Question

Potassium chlorate, `KClO_3`, decomposes to form potassium chloride, `KCl` and oxygen gas. How do you write a balanced equation for this decomposition reaction?

Answer 1

`"2KClO"_3("s")" + heat"` `rarr` `"2KCl(s)" + "3O"_2("g")"`

Explanation:

`"KClO"_3("s")" + heat"` `rarr` `"KCl(s)" + "O"_2("g")"`

Notice that the number of atoms of `"K"` and `"Cl"` are the same on both sides, but the numbers of `"O"` atoms are not. There are 3 `"O"` atoms on the the left side and 2 on the right. 3 and 2 are factors of 6, so add coefficients so that there are 6 `"O"` atoms on both sides.

`"2KClO"_3("s")" + heat"` `rarr` `"KCl(s)" + "3O"_2("g")"`

Now the `"K" and "Cl"` atoms are not balanced. There are 2 of each on the left and 1 of each on the right. Add a coefficient of 2 in front of `"KCl"`.

`"2KClO"_3("s")" + heat"` `rarr` `"2KCl(s)" + "3O"_2("g")"`

The equation is now balanced with 2 `"K"` atoms, 2 `"Cl"` atoms, and 6 `"O"` atoms on both sides.