Balance chemical equations or practice inspection balancing—smallest coefficients, steps, and a live atom-check table.
Chemistry equation balancer
Balances atoms in neutral formula equations and shows step notes plus an atom-check table. Ionic charges, electrons, and acidic/basic redox half-reactions (H⁺, OH⁻, e⁻) are not supported yet.
Balanced equation
4Fe + 3O2 → 2Fe2O3
Reactants
4Fe
3O2
Products
2Fe2O3
Balancing steps
Parse species: Fe, O2, Fe2O3.
Identify elements to conserve: Fe, O.
Solve for the smallest positive integer coefficients that balance every element.
Balanced equation: 4Fe + 3O2 → 2Fe2O3.
Verify atom counts match on both sides for each element.
Element
Reactants
Products
Fe
4
4
O
6
6
Balancing chemical equations practice set
40 inspection problems live in the Practice tab above. Formulas are locked; you only fill coefficients. Use the live atom-check table, or turn on Quiz to hide it until you check.
Intro10 equations
Diatomic elements, simple oxides, and single replacements.
Formation of water: H2 + O2 → H2O
Haber ammonia: N2 + H2 → NH3
Hydrogen chloride: H2 + Cl2 → HCl
Sodium chloride: Na + Cl2 → NaCl
Magnesium oxide: Mg + O2 → MgO
Lithium oxide: Li + O2 → Li2O
Phosphorus(V) oxide: P + O2 → P4O10
Aluminum oxide: Al + O2 → Al2O3
Iron(III) oxide: Fe + O2 → Fe2O3
Zinc + hydrochloric acid: Zn + HCl → ZnCl2 + H2
Combustion10 equations
Hydrocarbons and oxygenates: C, then H, then O (clear fractions).
Methane combustion: CH4 + O2 → CO2 + H2O
Ethane combustion: C2H6 + O2 → CO2 + H2O
Propane combustion: C3H8 + O2 → CO2 + H2O
Butane combustion: C4H10 + O2 → CO2 + H2O
Ethene combustion: C2H4 + O2 → CO2 + H2O
Ethyne (acetylene) combustion: C2H2 + O2 → CO2 + H2O
Ethanol combustion: C2H5OH + O2 → CO2 + H2O
Glucose combustion: C6H12O6 + O2 → CO2 + H2O
Octane combustion: C8H18 + O2 → CO2 + H2O
Carbon disulfide combustion: CS2 + O2 → CO2 + SO2
Polyatomic10 equations
Nitrate, sulfate, hydroxide, and phosphate as intact groups.
Chemical equation balancer, calculator, and practice
A balanced chemical equation obeys the law of conservation of mass: every atom present among the reactants must appear among the products in equal numbers. Balancing is not merely a bookkeeping exercise—it produces the stoichiometric coefficients that govern all subsequent mole-ratio calculations in reaction stoichiometry, equilibrium problems, and thermochemical equations. An unbalanced equation implies atoms are created or destroyed, which violates fundamental physical law.
The standard balancing method in general chemistry is inspection: adjust coefficients in front of compound formulas until each element has the same count on both sides. Start with elements that appear in only one reactant and one product, then move to more complex cases involving polyatomic ions that may transfer intact (such as sulfate or nitrate groups). For redox reactions, the half-reaction method or oxidation-number method provides a systematic approach when inspection becomes unwieldy.
Balanced equations appear in virtually every chemistry context. Combustion analysis requires balancing the burning reaction to relate CO₂ and H₂O produced back to the original compound. Acid–base neutralization, precipitation, and gas-evolution reactions all begin with a correctly balanced equation. In thermochemistry, coefficients scale the enthalpy change: if ΔH for forming 1 mol of product is known, doubling the coefficient doubles the enthalpy.
Students frequently struggle with balancing because they attempt to change subscripts within formulas rather than adjusting coefficients. The subscripts in H₂O, for instance, define water's identity and must never be altered—only the coefficient in front may change. The Chemical Equation Balancer on Online Science Tools is a free chemical equation calculator and balancer: it applies algorithmic balancing to valid chemical formulas, returns the smallest whole-number coefficients, and shows balancing steps with an atom-check table. Switch to Practice for a 40-equation inspection set (intro, combustion, polyatomic, challenge) with locked formulas, a live atom inventory, hints, and a quiz mode that hides the table until you check.
Correct balancing is the gateway to the Limiting Reagent Calculator and the Chemical Equilibrium Calculator. Without accurate coefficients, limiting reagent predictions and ICE table stoichiometry are wrong from the start. Treat balancing as the first step in any multi-part quantitative chemistry problem, and use our balancer to confirm your handwritten work during homework and exam preparation.
