How to Balance Chemical Equations: Steps, Methods and 8 Examples

Here is how to balance chemical equations: change only the coefficients in front of each formula until every element has the same number of atoms on both sides of the arrow. Start with the most complex compound, balance metals and other elements before hydrogen and oxygen, treat polyatomic ions that stay intact as single units, and finish by counting every atom again. For example, CH₄ + O₂ → CO₂ + H₂O balances as CH₄ + 2O₂ → CO₂ + 2H₂O.

This guide to how to balance chemical equations explains why equations must balance, the difference between coefficients and subscripts, and the inspection method step by step. It then works through eight full examples with atom-count tables, shows the algebraic method for equations that resist trial and error, adds a short note on redox half-reactions, and ends with a checking routine and the mistakes that cost students the most points.

If you only need the balance chemical equations steps in order, start with the inspection method below. The same routine works for how to balance equations in any intro chemistry course, from simple combustion reactions to equations with polyatomic ions.

Key Takeaways

• A chemical equation is balanced when each element has the same number of atoms on the reactant and product sides, and the total charge is the same on both sides.
• Balance with coefficients only. Changing a subscript changes the substance, so H₂O becomes H₂O₂, which is hydrogen peroxide.
• A reliable order is metals, then nonmetals other than H and O, then hydrogen, then oxygen. Polyatomic ions that appear unchanged on both sides can be balanced as one unit.
• Fractional coefficients are fine as a middle step. Multiply through at the end to get the smallest whole numbers.
• When inspection stalls, the algebraic method turns the equation into a small system of linear equations with one equation per element.

Why Chemical Equations Must Balance

A chemical reaction rearranges atoms. It does not create or destroy them. This is the law of conservation of mass (also called conservation of matter), and a balanced equation is simply the written proof that your reaction obeys it. OpenStax Chemistry 2e describes an equation as balanced when equal numbers of atoms of each element appear on the reactant side (left) and the product side (right).

Balancing also matters for every calculation that follows, because the coefficients become the mole ratios you use in stoichiometry.

Coefficients vs Subscripts

A coefficient is the number written in front of a formula. It tells you how many units (molecules, atoms or formula units) of that substance take part. A subscript is the small number inside a formula. It tells you how many atoms of an element are in one unit of the substance. A coefficient of 1 is usually left unwritten.

To count atoms, multiply the coefficient by every subscript that applies to that atom, including any subscript outside parentheses. In 3Ca(OH)₂, oxygen gets 3 × 1 × 2 = 6 atoms.

How to Balance Chemical Equations by Inspection

Most textbook equations are balanced by inspection, which is organized trial and error. The steps below follow the procedure in LibreTexts Introductory Chemistry.

1. Write the correct formulas. Put reactants on the left and products on the right. Remember that hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine exist as diatomic molecules (H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂) when they appear as elements.
2. Make an atom-count table. List each element (or intact polyatomic ion) and count it on each side.
3. Start with the most complex substance. Pick an element that appears in only one reactant and one product, and set coefficients so it matches.
4. Balance polyatomic ions as units if the same ion appears on both sides.
5. Balance the remaining atoms, usually ending with the simplest substance, such as O₂ or H₂. Use a fraction if you need one.
6. Clear fractions. Multiply every coefficient by the denominator.
7. Recount everything. Confirm each element matches and the coefficients are in the lowest whole-number ratio.

An Ordered Strategy: Metals, Nonmetals, Then H and O

The order you balance elements in makes a big difference. Hydrogen and oxygen often show up in several compounds at once, so fixing them early means you will undo your work later. A dependable sequence is:

1. Metals such as Fe, Al, Ca, Na and Pb.
2. Nonmetals other than H and O, such as C, N, S, P and the halogens.
3. Polyatomic ions as single units when they appear unchanged on both sides, for example SO₄²⁻, NO₃⁻ or PO₄³⁻.
4. Hydrogen.
5. Oxygen last, because a free O₂ or a water molecule can usually absorb the final adjustment.

Two shortcuts help. If oxygen ends up odd on one side and comes from O₂, use a half coefficient for O₂ and then double everything. If an element has subscript 2 on one side and 3 on the other, use their least common multiple (6) to set both coefficients.

Worked Examples of How to Balance Chemical Equations

Each example lists the unbalanced equation, the steps in order, and an atom-count table showing the counts before and after balancing.

Example 1: Combustion of Methane

Unbalanced: CH₄ + O₂ → CO₂ + H₂O

1. Carbon: 1 on each side. Already balanced.
2. Hydrogen: 4 on the left, 2 on the right. Put a 2 in front of H₂O, giving 4 H on the right.
3. Oxygen: the right side now has 2 (in CO₂) + 2 (in 2H₂O) = 4. Put a 2 in front of O₂.

Balanced: CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)

Example 2: Combustion of Propane

Unbalanced: C₃H₈ + O₂ → CO₂ + H₂O

1. Carbon: 3 on the left, so write 3CO₂.
2. Hydrogen: 8 on the left, so write 4H₂O (4 × 2 = 8).
3. Oxygen: the right side has 3 × 2 + 4 × 1 = 10 atoms. Ten oxygen atoms need 5O₂.

