Balance Fe+Cl_2→FeCl_3

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 a balanced element because there is the same number of atoms of ${\displaystyle Fe}$ in each side of the equation.

${\displaystyle Cl}$ is not a balanced element. To balance ${\displaystyle Cl}$, multiply ${\displaystyle C{l}_2}$ from the left side by ${\displaystyle 3}$ and ${\displaystyle FeC{l}_3}$ from the right side by ${\displaystyle 2}$.

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

${\displaystyle Cl}$ is a balanced element because there is the same number of atoms of ${\displaystyle Cl}$ in each side of the equation.