Chemical Equation Balancer – Balance Chemical Reactions

Balance any chemical equation with our free online equation balancer. Get balanced equations with coefficients and step-by-step solutions for chemistry homework and stoichiometry calculations.

Chemical Equation

Use -> or → for arrow. Example: CH4 + O2 -> CO2 + H2O

Understanding Chemical Equation Balancing

Chemical equations represent reactions, showing what substances react (reactants) and what substances form (products). But an equation isn't complete until it's balanced – meaning the same number of atoms of each element appears on both sides. This reflects the law of conservation of mass: matter cannot be created or destroyed in a chemical reaction.

Balancing works by adjusting coefficients – the numbers in front of chemical formulas. You never change the subscripts within formulas (that would change the substance itself). The goal is finding the smallest whole-number coefficients that make atom counts equal on both sides.

How to Balance Chemical Equations

1
Write the unbalanced equation
List reactants on the left, products on the right, separated by an arrow. Use correct chemical formulas.
2
Count atoms of each element
List how many atoms of each element appear on both sides. Remember: subscripts multiply, coefficients multiply everything in the formula.
3
Add coefficients to balance
Start with elements that appear in only one compound on each side. Save hydrogen and oxygen for last. Adjust coefficients until counts match.
4
Simplify coefficients
Reduce to the smallest whole numbers. If all coefficients are divisible by 2, divide them. Check that all atom counts still balance.

Worked Examples

Example 1: Water Formation (H₂ + O₂ → H₂O)

Unbalanced: H₂ + O₂ → H₂O

Count: Left has 2 H, 2 O. Right has 2 H, 1 O.

Balance oxygen: H₂ + O₂ → 2H₂O (now 2 O on right)

Balance hydrogen: 2H₂ + O₂ → 2H₂O (now 4 H on both sides)

Balanced: 2H₂ + O₂ → 2H₂O

Two molecules of hydrogen react with one molecule of oxygen to form two molecules of water.

Example 2: Methane Combustion (CH₄ + O₂ → CO₂ + H₂O)

Unbalanced: CH₄ + O₂ → CO₂ + H₂O

Balance C: Already balanced (1 on each side)

Balance H: CH₄ + O₂ → CO₂ + 2H₂O (4 H on each side)

Balance O: CH₄ + 2O₂ → CO₂ + 2H₂O (4 O on each side)

Balanced: CH₄ + 2O₂ → CO₂ + 2H₂O

Complete combustion of methane produces carbon dioxide and water. This is the reaction in natural gas burning.

Example 3: Rust Formation (Fe + O₂ → Fe₂O₃)

Unbalanced: Fe + O₂ → Fe₂O₃

Balance Fe: 2Fe + O₂ → Fe₂O₃

Balance O: Need 3 O on left, but O₂ comes in pairs

Use fraction: 2Fe + 1.5O₂ → Fe₂O₃

Multiply by 2: 4Fe + 3O₂ → 2Fe₂O₃

Balanced: 4Fe + 3O₂ → 2Fe₂O₃

Iron rusting requires oxygen from air. The balanced equation shows 4 iron atoms react with 3 oxygen molecules.

Example 4: Photosynthesis (C₆H₁₂O₆ + O₂ → CO₂ + H₂O)

Actually, photosynthesis is: CO₂ + H₂O → C₆H₁₂O₆ + O₂

Balance C: 6CO₂ + H₂O → C₆H₁₂O₆ + O₂

Balance H: 6CO₂ + 6H₂O → C₆H₁₂O₆ + O₂

Balance O: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Balanced: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Plants use sunlight to convert carbon dioxide and water into glucose and oxygen. This reaction sustains life on Earth.

Example 5: Ammonia Synthesis (N₂ + H₂ → NH₃)

Unbalanced: N₂ + H₂ → NH₃

Balance N: N₂ + H₂ → 2NH₃ (2 N on each side)

Balance H: N₂ + 3H₂ → 2NH₃ (6 H on each side)

Balanced: N₂ + 3H₂ → 2NH₃

The Haber process produces ammonia from nitrogen and hydrogen. This reaction is crucial for fertilizer production.

Example 6: Complex Equation (Ca(OH)₂ + H₃PO₄ → Ca₃(PO₄)₂ + H₂O)

Balance Ca: 3Ca(OH)₂ + H₃PO₄ → Ca₃(PO₄)₂ + H₂O

Balance PO₄: 3Ca(OH)₂ + 2H₃PO₄ → Ca₃(PO₄)₂ + H₂O

Balance H: 3Ca(OH)₂ + 2H₃PO₄ → Ca₃(PO₄)₂ + 6H₂O

Check O: 6 + 8 = 14 on left, 8 + 6 = 14 on right ✓

Balanced: 3Ca(OH)₂ + 2H₃PO₄ → Ca₃(PO₄)₂ + 6H₂O

This acid-base reaction forms calcium phosphate (a precipitate) and water. Parentheses in formulas mean the subscript applies to everything inside.

Quick Fact

Antoine Lavoisier established the law of conservation of mass in 1789. His careful measurements showed that matter is neither created nor destroyed in chemical reactions. This fundamental principle is why we balance equations – the atoms present at the start must all be present at the end, just rearranged into different compounds.

Frequently Asked Questions

Why must chemical equations be balanced?

Balanced equations obey the law of conservation of mass. Atoms aren't created or destroyed in chemical reactions – they just rearrange. An unbalanced equation would imply atoms appear or disappear, which violates fundamental physics.

Can I change subscripts to balance equations?

Never. Changing subscripts changes the chemical identity of the substance. H₂O is water; H₂O₂ is hydrogen peroxide (very different!). Only coefficients (numbers in front) can be changed when balancing.

What do the coefficients mean?

Coefficients represent the mole ratio of reactants and products. In 2H₂ + O₂ → 2H₂O, two moles of hydrogen react with one mole of oxygen to produce two moles of water.

What if I get fractional coefficients?

Fractions are mathematically correct but conventionally we use whole numbers. Multiply all coefficients by the denominator to eliminate fractions. For example, if you get 1, 1.5, 1, multiply by 2 to get 2, 3, 2.

How do I handle polyatomic ions?

If a polyatomic ion (like SO₄²⁻ or NO₃⁻) appears unchanged on both sides, treat it as a unit. Balance the ion as a whole rather than counting individual atoms within it.

What's the inspection method for balancing?

Inspection means balancing by trial and error, adjusting coefficients until counts match. Start with complex molecules, save simple elements (like O₂) for last. For difficult equations, use the algebraic method with variables.

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