Balancing chemical equations step by step, explained simply

This guide is for you if chemical equations look like a puzzle with no rules. In CBSE you balance equations in Class 10 in the chapter Chemical Reactions and Equations, after meeting formulas in Class 9. It is also an early skill in ICSE Class 9 and 10, GCSE and IGCSE chemistry. Once you have a routine, balancing becomes quick and almost mechanical.

The idea in plain words

A chemical equation shows what happens in a reaction:

reactants → products

In a reaction, atoms are rearranged. None are created and none are destroyed. This is the law of conservation of mass. So the number of atoms of each element must be the same on both sides.

An equation where this is true is balanced.

You balance an equation by putting numbers in front of formulas. These are called coefficients.

Part	Example	Can you change it?
Coefficient (big number in front)	the 2 in 2H₂O	Yes
Subscript (small number in a formula)	the 2 in H₂O	No, it changes the substance

A coefficient multiplies everything in the formula after it. So 2H₂O contains 4 hydrogen atoms and 2 oxygen atoms.

A routine that works

1. Write the correct formulas for every reactant and product.
2. Count the atoms of each element on both sides. A small table helps.
3. Pick an element that is unbalanced and add a coefficient to fix it.
4. Recount everything, because one change can unbalance another element.
5. Repeat until every element matches. Leave hydrogen and oxygen until near the end.
6. Make sure the coefficients are in the lowest whole-number ratio.

Worked examples

Example 1: hydrogen and oxygen make water

Unbalanced: H₂ + O₂ → H₂O

Element	Left	Right
H	2	2
O	2	1

1. Oxygen is unbalanced. Put a 2 in front of H₂O: H₂ + O₂ → 2H₂O
2. Recount: O is now 2 and 2. But H on the right is now 4, and on the left it is 2.
3. Put a 2 in front of H₂: 2H₂ + O₂ → 2H₂O
4. Recount: H is 4 and 4, O is 2 and 2.

Balanced: 2H₂ + O₂ → 2H₂O

Example 2: burning methane

Unbalanced: CH₄ + O₂ → CO₂ + H₂O

1. Carbon: 1 on each side. Balanced already.
2. Hydrogen: 4 on the left, 2 on the right. Put a 2 in front of H₂O: CH₄ + O₂ → CO₂ + 2H₂O
3. Oxygen: on the right there are 2 (in CO₂) + 2 (in 2H₂O) = 4. On the left there are 2. Put a 2 in front of O₂: CH₄ + 2O₂ → CO₂ + 2H₂O
4. Final count: C is 1 and 1, H is 4 and 4, O is 4 and 4.

Balanced: CH₄ + 2O₂ → CO₂ + 2H₂O

Example 3: iron and steam

This one appears in the CBSE Class 10 textbook.

Unbalanced: Fe + H₂O → Fe₃O₄ + H₂

1. Iron: 1 on the left, 3 on the right. Put a 3 in front of Fe: 3Fe + H₂O → Fe₃O₄ + H₂
2. Oxygen: 1 on the left, 4 on the right. Put a 4 in front of H₂O: 3Fe + 4H₂O → Fe₃O₄ + H₂
3. Hydrogen: now 8 on the left (4 × 2), and 2 on the right. Put a 4 in front of H₂: 3Fe + 4H₂O → Fe₃O₄ + 4H₂
4. Final count: Fe is 3 and 3, O is 4 and 4, H is 8 and 8.

Balanced: 3Fe + 4H₂O → Fe₃O₄ + 4H₂

With state symbols: 3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)

Example 4: aluminium and oxygen (an odd and even trick)

Unbalanced: Al + O₂ → Al₂O₃

1. Oxygen is 2 on the left and 3 on the right. The lowest common multiple of 2 and 3 is 6.
2. To get 6 oxygen atoms on each side: 3O₂ on the left and 2Al₂O₃ on the right. Al + 3O₂ → 2Al₂O₃
3. Aluminium: now 4 on the right (2 × 2). Put a 4 in front of Al: 4Al + 3O₂ → 2Al₂O₃
4. Final count: Al is 4 and 4, O is 6 and 6.

Balanced: 4Al + 3O₂ → 2Al₂O₃

A shortcut for polyatomic ions

If a group like OH, SO₄ or NO₃ stays together on both sides, count it as one unit.

Ca(OH)₂ + HCl → CaCl₂ + H₂O

Cl is 1 on the left and 2 on the right, so use 2HCl. Then there are 4 H atoms on the left (2 in Ca(OH)₂ and 2 in 2HCl), so use 2H₂O.

Balanced: Ca(OH)₂ + 2HCl → CaCl₂ + 2H₂O

Check: Ca 1 and 1, O 2 and 2, H 4 and 4, Cl 2 and 2.

Common mistakes and how to avoid them

Changing subscripts. Turning H₂O into H₂O₂ to fix oxygen creates a different substance. Only change coefficients.

Forgetting a coefficient multiplies the whole formula. In 3Ca(OH)₂ there are 3 Ca, 6 O and 6 H atoms. The bracket’s subscript and the coefficient both multiply.

Not recounting. Fixing one element often unbalances another, as in Example 1. Recount every element after every change.

Putting a coefficient in the middle of a formula. H₂2O is meaningless. The coefficient always goes in front.

Leaving fractions or a ratio that can be reduced. 4H₂ + 2O₂ → 4H₂O is balanced but not in its simplest form. Divide by 2 to get 2H₂ + O₂ → 2H₂O.

Wrong formulas to begin with. If the formula is wrong, no amount of balancing will fix it. Check valencies first.

Try these

Balance each equation.

1. Mg + O₂ → MgO
2. N₂ + H₂ → NH₃
3. C₃H₈ + O₂ → CO₂ + H₂O
4. Na + H₂O → NaOH + H₂
5. BaCl₂ + Na₂SO₄ → BaSO₄ + NaCl

Answers

1. 2Mg + O₂ → 2MgO (Mg 2 and 2, O 2 and 2)
2. N₂ + 3H₂ → 2NH₃ (N 2 and 2, H 6 and 6)
3. C₃H₈ + 5O₂ → 3CO₂ + 4H₂O (C 3 and 3, H 8 and 8, O 10 and 10)
4. 2Na + 2H₂O → 2NaOH + H₂ (Na 2 and 2, H 4 and 4, O 2 and 2)
5. BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl (Ba 1, SO₄ 1, Na 2 and 2, Cl 2 and 2)

Still unsure?

Balancing gets much easier once formulas and valencies are secure, and that is often where the real gap is. A Qlive teacher can work through it with you one-to-one, starting with a free assessment that finds the exact gap. You can read more about how we teach on our chemistry page, and for the background on elements, see our guide to the periodic table.