Explain the properties of alkanes and write the balanced symbol equation for the complete combustion of methane.

There is 1 carbon atom on the left ($\text{CH}_4$), so there must be 1 carbon atom on the right.

There are 4 hydrogen atoms on the left ($\text{CH}_4$). On the right, $2\text{H}_2\text{O}$ means $2 \times 2 = 4$ hydrogen atoms. Hydrogen is already balanced.

On the right side, there are 2 oxygen atoms from $\text{CO}_2$ and $2 \times 1 = 2$ oxygen atoms from $2\text{H}_2\text{O}$, totaling $2 + 2 = 4$ oxygen atoms. Therefore, there must be 4 oxygen atoms on the left. Since oxygen is in the form of $\text{O}_2$, we need $4/2 = 2$ molecules of $\text{O}_2$.

The completed equation is: