Type the unbalanced equation
Put the reactants on the left, the products on the right, and one arrow between them: C3H8 + O2 -> CO2 + H2O. Separate compounds with a plus sign. State labels such as (aq) are fine to leave in.
Balancing Equations Calculator
Use this balancing equations calculator to balance chemical reactions and understand each coefficient. Enter an unbalanced equation, check atoms on both sides, and learn the steps behind the final balanced equation.
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Your equation
Type the unbalanced reaction on one line. Use + between compounds and
->, => or = for the arrow. Groups like
Ca(OH)2 and states like (aq) are handled.
Try an example
Enter an equation and press Balance equation to get the coefficients and the atom count check.
Balanced equation
Unbalanced:
+ +
This equation was already balanced — the coefficients you entered are the simplest whole-number set.
Atom count check
| Element | Reactant atoms | Product atoms | Match |
|---|---|---|---|
Only coefficients were changed. Subscripts stay the same because they define the compounds.
This is a free balancing equations calculator: type an unbalanced reaction such as C3H8 + O2 → CO2 + H2O, press Balance equation, and you get the balanced equation together with an atom count for every element on both sides. It reads groups like Ca(OH)2 and Al2(SO4)3, accepts the arrows ->, => and =, and ignores state labels such as (s), (l), (g) and (aq). The balancing is ordinary algebra running in your browser — no AI model, no upload, nothing saved.
How to use the balancing equations calculator
Press Balance equation
The coefficients are solved as a system of linear equations, one per element, and reduced to the smallest whole numbers. Nothing is sent anywhere — the algebra runs in your browser and the same input always gives the same output.
Check the atom counts
The table under the result lists every element with its atom count on each side, so you can confirm the equation balances instead of taking the answer on trust. Only the coefficients changed; the subscripts are exactly the ones you typed.
Coefficients, subscripts, and the rule that connects them
Almost every wrong answer in this topic comes from confusing two numbers that sit next to each other and mean completely different things.
Coefficients
The number in front of a formula. It multiplies the whole compound — 2H<sub>2</sub>O is two water molecules, four hydrogens and two oxygens. Coefficients are the only thing balancing is allowed to change, and the only thing this calculator produces.
Subscripts
The small number after an element symbol. It says how many atoms of that element the compound contains, so it is part of the substance's identity. Change the 2 in H<sub>2</sub>O and you have written a different chemical, not a balanced equation.
Conservation of mass
The reason the rule exists. Atoms are rearranged in a reaction, never created or destroyed, so each element must appear in equal numbers on both sides. That single constraint is what the calculator turns into algebra.
What the equation parser understands
Type the reaction the way your textbook prints it — the two areas students get stuck on are bracketed groups and the extra notation around the arrow.
Formulas, groups and multipliers
Element symbols are case-sensitive: CO is carbon monoxide, Co is cobalt. A subscript after a closing bracket multiplies everything inside it, nested groups included, so Al2(SO4)3 resolves to 2 aluminium, 3 sulfur and 12 oxygen atoms.
- H2O, Fe2O3, C3H8
- Ca(OH)2, Mg(NO3)2
- Al2(SO4)3, (NH4)2CO3
- CuSO4·5H2O
Arrows, states and existing coefficients
Write the arrow as ->, =>, = or →. Physical states are labels rather than atoms, so they are ignored for balancing. Coefficients you have already typed are read but not trusted — the solver works out its own and tells you when yours were already correct.
- H2 + O2 -> H2O
- N2 + H2 = NH3
- Zn(s) + HCl(aq) -> ZnCl2(aq) + H2(g)
- 2H2 + O2 -> 2H2O
How to balance chemical equations
Balancing a chemical equation means choosing coefficients so each element has the same number of atoms on the reactant and product sides. You should change coefficients, not subscripts, because changing subscripts changes the substances in the reaction.
The calculator above follows the same logic a careful student does, with algebra instead of trial and error. It reads every formula into a count of atoms per element, writes one equation per element with the unknown coefficients, solves that system in whole numbers, reduces the answer to the simplest ratio, and re-counts every element before showing a result. The arithmetic is exact and no AI model is involved, so the same reaction always produces the same coefficients.
