Look at the following chemical equation. Hg + O2 = HgO2 How many atoms are on each side of the equation?

To solve this problem, look at each side of the equation individually.

1. First look at the reactant side: Hg + O2

There is one Hg (Mercury) and two O (Oxygen)

1+2 = 3

There are 3 atoms on the reactant side

2. Then look at the product side: HgO2

There is one Hg and 2 oxygens yet again

1+2=3

There are three atoms on each side of the equation. You can simply count the atoms or remember the Law of Conservation of Mass.