How do you balance a chemical equation step by step?

1) Write the correct formulas for all reactants and products. 2) Count the atoms of each element on both sides. 3) Add coefficients (the big numbers in front) so every element has the same atom count on each side — balance metals first, then non-metals, and leave hydrogen and oxygen for last. 4) Reduce the coefficients to the smallest whole-number ratio. Never change a subscript, because that changes the substance itself. For example, H2 + O2 becomes 2H2 + O2 → 2H2O.

What is the difference between a coefficient and a subscript?

A coefficient is the large number written in front of a formula (for example the 2 in 2H2O) and it multiplies the entire molecule. A subscript is the small number inside a formula (the 2 in H2O) and it counts the atoms of one element in a single molecule. You balance an equation by changing coefficients only — changing a subscript would turn the chemical into a different substance.

Why must chemical equations be balanced?

Because of the law of conservation of mass: atoms are never created or destroyed in a chemical reaction, they are only rearranged. A balanced equation guarantees that the number of atoms of each element is identical on the reactant and product sides, so mass is conserved. Balancing also gives the correct mole ratios needed for stoichiometry calculations.

How does this chemical equation balancer work?

Type any equation such as C3H8 + O2 -> CO2 + H2O into the calculator and it returns the balanced equation instantly by solving the atom-conservation equations. In Simulate mode you can also adjust each coefficient by hand and watch a live balance beam tilt until both sides carry the same atoms. Practice and Quiz modes give you unbalanced equations to solve yourself with instant feedback.

How do you balance combustion equations?

For the combustion of a hydrocarbon, balance carbon first (match CO2 to the carbons in the fuel), then hydrogen (match H2O to the hydrogens), and balance oxygen last because it appears in both products. If the oxygen count comes out odd, use a fraction such as 7/2 O2 and then multiply every coefficient by 2. Example: C3H8 + 5O2 → 3CO2 + 4H2O.

Balancing Chemical Equations

Balance any equation instantly, tune coefficients on a live balance beam, and practice with 60+ reactions & a quiz

Mode

Chemical Bonds

Build an Atom 📖 User Guide

⚖ Balance the Equation

Pick a reaction, then use the −/+ steppers to set each coefficient. The beam levels and turns lime when both sides carry the same atoms.

Unbalanced

Choose a reaction by level

Or balance your own equation

User Guide — Balancing Chemical Equations

1 Overview

This tool teaches and checks the balancing of chemical equations. It has four modes: Simulate (hands-on coefficient tuning on a live balance beam, plus an instant balancer for any equation you type), Explore (concept cards on conservation of mass, the balancing method, and reaction types), Practice (fill-in-the-coefficient exercises with instant feedback and hints), and Quiz (5 randomised equations with a star rating). It covers 60+ built-in reactions across synthesis, decomposition, combustion, single- and double-replacement types.

2 Simulate Mode

Pick a reaction from the chips, or keep the default. Every coefficient starts at 1, so the equation begins unbalanced.
Use the − / + steppers under each formula to change its coefficient. The balance beam on the right tilts toward the heavier side and the element table shows the atom count of each element on both sides — green ✓ when an element matches, red ≠ when it does not.
When every element matches, the beam levels, turns lime, and shows ✓ BALANCED.
⚖ Auto-Balance animates the coefficients up to the correct answer. ↻ Reset returns all coefficients to 1.
Balance your own equation: type any equation using -> or = between the two sides (e.g. C3H8 + O2 -> CO2 + H2O) and click Balance for the instant answer. Use Load into simulator to explore it hands-on.
Right-click the canvas for a menu: Auto-Balance, Save as Image, Copy Balanced Equation, or Reset. The speaker icon mutes sounds.

3 Explore Mode

Read concept cards across four tabs: Basics (conservation of mass, coefficient vs subscript, counting atoms), How to Balance (the four-step method — count, metals first, odd/even trick, reduce to lowest terms), Reaction Types (synthesis, decomposition, combustion, replacement with examples), and Tips & Mistakes (never change subscripts, treat polyatomic ions as units, using fractions).

4 Practice & Quiz

Practice: an unbalanced equation appears with a blank box in front of each formula. Type the coefficients and click Check Answer for instant feedback; the running score updates. Stuck? 💡 Hint fills in one correct coefficient for you. Click Next Equation for a fresh one.

Quiz: 5 randomised equations. Type the coefficients and Submit — each answer is marked and the correct balanced equation is shown. The result screen gives a star rating (5/5 = ★★★) and lists every equation with the correct answer to review.