By hand, the order that gets you there with the fewest restarts is:
- Write the skeleton equation and count the atoms of each element on both sides.
- Balance the element that appears in the fewest compounds first.
- Leave free elements such as O2, H2 and Cl2 until last — they only ever appear once per side, so they absorb whatever is left over.
- Treat a polyatomic ion that survives the reaction unchanged, such as SO4, NO3 or OH, as one unit instead of as separate atoms.
- Recount everything, then reduce the coefficients to the smallest whole numbers. If a fraction appears, multiply the whole equation through to clear it.
Whatever route you take, only coefficients may change. Subscripts stay the same because they define the compounds: H2O and H2O2 are different substances, so rewriting a subscript to make a count work answers a different question than the one that was asked.
Why chemical equations have to be balanced
A balanced equation is a statement of the conservation of mass. Atoms are rearranged during a reaction, never created or destroyed, so every atom on the left has to reappear on the right. That is also why the coefficients matter well beyond this chapter: they are the mole ratios that stoichiometry, limiting-reactant and theoretical-yield questions are built on. An unbalanced equation makes every calculation downstream of it wrong, however carefully the later arithmetic is done.
Reaction types the calculator handles
The solver is general — it works from atom counts rather than from a list of recognised reactions — so the reaction families school chemistry covers are all in scope:
- Synthesis: N2 + 3H2 → 2NH3
- Decomposition: 2H2O2 → 2H2O + O2
- Single replacement: 2Al + 6HCl → 2AlCl3 + 3H2
- Double replacement: Al2(SO4)3 + 3Ca(OH)2 → 2Al(OH)3 + 3CaSO4
- Combustion: C3H8 + 5O2 → 3CO2 + 4H2O
- Acid–base neutralisation: Ca(OH)2 + 2HCl → CaCl2 + 2H2O
Redox reactions balance here too whenever mass balance alone settles them. Half-reaction problems that also need electrons and charge balanced in acidic or basic solution belong in the redox reaction balancer instead.
Common mistakes when balancing equations
Common mistakes include changing subscripts, forgetting diatomic molecules such as O2 and H2, balancing oxygen or hydrogen too early in combustion problems, and not reducing coefficients to the simplest whole-number ratio.
Two more are worth naming. Miscounting inside a bracketed group is the most frequent arithmetic slip: Ca(OH)2 holds two oxygens and two hydrogens, not one of each, and Al2(SO4)3 holds twelve oxygens. And stopping one element early — fixing carbon, then hydrogen, and never re-checking carbon after the last change — leaves an equation that looks finished but is not. The atom count table above exists for exactly that final check.
Balancing equations examples
These reactions are balanced by the same algebra the calculator runs, so the coefficients and the atom counts below are the tool's own output. Type any other reaction above to get the same table for your equation.
Example 1: Hydrogen burning to water
Unbalanced equation: H2 + O2 → H2O
Balanced equation: 2H2 + O2 → 2H2O
| Element | Reactant atoms | Product atoms |
|---|---|---|
| H | 4 | 4 |
| O | 2 | 2 |
Water needs an even number of oxygen atoms, so the coefficient 2 on H2O comes first and the hydrogens follow.
Example 2: Iron rusting to iron(III) oxide
Unbalanced equation: Fe + O2 → Fe2O3
Balanced equation: 4Fe + 3O2 → 2Fe2O3
| Element | Reactant atoms | Product atoms |
|---|---|---|
| Fe | 4 | 4 |
| O | 6 | 6 |
Three oxygens on the right against a diatomic O2 on the left forces the whole equation to be doubled to clear the fraction.
Example 3: Combustion of propane
Unbalanced equation: C3H8 + O2 → CO2 + H2O
Balanced equation: C3H8 + 5O2 → 3CO2 + 4H2O
| Element | Reactant atoms | Product atoms |
|---|---|---|
| C | 3 | 3 |
| H | 8 | 8 |
| O | 10 | 10 |
Carbon and hydrogen are balanced from the hydrocarbon first; oxygen is left until last because it appears in both products.
