Balance H2 + O2 -> H2O using the smallest whole-number coefficients. Explain why the formulas must stay the same.
2 H₂ + O₂ → 2 H₂O
- Count atoms before balancing
The original equation has two hydrogen atoms and two oxygen atoms on the left, but two hydrogen atoms and one oxygen atom on the right.
- Balance oxygen with a coefficient
Put 2 in front of H₂O. This makes two oxygen atoms on the right, but now there are four hydrogen atoms on the right.
\(\mathrm{H}_2+\mathrm{O}_2\rightarrow2\mathrm{H}_2\mathrm{O}\)
- Balance hydrogen
Put 2 in front of H₂. The numbers of atoms now match. The coefficients 2:1:2 have no common divisor greater than one.
\(2\mathrm{H}_2+\mathrm{O}_2\rightarrow2\mathrm{H}_2\mathrm{O}\)
- Keep the substances unchanged
A coefficient changes the number of molecules. A subscript is part of the chemical formula. Replacing H₂O with H₂O₂ would change water into a different substance, not balance the original equation.
Hydrogen: 4 atoms on each side. Oxygen: 2 atoms on each side. Every species is neutral, so total charge is zero on both sides.