Balanced equation

A balanced equation is a chemical equation in which the number of atoms of each element is equal on both sides. This is achieved by placing coefficients in front of the formulae, without changing any formula itself. Malay: persamaan seimbang · Chinese: 配平方程式.

Balancing is required because atoms are neither created nor destroyed in a chemical reaction; they are only rearranged, so the same atoms must appear on both sides. You balance by adjusting the big numbers in front of each formula until every element has an equal count of atoms on the left and the right of the arrow.

Example. The reaction of hydrogen with oxygen is written 2H₂ + O₂ → 2H₂O. On each side there are four hydrogen atoms and two oxygen atoms, so the equation is balanced. Without the coefficients, H₂ + O₂ → H₂O would have two oxygen atoms on the left but only one on the right, so it would not balance. As a second case, the burning of methane balances as CH₄ + 2O₂ → CO₂ + 2H₂O, with one carbon, four hydrogen and four oxygen atoms on each side.

Confusion to avoid. You may only change the coefficients, never the subscripts inside a formula, because changing a subscript would turn the substance into something else. A common error is to write H₂O as H₂O₂ to balance oxygen, which is wrong. Take care too to distinguish a balanced equation from a word equation, which names the substances but does not show the atom counts.

In this chapter the balanced equation is essential because its coefficients give the mole ratio, which is the key to every stoichiometry calculation, so learning to balance reliably underpins much of SPM Chemistry.