The Life Starter
Sign up
All courses/Life

Course 238 · Life course 60

Balance and Explain Chemical Reactions

A reaction-model sheet with atom inventories, balanced symbolic equations, a limiting-count model and an explanation of energy transfer. Six introductory lessons use supplied practice cases.

Before you start

Use paper or a free text document; every core input is supplied in the lessons.

Understand Matter with Particle Models See everything you’ll need

Free download · Original practice data · No external account required. Download the starter pack

What you’ll leave with

A reaction-model sheet with atom inventories, balanced symbolic equations, a limiting-count model and an explanation of energy transfer.

Start course Start without an account. Sign in to save lesson progress across devices.

Your project

Start with the practice files. Build your project one lesson at a time.

Practice files are free without an account. Sign in to save your project record in My Proof: a description, checklist, and optional work link. Keep the original files in your own app or notebook; saving a project record does not upload them.

  1. Get your materialsDownload practice filesSupplied practice cases, a blank working record, complete lesson instructions, and annotated worked examples.
  2. Make your projectView the project checklist Work in your own notebook, document, or software. Use the supplied practice examples when you prefer.
  3. Keep a private recordSave a project record Sign in to save a description and checklist, then return to update them.
Course handbook

Know the route before you begin.

Here’s what you’ll need and what you’ll make. You can return to this guide during any lesson.

Who this is for

Learners aged 14+ building subject foundations and practical independence. Adults can use the same supplied cases.

Prepare before lesson one
  • Use paper or a free text document; every core input is supplied in the lessons.
  • A basic calculator is optional; show the method, units and checks.
  • Suggested earlier course: Understand Matter with Particle Models
Your final project

Finish with proof you can use.

A reaction-model sheet with atom inventories, balanced symbolic equations, a limiting-count model and an explanation of energy transfer.

Save a project record in My Proof
See project checklist and review criteria

Keep your working files in your own notebook or software. Save a private description, checklist, and work link in My Proof.

What to include

  • Distinguish coefficient and subscript atom counts.
  • Classify physical, chemical and unresolved records.
  • Audit each element before and after reaction models.
  • Balance both supplied symbolic equations and independently recount atoms.
  • Track complete reaction sets and leftover paper units.
  • Account for energy transfer and include all six changed cases.

Review and revise

Use these criteria to check your work and choose what to improve.

  • Method: applies the course-specific rules to the supplied cases with visible intermediate work.
  • Accuracy: results agree with the stated facts, units, boundaries and independent checks.
  • Reasoning: explains why the result follows and identifies a limitation or unresolved question.
  • Transfer: completes changed cases and revises the final project when a relevant assumption changes.
Three ideas to help you along the way
Three useful ideas

The rules behind the steps.

01

Use the supplied mechanism

A formula’s subscripts identify the atoms in one unit of a substance; a leading coefficient counts how many such units are represented. Multiplying a coefficient changes quantity. Changing a subscript changes the represented substance. An absent subscript means one. Use paper symbols only.

02

Connect the middle steps

A balanced reaction model has the same number of each atom type before and after because atoms are rearranged rather than created or destroyed. Audit each element separately; equal total atoms alone is not enough. Counting exposes the specific mismatch that coefficients must repair.

03

Explain the final boundary

A reaction can transfer energy between the reacting system and its surroundings while conserving atoms. If the stated system loses energy and the surroundings gain it, the model is exothermic; the reverse is endothermic. Energy is not an extra atom type in the chemical equation. A temperature observation alone does not determine every energy pathway.

What do these words mean?
Key words

Key terms worth knowing.

Reactant
A substance on the input side of a reaction model.
Product
A substance formed on the output side.
Coefficient
A multiplier counting complete units in an expression.
Subscript
A count within one substance formula.
Limiting reactant
The available reactant amount that restricts possible product under the ratio.
Exothermic
Transferring energy from the stated reacting system to surroundings.
Your route

6 lessons.
One useful project.

Work in order the first time. Each lesson makes something the next lesson can use.

  1. 1
    Up next

    Read formulas and coefficients

    Count atoms using subscripts and coefficients while preserving substance identity.

  2. 2
    9 min

    Distinguish physical and chemical changes

    Classify supplied changes by substance identity and retain unresolved observations.

  3. 3
    11 min

    Audit atom counts before balancing

    Audit each element’s reactant and product counts before changing coefficients.

  4. 4
    13 min

    Balance with coefficients and verify

    Balance supplied equations using complete-unit coefficients and an independent atom recount.

  5. 5
    12 min

    Find the limiting count with paper units

    Use a balanced unit ratio to calculate complete sets, products and leftovers.

  6. 6
    15 min

    Explain reaction energy with a boundary

    Account for a supplied reaction-system energy transfer and classify its direction.

Use the tools

Tools to help you practice.

See all tools
ZIP · practice files

Balance and Explain Chemical Reactions practice files

Supplied practice cases, a blank working record, complete lesson instructions, and annotated worked examples.

Text worksheet

Your course project worksheet

A downloadable text worksheet with each lesson’s working output, space for your answers, and the shared final-project checklist. Save your own copy.

Source transparency

Sources and further study.

Explore the references behind the lessons and take your learning further. Source notes explain access and reuse.

OpenStax: physical versus chemical properties
Source & access notes · checked 2026-10-01

Web open/search showed the official page, its topic heading and relevant concept description. This is a content/source check, not a provider endorsement.

Access: Official page retrieved with the web reader on 2026-10-01; interactive tools and videos were not certified by retrieval.

Reuse: Original fictional teaching cases, calculations, questions and examples; link and short factual paraphrase only. No copied source exercises or illustrations.

OpenStax: chemical equation balancing
Source & access notes · checked 2026-10-01

Web open/search showed the official page, its topic heading and relevant concept description. This is a content/source check, not a provider endorsement.

Access: Official page retrieved with the web reader on 2026-10-01; interactive tools and videos were not certified by retrieval.

Reuse: Original fictional teaching cases, calculations, questions and examples; link and short factual paraphrase only. No copied source exercises or illustrations.

OpenStax: limiting reactants and yields
Source & access notes · checked 2026-10-01

Web open/search showed the official page, its topic heading and relevant concept description. This is a content/source check, not a provider endorsement.

Access: Official page retrieved with the web reader on 2026-10-01; interactive tools and videos were not certified by retrieval.

Reuse: Original fictional teaching cases, calculations, questions and examples; link and short factual paraphrase only. No copied source exercises or illustrations.

OpenStax: energy accounting
Source & access notes · checked 2026-10-01

Web open/search showed the official page, its topic heading and relevant concept description. This is a content/source check, not a provider endorsement.

Access: Official page retrieved with the web reader on 2026-10-01; interactive tools and videos were not certified by retrieval.

Reuse: Original fictional teaching cases, calculations, questions and examples; link and short factual paraphrase only. No copied source exercises or illustrations.

Ready when you are

Start with the first useful move.

You’ll always know what to do, what to make, and where to go next.

Start lesson one