Chemical Equations

Type any reaction and get the smallest whole-number coefficients that make every element — and the charge, for ions and half-reactions — the same on both sides. Check your own coefficients too: the page says whether they balance.

StoichiometryEquationsRedox

Inputs

Input examples

Type _ for a subscript (H_2 gives H₂) and ^ for a charge (Fe^3+ gives Fe³⁺); -> becomes an arrow. Plain H2O works too. The keyboard button in the field has a chemistry tab with elements, charges, states and arrows. Write -> between reactants and products and + between substances. Brackets and hydrates work: Ca(OH)2, CuSO4·5H2O. Write charges with ^: Fe^3+, SO4^2-, or a single sign for charge 1: Na+, Cl-. An electron is e. States such as (aq) are allowed and ignored. Type coefficients yourself to have them checked.

Reaction

C_{3}H_{8}+O_{2}\rightarrow CO_{2}+H_{2}O

Why Balance an Equation?

Atoms are not created or destroyed in a chemical reaction, they only change partners. So every element must appear the same number of times on both sides. The coefficients in front of the formulas say how many of each molecule take part; the formulas themselves never change.

Each element gives one equation in the unknown coefficients, and a charge balance adds one more for ions. This page solves that set of equations exactly, with fractions, and scales the answer to the smallest whole numbers. If there is no solution, a formula is wrong; if there are several, the equation is really two reactions mixed together.

atomssame on both sides

chargesame on both sides

formulasnever change

massis conserved

Atoms on Each Side

balanced

reactant side

product side

Result

Enter a reaction above

Atom Count

with the balanced coefficients

Element	Reactants	Products	Check

Worked Techniques

By Inspection

Start with the element in the fewest substances (C: 3 CO₂), then H (4 H₂O), and balance O last because O₂ contains nothing else.

Example: oxygen on the right: 3·2 + 4 = 10 atoms, so 5 O₂.

Algebra

Give every coefficient a letter and write one equation per element. Choose one letter, solve the rest and clear the fractions.

Example: c = 2 gives a = 4, b = 3: 4 Fe + 3 O₂ → 2 Fe₂O₃.

Redox and Charge

With ions, the total charge must match as well: here +17 on both sides. Half-reactions add electrons (e) to make the charges equal.

Example:

Sources & Verification

References

S. S. Zumdahl & S. A. Zumdahl, Chemistry, 10th ed., Cengage Learning, 2018 — Ch. 3 (Balancing chemical equations) and Ch. 18 (Balancing redox equations).
P. Atkins, L. Jones & L. Laverman, Chemical Principles: The Quest for Insight, 7th ed., W. H. Freeman, 2016 — Fundamentals H (Chemical equations) and K (Redox reactions).