Chemical Equation Balancer
Balance chemical equations instantly. Enter an unbalanced equation using the format "Reactants -> Products" and get the balanced equation with coefficients. Supports combustion, combination, decomposition, single replacement, double replacement, and neutralization reactions. See also our Stoichiometry Calculator and Molar Mass Calculator.
Use + between compounds and -> for the reaction arrow
How to Balance Chemical Equations
Balancing chemical equations is a fundamental skill in chemistry that ensures the law of conservation of mass is satisfied. In a balanced equation, the number of atoms of each element on the reactant side equals the number on the product side. No atoms are created or destroyed in a chemical reaction — they are simply rearranged.
The process of balancing equations involves adjusting the coefficients (the numbers in front of chemical formulas) until atom counts match on both sides. You should never change the subscripts within a formula, as that would change the identity of the substance. Systematic approaches include inspection (trial and error), the algebraic method, and the oxidation number method for redox reactions.
- Write the unbalanced equation with correct formulas for all reactants and products
- Count the atoms of each element on both sides
- Start balancing with the most complex molecule or the element that appears in fewest compounds
- Balance metals first, then non-metals, then hydrogen, and finally oxygen
- Use fractional coefficients if needed, then multiply all coefficients to get whole numbers
- Verify that all elements are balanced and coefficients are in lowest terms
Balancing Methods
Inspection Method (Trial and Error):
1. Pick the most complex compound
2. Balance one element at a time
3. Adjust coefficients iteratively
Algebraic Method:
1. Assign variables (a, b, c...) as coefficients
2. Write equations for each element
3. Set one variable = 1, solve the system
4. Multiply to get smallest whole numbers
Example: Fe + O₂ → Fe₂O₃
Fe: a = 2c → a = 2c
O: 2b = 3c → b = 3c/2
Let c = 2: a = 4, b = 3, c = 2
Result: 4Fe + 3O₂ → 2Fe₂O₃ ✓
Example
Problem: Balance the equation: C₃H₈ + O₂ → CO₂ + H₂O
Step 1: Count atoms — Left: 3C, 8H, 2O | Right: 1C, 2H, 3O
Step 2: Balance C: put 3 before CO₂ → C₃H₈ + O₂ → 3CO₂ + H₂O
Step 3: Balance H: put 4 before H₂O → C₃H₈ + O₂ → 3CO₂ + 4H₂O
Step 4: Count O on right: 3(2) + 4(1) = 10 oxygen atoms
Step 5: Balance O: 10/2 = 5 before O₂ → C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
Verify: Left: 3C, 8H, 10O | Right: 3C, 8H, 10O ✓
Supported Reactions Reference Table
| Unbalanced | Balanced | Type |
|---|---|---|
| Fe + O2 -> Fe2O3 | 4Fe + 3O₂ → 2Fe₂O₃ | Combination |
| H2 + O2 -> H2O | 2H₂ + O₂ → 2H₂O | Combination |
| N2 + H2 -> NH3 | N₂ + 3H₂ → 2NH₃ | Combination |
| CH4 + O2 -> CO2 + H2O | CH₄ + 2O₂ → CO₂ + 2H₂O | Combustion |
| C2H6 + O2 -> CO2 + H2O | 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O | Combustion |
| C3H8 + O2 -> CO2 + H2O | C₃H₈ + 5O₂ → 3CO₂ + 4H₂O | Combustion |
| C6H12O6 + O2 -> CO2 + H2O | C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O | Combustion |
| NaOH + HCl -> NaCl + H2O | NaOH + HCl → NaCl + H₂O | Neutralization |
| H2SO4 + NaOH -> Na2SO4 + H2O | H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O | Neutralization |
| KOH + H2SO4 -> K2SO4 + H2O | 2KOH + H₂SO₄ → K₂SO₄ + 2H₂O | Neutralization |
| Zn + HCl -> ZnCl2 + H2 | Zn + 2HCl → ZnCl₂ + H₂ | Single Replacement |
| Fe + CuSO4 -> FeSO4 + Cu | Fe + CuSO₄ → FeSO₄ + Cu | Single Replacement |
Types of Chemical Reactions
Combination (Synthesis): Two or more substances combine to form a single product. General form: A + B → AB. Example: 2Na + Cl₂ → 2NaCl. These reactions often release energy and are common in forming compounds from elements.
Decomposition: A single compound breaks down into two or more simpler substances. General form: AB → A + B. Example: 2KClO₃ → 2KCl + 3O₂. These reactions typically require energy input (heat, electricity, or light) to proceed.
Single Replacement: An element replaces another element in a compound. General form: A + BC → AC + B. Example: Zn + 2HCl → ZnCl₂ + H₂. The activity series determines which metals can replace others.
Double Replacement: Two compounds exchange ions to form two new compounds. General form: AB + CD → AD + CB. Example: AgNO₃ + NaCl → AgCl + NaNO₃. These occur when a precipitate, gas, or water is formed.
Combustion: A substance reacts with oxygen, producing heat and light. Hydrocarbons produce CO₂ and H₂O. Example: CH₄ + 2O₂ → CO₂ + 2H₂O. Complete combustion requires excess oxygen; incomplete combustion produces CO or soot.
Why Balancing Equations Matters
Balanced equations are essential for stoichiometric calculations — determining how much reactant is needed or how much product will form. Without balanced equations, it is impossible to correctly calculate mole ratios, theoretical yields, or limiting reagents. Every quantitative problem in chemistry begins with a balanced equation.
In industrial chemistry, balanced equations determine the proportions of raw materials needed for manufacturing processes. In environmental science, they help track pollutant formation and design remediation strategies. In biochemistry, balanced equations describe metabolic pathways and energy production in living organisms.
Frequently Asked Questions
Why must chemical equations be balanced?
Chemical equations must be balanced to satisfy the law of conservation of mass — matter cannot be created or destroyed in a chemical reaction. The same number of atoms of each element must appear on both sides of the equation. Unbalanced equations violate this fundamental law of nature.
What is a coefficient in a chemical equation?
A coefficient is the number placed before a chemical formula that indicates how many molecules or formula units of that substance participate in the reaction. For example, in 2H₂O, the coefficient 2 means two molecules of water. Coefficients multiply all atoms in the formula.
Can I change subscripts to balance an equation?
No. Changing subscripts changes the identity of the substance. H₂O is water, but H₂O₂ is hydrogen peroxide — a completely different compound. You may only adjust coefficients (the numbers in front of formulas) when balancing equations.
What is the easiest element to balance last?
Oxygen and hydrogen are typically balanced last because they appear in many compounds. Start with metals and unique elements, then balance polyatomic ions as groups if they appear unchanged on both sides, then hydrogen, and finally oxygen.
How do I balance redox equations?
Redox equations are balanced using the half-reaction method: (1) separate into oxidation and reduction half-reactions, (2) balance atoms other than O and H, (3) balance O with H₂O, (4) balance H with H⁺, (5) balance charge with electrons, (6) equalize electrons and add half-reactions.
What does the arrow mean in a chemical equation?
The arrow (→) means "yields" or "produces" and separates reactants (left) from products (right). A double arrow (⇌) indicates a reversible reaction at equilibrium. Conditions like temperature, pressure, or catalysts are sometimes written above or below the arrow.