NCERT Class 10 Science — Chapter 1, Chemical Reactions and Equations

How do you balance a chemical equation step by step?

Count the atoms of each element on both sides, then adjust the coefficients in front of the formulas until every count matches. Never change a subscript: that rewrites the substance itself. Balance the element appearing in the fewest compounds first, and leave hydrogen and oxygen until last.

Coefficients change amounts; subscripts change substances

This is the whole idea, and it is the one thing worth being absolutely firm about. The 2 in 2H₂O means two water molecules. The small 2 in H₂O means each molecule contains two hydrogen atoms. Changing the first is balancing; changing the second turns water into something that is not water.

A balanced equation is a statement that atoms are conserved — nothing is created or destroyed, only rearranged. If your equation balances only after you have edited a subscript, you have not balanced a reaction, you have invented a different one.

An order that avoids going round in circles

Start with the element that appears in the fewest compounds, because changing its coefficient disturbs the least. Leave hydrogen and oxygen for last: they turn up almost everywhere, so balancing them early means re-balancing them repeatedly.

If you end up needing a fraction, that is fine as a working step — multiply the whole equation through at the end to clear it. Examiners expect the final answer in the smallest whole-number ratio.

A worked example

Balance the reaction between iron and steam: Fe + H₂O → Fe₃O₄ + H₂

  1. Write the equation and count each element
    atoms must match on both sides
    Fe: 1 vs 3 H: 2 vs 2 O: 1 vs 4
  2. Balance iron first — it appears in the fewest compounds
    Fe on the right is locked at 3 by Fe₃O₄
    put a 3 in front of Fe on the left
  3. Now oxygen
    Fe₃O₄ needs 4 oxygen atoms
    4 H₂O supplies exactly 4 oxygen
  4. Hydrogen falls out last
    4 H₂O carries 8 hydrogen atoms
    4 H₂ on the right accounts for all 8 — the equation balances

⚙️ Every number above was computed by Bolo’s Equation Balancer engine when this page was built — the same code that checks your answer inside the app, not a hand-typed solution.

Now try it yourself

Reading a solution is the easy half. In the Equation Balancer you set the values and the engine checks each step — and if you get stuck it shows you the method before it shows the answer.

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Common questions

Why can't you change the subscripts to balance an equation?

Because subscripts define what the substance is. Changing H₂O to H₂O₂ does not balance water, it replaces water with hydrogen peroxide — a different compound with different properties. Coefficients change how many molecules react; subscripts change which molecules they are.

Which element should you balance first?

The one appearing in the fewest compounds, because adjusting it disturbs the least elsewhere. Leave hydrogen and oxygen until last, since they appear in almost everything and balancing them early usually means having to redo them after every other change.

Can coefficients be fractions?

As a working step, yes, and it often makes the algebra easier. But the final answer should be in the smallest whole-number ratio, so multiply every coefficient through by the denominator once the equation balances. Examiners expect whole numbers in the final line.