Balance C_3H_7OH+O_2→CO_2+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.

${\displaystyle C}$ is not a balanced element. To balance ${\displaystyle C}$, multiply ${\displaystyle C{O}_2}$ from the right side by ${\displaystyle 3}$.

${\displaystyle H}$ is not a balanced element. To balance ${\displaystyle H}$, multiply ${\displaystyle H_{2}O}$ from the right side by ${\displaystyle 4}$.

${\displaystyle O}$ is not a balanced element. To balance ${\displaystyle O}$, multiply ${\displaystyle C_3{H}_{7}OH}$ from the left side by ${\displaystyle 2}$ and ${\displaystyle 3C{O}_2,4H_{2}O}$ from the right side by ${\displaystyle 8}$.

${\displaystyle O}$ is not a balanced element. To balance ${\displaystyle O}$, multiply ${\displaystyle O_2}$ from the left side by ${\displaystyle 5}$.

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

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

${\displaystyle O}$ is not a balanced element. To balance ${\displaystyle O}$, multiply ${\displaystyle 2C_3{H}_{7}OH}$ from the left side by ${\displaystyle 2}$ and ${\displaystyle 6C{O}_2,8H_{2}O}$ from the right side by ${\displaystyle 8}$.