · Chapter 4.1
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    Lesson-specific rights and provenance need review.

    The current online Chemistry 2e edition lists CC BY-NC-SA 4.0. The source version used for this lesson and its applicable rights remain unverified.

    Recorded use: reference. This describes the stored citation, not verified authorship or reuse permission.

    Recorded attribution / license claim (applicability unverified): Chemistry 2e, OpenStax, Rice University, licensed CC BY 4.0.

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  • General Chemistry bookshelf (LibreTexts)
    LibreTexts, University of California, Davis
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    Lesson-specific rights and provenance need review.

    The exact LibreTexts page and its license have not been established; the bookshelf citation does not grant permission for all linked material.

    Recorded use: further reading. This describes the stored citation, not verified authorship or reuse permission.

    Recorded attribution / license claim (applicability unverified): LibreTexts General Chemistry, licence varies by page, check the page footer.

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