5 Key Concepts & Tips

Only change coefficients (the big numbers in front) — never the subscripts inside a formula.
Balance metals first, then non-metals, and H and O last.
If oxygen comes out odd, use a fraction like 7/2 O₂ then multiply everything by 2.
Reduce every answer to the smallest whole-number ratio — the Practice and Quiz checkers expect lowest terms.
Keep polyatomic ions (SO₄, NO₃, OH) together as a single group when they survive the reaction.

Free Balancing Chemical Equations Calculator & Interactive Simulator

Balancing chemical equations is the first real skill every chemistry student has to master — and the one that trips the most people up. This free tool does both jobs at once: it is an instant equation balancer (type an equation, get the balanced answer) and an interactive simulator where you set the coefficients yourself and watch a live balance beam tilt until the two sides carry exactly the same atoms. No login, no download, works on any phone, tablet, or laptop.

What Does It Mean to Balance a Chemical Equation?

A chemical equation is balanced when every element has the same number of atoms on the reactant side and the product side. This is required by the law of conservation of mass: atoms are never created or destroyed in a reaction, they are only rearranged. You balance an equation by placing coefficients (the large numbers in front of each formula) — and only coefficients. Consider the formation of water:

H₂ + O₂ → H₂O (unbalanced) ⟶ 2H₂ + O₂ → 2H₂O (balanced)

Coefficient vs Subscript — The Rule You Cannot Break

The single most important rule: you may change coefficients, but never subscripts. A coefficient multiplies the whole molecule (the 2 in 2H₂O means two water molecules). A subscript counts atoms inside one molecule (the 2 in H₂O means two hydrogen atoms per molecule). Changing the subscript in H₂O to make H₂O₂ does balance the arithmetic — but it turns water into hydrogen peroxide, a completely different chemical. The simulator only lets you touch coefficients, so it builds the correct habit automatically.

How to Balance a Chemical Equation Step by Step

Step	What to do
1. Count	List each element and its atom count on both sides (the tool's live table does this for you).
2. Metals first	Balance elements that appear in only one compound per side — usually metals, then other non-metals.
3. H and O last	Leave hydrogen and oxygen until the end because they appear in many compounds. Use a fraction if oxygen is odd.
4. Reduce	Divide all coefficients by their greatest common factor so the ratio is the smallest whole numbers.

Worked Example — Combustion of Propane

Take C₃H₈ + O₂ → CO₂ + H₂O. Balance carbon first: 3 carbons in propane means 3 CO₂. Balance hydrogen next: 8 hydrogens means 4 H₂O. Now count oxygen on the right: 3×2 + 4×1 = 10, so we need 5 O₂ on the left. The balanced equation is C₃H₈ + 5O₂ → 3CO₂ + 4H₂O. Load it into the simulator and step the coefficients to see the beam level out.

The Five Reaction Types You Will Balance

The built-in library groups its 60+ reactions by type so you can drill each pattern: synthesis (A + B → AB, e.g. N₂ + 3H₂ → 2NH₃), decomposition (AB → A + B, e.g. 2H₂O₂ → 2H₂O + O₂), combustion (fuel + O₂ → CO₂ + H₂O), single replacement (A + BC → AC + B, e.g. Zn + 2HCl → ZnCl₂ + H₂), and double replacement (AB + CD → AD + CB, e.g. AgNO₃ + NaCl → AgCl + NaNO₃). Recognising the type often tells you where to start balancing.

Why Use an Interactive Balancer Instead of Just an Answer?

A plain calculator hands you the answer but teaches nothing. Here the balance-beam animation and per-element atom table make conservation of mass visible: raise a coefficient and you watch atoms pile onto one pan while the table flips a red ≠ to a green ✓. Students remember what they see move. Teachers can project the canvas as a live demonstration, and learners can self-test in Practice and Quiz mode until balancing becomes automatic.

Who Uses This Chemistry Simulator?

Students preparing for GCSE, IGCSE, A-Level, AP, IB, and vocational (BTEC/TVET) chemistry use it to master balancing before stoichiometry. Teachers and tutors use the live canvas as a classroom demonstration and the Practice/Quiz modes as instant, self-marking homework. Self-learners and adult learners returning to chemistry use the instant balancer to check homework and the Explore cards to relearn the method. The tool is completely free, needs no account, and runs entirely in the browser.

Explore Related Free Chemistry & Science Simulators

Build on what you learn here with other free simulators on MechSimulator. See how atoms actually join with the Chemical Bonds Simulator, construct elements electron-by-electron in the Build an Atom Simulator, and test acids and alkalis with the Litmus Paper Test Virtual Lab. Explore gas behaviour with the Ideal Gas Law Simulator, or model reacting mixtures with the Acids & Bases Mixing Simulator. All tools are free, browser-based, and require no signup or installation.

Balancing Equations Quiz