Example 4: Single replacement: aluminium in hydrochloric acid
Unbalanced equation: Al + HCl → AlCl3 + H2
Balanced equation: 2Al + 6HCl → 2AlCl3 + 3H2
| Element | Reactant atoms | Product atoms |
|---|---|---|
| Al | 2 | 2 |
| H | 6 | 6 |
| Cl | 6 | 6 |
Hydrogen leaves as diatomic H2, so the hydrogens on the right must come out even.
Example 5: Acid-base neutralisation with a bracketed group
Unbalanced equation: Ca(OH)2 + HCl → CaCl2 + H2O
Balanced equation: Ca(OH)2 + 2HCl → CaCl2 + 2H2O
| Element | Reactant atoms | Product atoms |
|---|---|---|
| Ca | 1 | 1 |
| O | 2 | 2 |
| H | 4 | 4 |
| Cl | 2 | 2 |
The bracket subscript applies to both the O and the H, so Ca(OH)2 supplies two oxygens and two hydrogens.
Example 6: Double replacement with polyatomic ions
Unbalanced equation: Al2(SO4)3 + Ca(OH)2 → Al(OH)3 + CaSO4
Balanced equation: Al2(SO4)3 + 3Ca(OH)2 → 2Al(OH)3 + 3CaSO4
| Element | Reactant atoms | Product atoms |
|---|---|---|
| Al | 2 | 2 |
| S | 3 | 3 |
| O | 18 | 18 |
| Ca | 3 | 3 |
| H | 6 | 6 |
Sulfate and hydroxide pass through the reaction unchanged, so treating each as a single unit is faster than counting atoms.
Related chemistry calculators
- Work the reasoning through the whole problem with the AI chemistry solver.
- Turn a formula into a molar mass with the molecular weight calculator.
- Take the balanced coefficients into mole ratios and yield with the stoichiometry calculator.
- Convert moles, mass and volume into concentration with the molarity calculator.
- Handle acid and base strength separately with the pH calculator.
- Balance half-reactions with electrons and charge in the redox reaction balancer.
Other chemistry tools
Frequently Asked Questions
What is a balancing equations calculator?
A balancing equations calculator helps find the coefficients needed to make the number of atoms equal on both sides of a chemical equation. This one parses each formula into atom counts, solves the resulting system of linear equations in whole numbers, reduces the coefficients to the simplest ratio, and then re-counts every element before showing you the result. It is ordinary algebra rather than an AI model, which is why the answer is reproducible: the same reaction typed twice returns the same coefficients both times.
Can I change subscripts when balancing a chemical equation?
No. You should only change coefficients. Changing subscripts changes the chemical formula and creates a different substance. Turning H₂O into H₂O₂ to make the oxygens work out swaps water for hydrogen peroxide, which is a different reaction entirely. The calculator enforces this: it returns the compounds exactly as you typed them and only ever adds a number in front of a formula.
Why do chemical equations need to be balanced?
Chemical equations must be balanced because matter is conserved. The atoms present before a reaction must also be present after the reaction. The practical consequence is that the coefficients are the mole ratios everything else depends on — limiting reactant, theoretical yield, and any mass or volume calculation you make from the reaction. Balance the equation wrong and every number after it is wrong too, however careful the later arithmetic is.
Does the calculator show steps?
It shows the atom counts and the coefficient choices so you can learn the balancing process instead of only copying the final answer. Each result comes with a table listing every element with its atom count on the reactant and product sides, so you can check the equation the way an examiner would. The reasoning behind a particular reaction — why oxygen is left until last in a combustion problem, for instance — is explained in the worked examples below and by the EduSolver AI chemistry tutor.
What types of equations can it balance?
It supports common school chemistry equations such as synthesis, decomposition, single replacement, double replacement, combustion, and acid-base reactions. The solver works from atom counts rather than from a list of recognised reaction types, so anything that balances on mass alone will balance here, including formulas with nested groups such as Al₂(SO₄)₃. Redox problems that also require electron and charge balancing in acidic or basic solution are a separate job — use the redox reaction balancer for those.
Stuck on the chemistry around the balanced equation?
EduSolver's AI tutor reads the whole problem, works the stoichiometry after the coefficients, and explains each step — then turns it into flashcards for the test.