Chemical Reactions: Balancing Equations Without Trial and Error

Most students balance equations by guessing coefficients until both sides match. That works for small equations and falls apart on anything with four or more substances. A fixed order is faster.

The order

1. Balance metals first. They usually appear in only one compound on each side.
2. Then non-metals other than hydrogen and oxygen.
3. Then hydrogen.
4. Oxygen last. It appears in the most places, so fixing it last avoids undoing earlier work.

Worked example

For Fe + H₂O → Fe₃O₄ + H₂: balance iron (3 Fe), then hydrogen and oxygen together — four oxygen atoms on the right need 4 H₂O on the left, which gives 8 hydrogen atoms, so 4 H₂ on the right.

3Fe + 4H₂O → Fe₃O₄ + 4H₂

Check

Count every element on both sides once more. If a coefficient is a fraction, multiply everything by the denominator.