⚗️ Free Chemistry Tool
Free Chemical Equation Balancer — Instant Step-by-Step Solutions
Balance any chemical equation instantly with full step-by-step working shown. Supports combustion, redox, acid-base, decomposition reactions and more. Perfect for chemistry homework, lab reports, and exam preparation. No sign-up, completely free.
Chemical Equation Balancer — Enter equation or pick from library
Quick examples — click to load:
H₂ + O₂ → H₂O
CH₄ + O₂ → CO₂ + H₂O
Fe + O₂ → Fe₂O₃
Na + H₂O → NaOH + H₂
KMnO₄ + HCl →
C₃H₈ + O₂ →
Al + O₂ → Al₂O₃
NaOH + HCl →
—
—
| Element | Reactants | Products | Balanced? |
|---|
How to enter equations: Use element symbols with numbers (H2, O2, CO2, Fe2O3). Use + between compounds and → or = as the arrow. Subscript numbers go after the element (H2O not H₂O). Coefficients go before compounds (2H2O).
Reactants
Products
Step by Step
How to balance a chemical equation — complete guide
Balancing a chemical equation means making sure the number of atoms of each element is equal on both sides. This follows the Law of Conservation of Mass — matter cannot be created or destroyed.
Reactants → Products | Atoms in = Atoms out
The 5-step method to balance any equation
01
Write the unbalanced equation
Write the correct formulas for all reactants and products. Never change a formula — only add coefficients.
02
Count atoms on each side
Make a table listing each element and how many atoms appear on the left and right sides.
03
Start with the most complex compound
Balance the compound with the most elements first. Then work outward to simpler compounds.
04
Balance H and O last
Hydrogen and oxygen are usually the easiest to balance at the end. Save them for last.
05
Use whole number coefficients only
Coefficients must be whole numbers. If you get fractions, multiply all coefficients by the denominator.
Worked example: Balance CH₄ + O₂ → CO₂ + H₂O
Step 1 — Write unbalanced equation:
CH₄ + O₂ → CO₂ + H₂O
Step 2 — Count atoms: Left: C=1, H=4, O=2 | Right: C=1, H=2, O=3 → Not balanced
Step 3 — Balance Carbon first: C is already 1 on each side ✓
Step 4 — Balance Hydrogen: Left has 4H, right has 2H → Put coefficient 2 before H₂O
CH₄ + O₂ → CO₂ + 2H₂O → Now H: 4=4 ✓
Step 5 — Balance Oxygen: Right now has O: 2+2=4. Left has O=2 → Put coefficient 2 before O₂
CH₄ + 2O₂ → CO₂ + 2H₂O → O: 4=4 ✓
Final balanced equation: CH₄ + 2O₂ → CO₂ + 2H₂O
Step 2 — Count atoms: Left: C=1, H=4, O=2 | Right: C=1, H=2, O=3 → Not balanced
Step 3 — Balance Carbon first: C is already 1 on each side ✓
Step 4 — Balance Hydrogen: Left has 4H, right has 2H → Put coefficient 2 before H₂O
CH₄ + O₂ → CO₂ + 2H₂O → Now H: 4=4 ✓
Step 5 — Balance Oxygen: Right now has O: 2+2=4. Left has O=2 → Put coefficient 2 before O₂
CH₄ + 2O₂ → CO₂ + 2H₂O → O: 4=4 ✓
Final balanced equation: CH₄ + 2O₂ → CO₂ + 2H₂O
Common balanced equations reference
| Reaction | Balanced Equation | Type |
|---|---|---|
| Hydrogen + Oxygen | 2H₂ + O₂ → 2H₂O | Synthesis |
| Methane combustion | CH₄ + 2O₂ → CO₂ + 2H₂O | Combustion |
| Iron rusting | 4Fe + 3O₂ → 2Fe₂O₃ | Synthesis |
| Sodium + water | 2Na + 2H₂O → 2NaOH + H₂ | Redox |
| Ammonia synthesis | N₂ + 3H₂ → 2NH₃ | Synthesis |
| Water electrolysis | 2H₂O → 2H₂ + O₂ | Decomposition |
| NaOH + HCl | NaOH + HCl → NaCl + H₂O | Acid-Base |
| Calcium carbonate decomposition | CaCO₃ → CaO + CO₂ | Decomposition |
Reference
Types of chemical reactions
Combustion
Fuel + O₂ → CO₂ + H₂O
CH₄ + 2O₂ → CO₂ + 2H₂O
A substance reacts with oxygen to produce carbon dioxide and water. Common in burning hydrocarbons.
Synthesis (Combination)
A + B → AB
2H₂ + O₂ → 2H₂O
Two or more substances combine to form a single product. Also called combination reactions.
Decomposition
AB → A + B
2H₂O → 2H₂ + O₂
A single compound breaks down into two or more simpler substances. Opposite of synthesis.
Single Displacement
A + BC → AC + B
Zn + 2HCl → ZnCl₂ + H₂
One element replaces another in a compound. More reactive element displaces the less reactive one.
Double Displacement
AB + CD → AD + CB
AgNO₃ + NaCl → AgCl + NaNO₃
Ions of two compounds exchange partners. Includes precipitation and neutralization reactions.
Acid-Base (Neutralization)
Acid + Base → Salt + H₂O
HCl + NaOH → NaCl + H₂O
An acid reacts with a base to form a salt and water. Always produces a neutral product.
Why Us
Why use this chemical equation balancer?
⚡
Instant balancing
Enter any equation and get the balanced version with coefficients instantly — no manual trial and error needed.
📐
Steps always shown
Every result comes with a full step-by-step method so you learn how to balance equations yourself for exams.
📚
30+ reaction library
Browse pre-balanced equations sorted by type — combustion, redox, acid-base, decomposition, and more.
✅
Atom verification table
See a full atom count table confirming each element is balanced on both sides of the equation.
🔢
Mole ratio calculator
Automatically extract mole ratios from any balanced equation for use in stoichiometry calculations.
🔓
100% free, no sign-up
No account, no email, no limits. Works on any device — built for chemistry students who need fast answers.
FAQ
Frequently asked questions about balancing chemical equations
To balance a chemical equation: (1) Write the unbalanced equation with correct formulas. (2) Count atoms of each element on both sides. (3) Add whole-number coefficients in front of compounds to make atom counts equal. (4) Never change subscripts inside formulas. (5) Start with the most complex compound and balance H and O last. Verify by recounting atoms on both sides.
Unbalanced: H₂ + O₂ → H₂O. Count atoms: Left H=2, O=2. Right H=2, O=1. Oxygen is unbalanced. Put coefficient 2 before H₂O: H₂ + O₂ → 2H₂O. Now H: left=2, right=4 — unbalanced. Put coefficient 2 before H₂: 2H₂ + O₂ → 2H₂O. Check: H=4=4 ✓, O=2=2 ✓. Balanced equation: 2H₂ + O₂ → 2H₂O.
Step 1: C is balanced (1=1). Step 2: Balance H — left has 4H, right has 2H, so put 2 before H₂O: CH₄ + O₂ → CO₂ + 2H₂O. Step 3: Balance O — right now has 4O, left has 2O, so put 2 before O₂: CH₄ + 2O₂ → CO₂ + 2H₂O. Verify: C=1=1 ✓, H=4=4 ✓, O=4=4 ✓. Balanced.
The Law of Conservation of Mass states that matter cannot be created or destroyed in a chemical reaction. The total mass of reactants must equal the total mass of products. This is why chemical equations must be balanced — the number of atoms of each element must be the same on both sides of the equation.
Subscripts define the chemical formula of a compound. Changing a subscript changes the compound entirely — H₂O is water, but H₂O₂ is hydrogen peroxide. You can only add coefficients (numbers in front of a formula) to change how many molecules are present, not the molecule itself.
This is a common equation. Unbalanced: Fe + O₂ → Fe₂O₃. Balance Fe: right has 2Fe, so put 2 before Fe: 2Fe + O₂ → Fe₂O₃. Balance O: right has 3O, left needs 3O from O₂ (which comes in pairs). LCM of 2 and 3 is 6, so use 3O₂ and 2Fe₂O₃: 4Fe + 3O₂ → 2Fe₂O₃. Verify: Fe=4=4 ✓, O=6=6 ✓.
A combustion reaction occurs when a fuel (usually a hydrocarbon) reacts with oxygen to produce carbon dioxide and water. The general form is: Fuel + O₂ → CO₂ + H₂O. Examples include the burning of methane (CH₄), propane (C₃H₈), and ethanol (C₂H₅OH). Complete combustion produces CO₂; incomplete combustion produces CO.
Redox reactions involve both oxidation (loss of electrons) and reduction (gain of electrons). To balance them: (1) Assign oxidation numbers to all elements. (2) Identify which elements are oxidized and reduced. (3) Balance electrons transferred using the half-reaction method or oxidation number method. (4) Then balance remaining atoms and charge. Redox equations like KMnO₄ + HCl are complex and often require the half-reaction method.
Mole ratios are the ratios of coefficients in a balanced equation. In CH₄ + 2O₂ → CO₂ + 2H₂O, the mole ratio is 1:2:1:2. This means 1 mole of CH₄ reacts with 2 moles of O₂ to produce 1 mole of CO₂ and 2 moles of H₂O. Mole ratios are used in stoichiometry to calculate how much of each substance is needed or produced.