Use uppercase symbols and numbers (e.g., NaCl, H2SO4).
Balanced Result
Calculation Error
Chemical Equation Types
Explore common chemical reactions and balance them instantly.
Combination / Synthesis
Two or more substances combine to form one product.
H2 + O2 = H2O
2H2 + O2 = 2H2O
Decomposition
A single compound breaks down into two or more elements or new compounds.
H2O = H2 + O2
2H2O = 2H2 + O2
Single Displacement
An element reacts with a compound and takes the place of another element.
Zn + HCl = ZnCl2 + H2
Zn + 2HCl = ZnCl2 + H2
Double Displacement
Two compounds react, and the ions of the two reactants switch places.
AgNO3 + NaCl = AgCl + NaNO3
AgNO3 + NaCl = AgCl + NaNO3
Combustion
A substance reacts with oxygen gas, releasing energy in the form of light and heat.
CH4 + O2 = CO2 + H2O
CH4 + 2O2 = CO2 + 2H2O
Acid + Base / Neutralization
An acid and a base react to form a salt and water.
H2SO4 + NaOH = Na2SO4 + H2O
H2SO4 + 2NaOH = Na2SO4 + 2H2O
Redox
A reaction involving the transfer of electrons between two species.
Fe + O2 = Fe2O3
4Fe + 3O2 = 2Fe2O3
Metal + Acid
A reactive metal displaces hydrogen from an acid.
Mg + HCl = MgCl2 + H2
Mg + 2HCl = MgCl2 + H2
Metal + Water
A metal reacts with water to produce a metal hydroxide and hydrogen gas.
Na + H2O = NaOH + H2
2Na + 2H2O = 2NaOH + H2
Precipitation
Two aqueous solutions combine to form a solid precipitate.
BaCl2 + Na2SO4 = BaSO4 + NaCl
BaCl2 + Na2SO4 = BaSO4 + 2NaCl
Conservation of Mass: Equal Atoms on Both Sides
Balancing a chemical equation is rooted in the Law of Conservation of Mass, formulated by Antoine Lavoisier. In an ordinary chemical reaction, matter is neither created nor destroyed. The bonds holding molecules together break, and individual atoms reorganize into new substances, but every single atom entering the reaction must remain accounted for when the reaction concludes.
When an unbalanced equation such as H2 + O2 → H2O is written, it appears that an oxygen atom has vanished. Balancing resolves this discrepancy by determining the lowest whole-number stoichiometric coefficients needed so that every element has an identical atom count on both sides: 2H2 + O2 → 2H2O.
| Element | Reactants | Products | Balance |
|---|---|---|---|
| Hydrogen (H) | 2 × 2 = 4 | 2 × 2 = 4 | ✓ Equal |
| Oxygen (O) | 1 × 2 = 2 | 2 × 1 = 2 | ✓ Equal |
Multiplies the entire molecular quantity. You have two molecules of water, retaining its chemical identity.
Changes the compound itself. H&sub2;O is water; H&sub2;O&sub2; is hydrogen peroxide, a completely different reactive oxidizing agent.
Change Coefficients, Never Chemical Subscripts
A common mistake when beginning chemistry calculations is altering the small subscript numbers inside chemical formulas to make atom totals match. Subscripts define the fixed atomic ratio that gives a specific compound its unique molecular structure and physical properties.
To balance an equation correctly, you place stoichiometric coefficients directly in front of the chemical formulas. A coefficient scales the entire molecule proportionally without modifying the chemical bonding within it. If no number is shown in front of a formula, the implicit coefficient is 1.
What a Balanced Equation Does Not Predict
Balancing calculates stoichiometric mass proportions, but chemistry requires understanding thermodynamic and physical realities.
Thermodynamic Feasibility
A mathematically balanced equation does not prove a reaction will spontaneously occur. Spontaneity depends on Gibbs free energy (ΔG) and enthalpy change.
Reaction Velocity & Kinetics
Coefficients tell you the mole ratios, not the speed. A reaction might complete in fractions of a second or require decades of slow atmospheric degradation.
Operating Conditions
Many synthesis reactions require specific catalysts, extreme temperatures, or elevated atmospheric pressures (such as the Haber-Bosch ammonia process) to initiate.
Equilibrium & Yield
Reactions rarely proceed to 100% stoichiometric yield in a closed system. Reversible reactions reach chemical equilibrium where forward and reverse rates balance.