Balance Fe_2O_3+H_2→Fe+H_2O

The law of conservation of mass states that matter cannot be created nor destroyed. There are no more or less atoms at the end of a chemical reaction than there were at the beginning. To balance a chemical equation, every element must have the same number of atoms on each side of the equation.

${\displaystyle Fe}$ is not a balanced element. To balance ${\displaystyle Fe}$, multiply ${\displaystyle Fe}$ from the right side by ${\displaystyle 2}$.

${\displaystyle O}$ is not a balanced element. To balance ${\displaystyle O}$, multiply ${\displaystyle H_{2}O}$ from the right side by ${\displaystyle 3}$.