Chemical Equation Balancer
Balance common chemical equations for school and college chemistry.
How to balance chemical equations
Balancing a chemical equation means adjusting coefficients so that the number of atoms of each element is equal on both sides (law of conservation of mass). Only coefficients can be changed — never subscripts.
Write the unbalanced equation with reactants on the left and products on the right, separated by an arrow.
Count the number of atoms of each element on both sides of the equation.
Add whole-number coefficients before formulas to make atom counts equal on both sides. Reduce to lowest whole numbers.
Frequently asked questions
Why must chemical equations be balanced?
According to the Law of Conservation of Mass (Lavoisier, 1789), matter cannot be created or destroyed in a chemical reaction. The total mass of reactants must equal the total mass of products. A balanced equation ensures the same number of each type of atom appears on both sides.
Can I change subscripts to balance equations?
No. Changing subscripts changes the chemical formula itself — it would make a different compound. For example, H₂O (water) and H₂O₂ (hydrogen peroxide) are completely different substances. Only coefficients (the big numbers before formulas) may be changed.
What is the difference between a coefficient and a subscript?
A coefficient is the number placed before a chemical formula (e.g., 2H₂O means 2 molecules of water = 4 hydrogen atoms and 2 oxygen atoms). A subscript is the small number within the formula (e.g., in H₂O, the "2" means 2 hydrogen atoms per molecule). Only coefficients change during balancing.
What is the Haber process?
The Haber process (N₂ + 3H₂ → 2NH₃) is the industrial synthesis of ammonia from nitrogen and hydrogen gas. Developed by Fritz Haber in 1909, it is one of the most important industrial reactions, producing fertilizer that feeds roughly half the world's population.
What is oxidation and reduction in redox reactions?
Oxidation is the loss of electrons (and usually gain of oxygen or loss of hydrogen). Reduction is the gain of electrons. In redox reactions, oxidation and reduction always occur simultaneously — one species loses electrons while another gains them. OIL RIG is a useful mnemonic: Oxidation Is Loss, Reduction Is Gain.