Chemical Equation Balancer

What is chemical equation balancing?

Balancing a chemical equation means adjusting the coefficients (the numbers in front of each formula) so that the same number of each type of atom appears on both sides of the reaction arrow. This reflects the law of conservation of mass — atoms are neither created nor destroyed in a chemical reaction, only rearranged.

An unbalanced equation like H2 + O2 -> H2O has 2 hydrogen atoms and 2 oxygen atoms on the left but 2 hydrogen and only 1 oxygen on the right. The balanced equation is 2H2 + O2 -> 2H2O, with 4 hydrogen atoms and 2 oxygen atoms on each side.

How to balance equations

Start by listing the number of each atom on both sides. Adjust coefficients for one element at a time, usually starting with the most complex molecule. Balance metals first, then nonmetals, then hydrogen, and oxygen last. Never change subscripts within a formula — only adjust the coefficients in front. Double-check that all atoms balance when finished.

How to use this tool

Enter the unbalanced equation using standard chemical notation. Use -> or = for the reaction arrow. The tool parses the formulas, applies a matrix-based balancing algorithm, and displays the balanced equation with the smallest whole-number coefficients. It also shows the atom count for each element on both sides as verification.

Types of chemical reactions

• Synthesis: A + B -> AB. Two or more substances combine to form a new compound.
• Decomposition: AB -> A + B. A compound breaks down into simpler substances.
• Single replacement: A + BC -> AC + B. One element replaces another in a compound.
• Double replacement: AB + CD -> AD + CB. Two compounds exchange partners.
• Combustion: Fuel + O2 -> CO2 + H2O. A substance reacts with oxygen, releasing energy.

Worked example

Balance the combustion of propane, C3H8 + O2 → CO2 + H2O. Balance carbon first (3 CO2), then hydrogen (4 H2O), which fixes 10 oxygen atoms on the right, so you need 5 O2 on the left. The balanced equation is C3H8 + 5 O2 → 3 CO2 + 4 H2O. Check: 3 carbon, 8 hydrogen and 10 oxygen on each side.

Common mistakes

The most common error is changing subscripts instead of coefficients — writing H2O2 to balance oxygen turns water into hydrogen peroxide, a different substance. Only the coefficients in front of a formula may change. Another slip is forgetting to balance polyatomic ions as a unit, and leaving fractional coefficients such as 5/2 O2 in a final answer where whole numbers are expected.

Frequently asked questions

Why must chemical equations be balanced?

Balanced equations satisfy the law of conservation of mass — matter cannot be created or destroyed in a chemical reaction. An unbalanced equation implies atoms appearing from nowhere or disappearing, which violates fundamental physics. Balanced equations are also necessary for stoichiometric calculations (determining how much of each reactant is needed).

Can every chemical equation be balanced?

If the equation represents a real chemical reaction, yes. However, some equations require fractional coefficients that are then multiplied to whole numbers. Nuclear reactions (which change elements) and some proposed reactions that do not actually occur cannot be balanced. If the tool cannot balance an equation, check that the formulas are correct and the reaction is chemically valid.

Can a chemical equation have fractional coefficients?

Yes. During balancing, fractions such as 5/2 O2 are valid and often appear in thermochemistry, where one mole of fuel is the reference. For a conventional balanced equation you multiply every coefficient by the smallest number that clears the fraction — here by 2 — to give whole-number coefficients.