Conservation in chemical equations — Chemistry, 14–17 years
A reaction rearranges atoms rather than making them vanish. Balanced equations show the same number of each kind of atom before and after the change.
Atoms are rearranged
In a chemical reaction, old bonds break and new bonds form, but the atoms themselves are not created or destroyed. A chemical equation is balanced when both sides contain equal numbers of each element, even though the substances have changed.
Why balance equations
Early chemists needed to check whether their measurements made sense and to calculate how much reactant a reaction would need. Balancing is that check: it prevents a chemical recipe from quietly inventing or losing atoms.
Balancing hydrogen burning
Begin with H₂ + O₂ → H₂O. Put 2 before H₂O: now there are two O atoms on the right. Put 2 before H₂: both sides now have four H atoms and two O atoms. The balanced equation is 2H₂ + O₂ → 2H₂O.
Change coefficients, not formulas
A tempting shortcut is to alter H₂O into H₂O₂ so the numbers match. It seems reasonable because the small numbers are visible, but that changes water into hydrogen peroxide, a different substance. Balance by placing whole-number coefficients in front of formulas.
Planning real reactions
Engineers use balanced equations to estimate fuel, oxygen and raw materials in engines, factories and water treatment. The calculation is a starting model: temperature, purity and incomplete reactions can make the measured result different.
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