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Chemical Equation Balancer

Balance chemical equations instantly with step-by-step working for UK GCSE and A-Level Chemistry

Balance Your Equation

Use arrow (-> or =) to separate reactants and products. Use numbers after element symbols for subscripts.

Quick examples:
BALANCED EQUATION
Step-by-step working:

Reference: 50 Common Balanced Equations

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Balanced EquationReaction TypeTopic

How to Balance Chemical Equations: A Complete GCSE Guide

Balancing chemical equations is one of the most fundamental skills in chemistry. It is based on the law of conservation of mass, which states that atoms cannot be created or destroyed during a chemical reaction. Our chemical equation balancer instantly balances equations for you and shows the step-by-step working, making it ideal for UK GCSE and A-Level Chemistry revision.

The Law of Conservation of Mass

Antoine Lavoisier established the law of conservation of mass in 1789. In any chemical reaction, the total mass of the reactants always equals the total mass of the products. This means the number of each type of atom must be the same on both sides of the chemical equation. When an equation satisfies this condition, it is said to be balanced.

For example, the unbalanced equation H2 + O2 → H2O shows 2 hydrogen atoms and 2 oxygen atoms on the left, but only 2 hydrogen atoms and 1 oxygen atom on the right. By adjusting coefficients to get 2H2 + O2 → 2H2O, we achieve 4 hydrogen atoms and 2 oxygen atoms on each side.

Step-by-Step Method for Balancing Equations

  1. Write the unbalanced equation with correct chemical formulas for all reactants and products.
  2. Count the atoms of each element on both sides of the arrow.
  3. Balance the most complex molecule first - usually the one with the most elements.
  4. Balance metals next, then non-metals, leaving hydrogen and oxygen until last.
  5. Adjust coefficients (never subscripts) until each element is balanced.
  6. Check your work by counting all atoms on both sides again.
  7. Add state symbols (s), (l), (g), (aq) if required.

Types of Chemical Reactions

Understanding the type of reaction helps predict products and balance equations more efficiently:

  • Combustion: A fuel reacts with oxygen to produce carbon dioxide and water. Example: CH4 + 2O2 → CO2 + 2H2O
  • Decomposition: One compound breaks down into simpler substances. Example: 2H2O2 → 2H2O + O2
  • Neutralisation: An acid reacts with a base to form a salt and water. Example: HCl + NaOH → NaCl + H2O
  • Displacement: A more reactive element displaces a less reactive one. Example: Fe + CuSO4 → FeSO4 + Cu
  • Precipitation: Two solutions react to form an insoluble solid. Example: AgNO3 + NaCl → AgCl + NaNO3
  • Redox: Simultaneous oxidation and reduction reactions occur with electron transfer.

State Symbols in Chemical Equations

State symbols provide important information about the physical state of each substance:

  • (s) Solid - e.g. NaCl(s), Fe(s)
  • (l) Liquid - e.g. H2O(l), Br2(l)
  • (g) Gas - e.g. CO2(g), H2(g)
  • (aq) Aqueous solution - e.g. HCl(aq), NaOH(aq)

State symbols are required for full marks in many GCSE and A-Level Chemistry examinations. They help describe the physical conditions under which the reaction takes place.

Reactants and Products

In a chemical equation, the substances on the left of the arrow are called reactants - these are the starting materials that are consumed during the reaction. The substances on the right are called products - these are the new substances formed. The arrow represents the chemical change taking place. In reversible reactions, a double arrow (⇌) is used to show that the reaction can proceed in both directions.

Coefficients and Mole Ratios

The coefficients in a balanced equation are the numbers placed in front of chemical formulas. They represent the relative number of moles (or molecules) of each substance involved. For instance, in 2H2 + O2 → 2H2O, the coefficient 2 in front of H2 means 2 moles of hydrogen react with 1 mole of oxygen to produce 2 moles of water. These ratios are essential for all stoichiometry calculations including theoretical yield, limiting reagent, and atom economy.

Atom Economy

Atom economy is a measure of how efficiently atoms from reactants end up in the desired product. It is calculated as:

Atom Economy = (Molecular mass of desired product / Total molecular mass of all products) × 100%

A high atom economy means fewer waste products and is an important consideration in green chemistry. The Haber process for ammonia synthesis (N2 + 3H2 → 2NH3) has a 100% atom economy as ammonia is the only product.

Important Industrial Reactions

Several industrial processes have balanced equations that are critical for GCSE and A-Level study:

  • Haber Process: N2(g) + 3H2(g) ⇌ 2NH3(g) - produces ammonia for fertilisers
  • Contact Process: 2SO2(g) + O2(g) ⇌ 2SO3(g) - makes sulfuric acid
  • Thermal Decomposition of Limestone: CaCO3(s) → CaO(s) + CO2(g) - cement production
  • Electrolysis of Brine: 2NaCl(aq) + 2H2O(l) → Cl2(g) + H2(g) + 2NaOH(aq) - chlor-alkali industry
  • Blast Furnace: Fe2O3(s) + 3CO(g) → 2Fe(l) + 3CO2(g) - iron extraction

Frequently Asked Questions

How do you balance a chemical equation?

To balance a chemical equation, adjust the coefficients (numbers in front of formulas) so that the number of atoms of each element is equal on both sides. Never change the subscripts within chemical formulas. Work systematically: start with the most complex molecule, balance metals first, then non-metals, and leave H and O until last. Verify by counting all atoms on both sides.

What is the law of conservation of mass?

The law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction. The total mass of reactants must equal the total mass of products. This is why chemical equations must be balanced - the same number of each type of atom must appear on both sides. This fundamental law underpins all stoichiometry in GCSE and A-Level Chemistry.

What do state symbols mean in chemical equations?

State symbols indicate the physical state of each substance: (s) = solid, (l) = liquid, (g) = gas, and (aq) = aqueous solution. For example, NaCl(s) + H2O(l) shows solid sodium chloride reacting with liquid water. State symbols are often required for full marks in GCSE Chemistry exam questions.

What is the difference between a word equation and a symbol equation?

A word equation uses the full names of substances (e.g. hydrogen + oxygen → water), while a symbol equation uses chemical formulas (e.g. 2H2 + O2 → 2H2O). Symbol equations provide more detail, showing exact atomic ratios. Balanced symbol equations are essential for quantitative chemistry calculations including molar mass, yield, and concentration.

What is the mole ratio in a balanced equation?

The coefficients in a balanced equation give the mole ratio of reactants to products. In 2H2 + O2 → 2H2O, the ratio is 2:1:2. This means 2 moles of hydrogen react with 1 mole of oxygen to produce 2 moles of water. Mole ratios are essential for calculating theoretical yield, limiting reagent, and atom economy.

How do you balance ionic equations?

Write the full balanced equation, then split all soluble ionic compounds into their separate ions. Cancel out spectator ions (those unchanged on both sides). The result is the net ionic equation. For example, Ag+(aq) + Cl-(aq) → AgCl(s) for the precipitation of silver chloride. Both charge and atoms must balance in ionic equations.

What are half equations in redox chemistry?

Half equations show either oxidation or reduction separately, including electrons (e-). In the electrolysis of copper sulfate, the cathode half equation is: Cu2+ + 2e- → Cu (reduction). The anode half equation is: 2H2O → O2 + 4H+ + 4e- (oxidation). Adding the two half equations together gives the overall redox equation, with electrons cancelling out.

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Mustafa Bilgic
Chemistry & Science Calculator Specialist at UK Calculator. Focused on building accurate, curriculum-aligned tools for UK GCSE and A-Level students.
Last updated: February 2026

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