# How do you write an equation to represent "Calcium sulfite decomposes to form calcium oxide and sulfur dioxide"?

Dec 21, 2015

${\text{CaSO"_text(3(s]) -> "CaO"_text((s]) + "SO}}_{\textrm{2 \left(g\right]}} \uparrow$

#### Explanation:

The first clue to go by is the fact that you're dealing with a decomposition reaction, so you know that calcium sulfite is the only reactant and that you have two products, calcium oxide and sulfur dioxide.

Start by focusing on the reactant, calcium sulfite.

As you know, the -ite suffix is used to distinguish between polyatomic anions that contain oxygen. These polyatomic anions go by the name of oxyanions.

More specifically, the -ite suffix is used for elements that can form multiple oxyanions to represent an oxyanion that contains fewer atoms of oxygen.

By comparison, for the same element, the -ate suffix is used to represent the oxyanion that contains more atoms of oxygen.

In this case, sulfite is the name given to the ${\text{SO}}_{3}^{2 -}$ anion. Sulfate, for example, is the name given to the ${\text{SO}}_{4}^{2 -}$ anion, since it contains an extra oxygen atom than the sulfite anion.

So, you know that the reactant is composed of calcium cations, ${\text{Ca}}^{2 =}$, and sulfite anions, ${\text{SO}}_{3}^{2 -}$. This means that you have

color(blue)("CaSO"_text(3(s]) -> ? + ?)

Next, focus on the oxide. Since calcium cations have a $2 +$ charge, and oxygen anions have a $2 -$ charge, &calcium oxide will simply be

$\text{Ca"^(2+)"O"^(2-) implies "Ca"_2"O"_2 implies "CaO}$

You now have

color(blue)("CaSO"_text(3(s]) -> "CaO"_text((s]) + ?)

Finally, focus on sulfur dioxide. Sulfur dioxide is a covalent compound, which means that you can conclude from its name that it contains

• one sulfur atom $\to$ sulfur has no prefix in the name of the compound
• two oxygen atoms $\to$ oxygen has a di- prefix in the name of the compound

Therefore, you can say that sulfur dioxide is ${\text{SO}}_{2}$. This gives you

$\textcolor{b l u e}{{\text{CaSO"_text(3(s]) -> "CaO"_text((s]) + "SO}}_{\textrm{2 \left(g\right]}} \uparrow}$