Coefficients multiply entire formulas; subscripts within formulas are fixed
Polyatomic ions unchanged on both sides can be balanced as units
Redox equations may require the half-reaction method in acidic or basic medium
The smallest whole-number coefficient set is the convention for balanced equations
Practice mode locks formulas and only lets you edit coefficients, with a live atom-check table
Formulas you will actually use
Balancing is a constraint satisfaction problem: find integer coefficients cᵢ for each species such that the total atom count of every element is identical on the reactant and product sides.
General form:
c₁·(species₁) + c₂·(species₂) + … → c₃·(species₃) + c₄·(species₄) + …
Conservation for each element X:
Σ (cᵢ × atoms of X in speciesᵢ)_reactants
= Σ (cⱼ × atoms of X in speciesⱼ)_products
Example: CH₄ + O₂ → CO₂ + H₂O
C: 1 = 1 ✓ (already balanced for carbon)
H: 4 ≠ 2 → need 2·H₂O
O: 2 ≠ 4 → need 2·O₂
Balanced: CH₄ + 2O₂ → CO₂ + 2H₂O
Fractional coefficients during balancing should be cleared by multiplying the entire equation by the denominator.
For ionic equations in aqueous solution, charge must also balance in addition to atom count.
Combustion of hydrocarbons always produces CO₂ and H₂O; balance C first, then H, then O.
Step-by-step example: Balancing the Combustion of Ethanol
Balance the combustion equation for ethanol: C₂H₅OH + O₂ → CO₂ + H₂O. Verify atom conservation on both sides.
Count atoms on the left: C = 2, H = 6, O = 1 (in ethanol) + O₂.
Balance carbon: place coefficient 2 in front of CO₂ → C₂H₅OH + O₂ → 2CO₂ + H₂O.
Balance hydrogen: 6 H on left needs 3 H₂O → C₂H₅OH + O₂ → 2CO₂ + 3H₂O.
Balance oxygen: right side has 4 + 3 = 7 O; left has 1 + 2×O₂, so 2x = 6, x = 3.
Enter C2H5OH + O2 -> CO2 + H2O into the Chemical Equation Balancer on Online Science Tools. The tool should return coefficients 1, 3, 2, 3 for ethanol, oxygen, carbon dioxide, and water respectively, matching your hand-balanced result. Use these coefficients in the Limiting Reagent Calculator if you need to compute yields, or check individual molar masses with the Stoichiometry Calculator.
Frequently asked questions
Is there a balancing chemical equations practice mode?
Yes. Switch to Practice on this page, or open /tools/balanceequation#practice. Formulas stay locked so you only edit coefficients. The set has 40 textbook equations in intro, combustion, polyatomic, and challenge groups. A live atom-check table shows which elements are still off as you type; Quiz hides the table until you check. If your coefficients are a multiple of the smallest whole-number set, the tool says so and lets you reduce.
Is this a chemical equation calculator as well as a balancer?
Yes. Enter an unbalanced equation such as Fe + O2 = Fe2O3 and the tool returns the balanced chemical equation with the smallest whole-number coefficients. It is a chemical equation balancer first; use the Limiting Reagent Calculator when you also need masses or limiting reagent.
Is this a balancing chemical equations calculator with steps?
Yes. Enter an equation such as C2H6 + O2 = CO2 + H2O and the balancer returns the balanced result, short step notes, and an element-by-element atom inventory so you can practice inspection balancing and check your work.
Can I change subscripts to balance an equation?
No. Changing a subscript alters the identity of the substance. Writing H₂O as H₂O₂ would mean hydrogen peroxide instead of water. The only permissible changes are coefficients—the numbers placed before a formula that multiply every atom in that formula. If you find yourself wanting to change a subscript, reconsider your product or reactant formulas instead.
What if the balancer gives fractional coefficients?
The Chemical Equation Balancer returns the smallest whole-number ratio by default. If you encounter fractions during manual balancing, multiply the entire equation by the least common denominator to clear them. For example, if you obtain C₂H₄ + 3.5O₂ → 2CO₂ + 3H₂O, multiply everything by 2 to get 2C₂H₄ + 7O₂ → 4CO₂ + 6H₂O.
How do I balance redox reactions in acidic solution?
Split the reaction into oxidation and reduction half-reactions. Balance atoms other than O and H first, then balance O by adding H₂O and H by adding H⁺ (in acidic medium). Balance charge by adding electrons. Multiply each half-reaction so electrons lost equal electrons gained, then add the half-reactions and cancel species appearing on both sides. For a dedicated acidic/basic medium tool with atom and charge checks, use the Redox Equation Balancer.
Why does balancing matter for enthalpy calculations?
Enthalpy of reaction ΔH is reported per mole of reaction as written. If you double all coefficients, ΔH doubles. Thermochemical equations must be balanced so the stated ΔH corresponds to the correct mole ratio of reactants and products. Using an unbalanced equation leads to enthalpy values that are off by an integer factor, producing incorrect heat predictions in calorimetry problems.
References & further reading
Standards bodies, university open courseware, and peer-reviewed references that align with the methods used on this page.
