How do you balance a chemical equation?

Balancing a chemical equation means making sure the number of atoms of each element is the same on both sides of the equation, because matter is neither created nor destroyed in a reaction (Law of Conservation of Mass).

Here’s a step-by-step method:

Steps to Balance a Chemical Equation

1. Write the unbalanced equation
   • Example: H2+O2→H2OH_2 + O_2 → H_2O
2. List the number of atoms of each element on both sides.
   • Left: H = 2, O = 2
   • Right: H = 2, O = 1
3. Balance one element at a time
   • To balance O, place coefficient 2 before H₂O: H2+O2→2H2OH_2 + O_2 → 2H_2O
   • Now Left: H = 2, O = 2
     Right: H = 4, O = 2
4. Balance hydrogen next
   • Put coefficient 2 before H₂: 2H2+O2→2H2O2H_2 + O_2 → 2H_2O
   • Left: H = 4, O = 2
     Right: H = 4, O = 2
5. Check all elements
   • Both sides have equal numbers of H and O.
   • The equation is now balanced.

Tips

• Only change coefficients (the big numbers in front), never subscripts (the small numbers in formulas).
• Start with the most complex molecule first.
• Save hydrogen and oxygen for last (since they often appear in multiple compounds).
• Double-check by counting atoms again at the end.