Balanced: C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(g)

The pattern for any hydrocarbon burning completely is the same: carbon goes to CO₂, hydrogen goes to H₂O, and oxygen is balanced last with O₂.

Example 3: Synthesis of Iron(III) Oxide

Unbalanced: Fe + O₂ → Fe₂O₃

1. Oxygen appears as 2 on the left and 3 on the right. The least common multiple is 6, so write 3O₂ and 2Fe₂O₃.
2. Iron: the right side now has 2 × 2 = 4 Fe atoms. Write 4Fe on the left.

Balanced: 4Fe(s) + 3O₂(g) → 2Fe₂O₃(s)

Here oxygen came first because it is the element that forces the largest coefficients. The metal-first rule is a default, not a law. If a metal is already balanced, move to whichever element is not.

Example 4: Single Replacement (Aluminum and Copper(II) Chloride)

Unbalanced: Al + CuCl₂ → AlCl₃ + Cu

1. Metals: Al is 1 and 1, Cu is 1 and 1. Both look balanced for now.
2. Chlorine: 2 on the left, 3 on the right. Use the least common multiple, 6: write 3CuCl₂ and 2AlCl₃.
3. Go back to the metals. Copper is now 3 on the left, so write 3Cu. Aluminum is now 2 on the right, so write 2Al.

Balanced: 2Al(s) + 3CuCl₂(aq) → 2AlCl₃(aq) + 3Cu(s)

Example 5: Double Replacement (Lead(II) Nitrate and Potassium Iodide)

Unbalanced: Pb(NO₃)₂ + KI → PbI₂ + KNO₃

The nitrate ion, NO₃⁻, appears unchanged on both sides, so count it as one unit instead of counting N and O separately.

1. Metals: Pb is 1 and 1. K is 1 and 1.
2. Iodine: 1 on the left, 2 on the right. Write 2KI.
3. Potassium is now 2 on the left. Write 2KNO₃.
4. Nitrate: 2 on the left (in Pb(NO₃)₂) and 2 on the right. Done.

Balanced: Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s) + 2KNO₃(aq)

Example 6: Polyatomic Ions (Calcium Hydroxide and Phosphoric Acid)

Unbalanced: Ca(OH)₂ + H₃PO₄ → Ca₃(PO₄)₂ + H₂O

This acid-base neutralization keeps the phosphate ion, PO₄³⁻, intact. A useful trick is to read water as HOH: one H from the acid joins one OH from the base.

1. Metal first: calcium is 1 on the left and 3 on the right. Write 3Ca(OH)₂.
2. Phosphate as a unit: 1 on the left, 2 on the right. Write 2H₃PO₄.
3. Count the pieces that form water. The left now has 3 × 2 = 6 OH groups and 2 × 3 = 6 acidic H atoms. Six H plus six OH make 6H₂O.
4. Check H and O atom by atom in the table.

Balanced: 3Ca(OH)₂(aq) + 2H₃PO₄(aq) → Ca₃(PO₄)₂(s) + 6H₂O(l)

Example 7: A Hard One (Combustion of Octane)

Unbalanced: C₈H₁₈ + O₂ → CO₂ + H₂O

1. Carbon: write 8CO₂.
2. Hydrogen: 18 atoms on the left, so write 9H₂O.
3. Oxygen: the right side has 8 × 2 + 9 × 1 = 25 atoms, an odd number. O₂ would need a coefficient of 25/2.
4. Clear the fraction by multiplying every coefficient by 2: 2C₈H₁₈ + 25O₂ → 16CO₂ + 18H₂O.

Balanced: 2C₈H₁₈(l) + 25O₂(g) → 16CO₂(g) + 18H₂O(g)

This matches the result LibreTexts gives for isooctane.

The Algebraic Method for Hard Equations

Some equations have so many interlocking elements that inspection turns into guesswork. The algebraic method replaces guessing with a system of equations. LibreTexts Linear Algebra treats balancing as a standard application: assign a variable to each coefficient, write one equation per element, and solve. If you are comfortable with substitution or elimination from solving systems of linear equations, you already have the tools.

Example 8: Potassium Permanganate and Hydrochloric Acid

Unbalanced: KMnO₄ + HCl → KCl + MnCl₂ + Cl₂ + H₂O

1. Assign variables: aKMnO₄ + bHCl → cKCl + dMnCl₂ + eCl₂ + fH₂O.
2. Write one equation per element:
   • K: a = c
   • Mn: a = d
   • O: 4a = f
   • H: b = 2f
   • Cl: b = c + 2d + 2e
3. Set a = 1. Then c = 1, d = 1, f = 4 and b = 8.
4. Substitute into the chlorine equation: 8 = 1 + 2 + 2e, so e = 5/2.
5. Multiply all values by 2 to clear the fraction: a = 2, b = 16, c = 2, d = 2, e = 5, f = 8.

Balanced: 2KMnO₄ + 16HCl → 2KCl + 2MnCl₂ + 5Cl₂ + 8H₂O

Balancing Redox Reactions with Half-Reactions

Knowing how to balance a chemical reaction that transfers electrons takes one extra rule: ionic redox equations must balance charge as well as atoms. Take copper metal in silver nitrate solution, written as ions: Cu(s) + Ag⁺(aq) → Cu²⁺(aq) + Ag(s). Each atom appears once on each side, yet the charge is +1 on the left and +2 on the right, so it is not balanced.

The half-reaction method splits the change into oxidation and reduction:

• Oxidation: Cu → Cu²⁺ + 2e⁻
• Reduction: Ag⁺ + e⁻ → Ag (multiply by 2 so electrons match)

Adding them gives Cu(s) + 2Ag⁺(aq) → Cu²⁺(aq) + 2Ag(s), with a charge of +2 on both sides. For reactions in acidic or basic solution, OpenStax Chemistry 2e, section 17.1 lays out the full routine: balance elements other than H and O, add H₂O for oxygen, add H⁺ for hydrogen, add electrons for charge, equalize electrons, then add the halves (and add OH⁻ to both sides in basic solution).

How to Check Your Answer

1. Recount every element on both sides with a fresh table, multiplying coefficients through subscripts and parentheses.
2. Check charge if any ions or electrons appear. The total charge must match.
3. Confirm the formulas are unchanged from the original equation. If a subscript moved, the answer is wrong even if the atoms match.
4. Reduce the coefficients. 4CH₄ + 8O₂ → 4CO₂ + 8H₂O is balanced but not in lowest terms. Divide by the common factor.
5. Make sure there are no fractions left, unless your instructor asks for a per-mole equation such as an enthalpy of formation.

Once the equation checks out, the coefficients become your mole ratios. To convert those to grams you will need molar masses, which our guide to calculating the molecular mass of C₆H₆ walks through step by step.

Common Mistakes When Balancing Equations

• Changing subscripts. Turning H₂O into H₂O₂ to fix oxygen creates a different chemical.
• Not multiplying through parentheses. 2Al₂(SO₄)₃ contains 4 Al, 6 S and 24 O.
• Writing diatomic elements as single atoms. Oxygen gas is O₂, not O, and chlorine gas is Cl₂.
• Treating an ion as a unit when it breaks apart. The unit shortcut only works if the same ion appears intact on both sides. In combustion or decomposition, count atoms individually.
• Stopping before the final recount. A late change to one coefficient often unbalances an element you already fixed.

For lab write-ups, our guide on how to write a chemistry lab report shows where the balanced equation belongs, and the overview of branches of chemistry shows where these skills lead.

Getting Help with Balancing Chemical Equations

Learning how to balance chemical equations takes practice, and if a particular equation keeps coming out wrong, it often helps to have someone walk through your atom-count table and show where the counts drifted. A tutor can model the inspection or algebraic method on your own problem set so you can repeat it alone. You can find step-by-step support through our chemistry homework help service.

Frequently Asked Questions

How Do You Balance a Chemical Equation?

Write correct formulas, count the atoms of each element on both sides, and adjust coefficients until every count matches. Work from the most complex compound, leave hydrogen and oxygen for last, and treat intact polyatomic ions as units. Finish by recounting and reducing to the smallest whole numbers.

What Are the Steps to Balancing a Chemical Equation?

The standard steps to balance a chemical equation are: write the unbalanced equation, make an atom-count table, balance metals, balance nonmetals other than H and O, balance polyatomic ions as units, balance hydrogen, balance oxygen, clear any fractions and recount. The same steps work for synthesis, decomposition, combustion and replacement reactions.

A Chemical Equation Is Balanced When What Is True?

A chemical equation is balanced when the number of atoms of each element is the same on both sides of the arrow. For ionic and redox equations, the total charge must also be equal on both sides. Coefficients should be in the lowest whole-number ratio.

What Does "Balance the Equation by Inserting Coefficients as Needed" Mean?

This common homework instruction means you may only add numbers in front of the formulas given. You cannot change the formulas or their subscripts. A blank in front of a formula usually means a coefficient of 1.

How Do You Easily Balance Chemical Equations?

The easiest way to learn how to balance chemical equations is to follow a fixed order: metals, other nonmetals, hydrogen, then oxygen. Use the least common multiple when an element has subscripts like 2 and 3, and allow a half coefficient for O₂ before doubling. Practice with combustion reactions first because they follow a predictable pattern.

How Do You Write and Balance a Chemical Equation from Words?

Translate each name into a correct formula, using ion charges and the diatomic rule. Put reactants left of the arrow and products right, then balance with coefficients. For example, "propane burns in oxygen to form carbon dioxide and water" becomes C₃H₈ + 5O₂ → 3CO₂ + 4H₂O.

Methods and examples follow OpenStax Chemistry 2e, LibreTexts Introductory Chemistry and LibreTexts Linear Algebra, as of Nov. 2026.