Express the following chemical changes in the form of chemical equations and identify what types of chemical reactions they are.
A piece of (a) sulphur and (b) charcoal burns vigorously when dropped in molten potassium nitrate, because potassium nitrate decomposes to form potassium nitrite and oxygen and this oxygen helps to burn charcoal and sulphur giving out carbon dioxide and sulphur dioxide, respectively.

Explanation

`2KNO_3 to 2KNO_2 + O_2 to `(1)
`S + O_2 to SO_2 to ` (2)
`C + O_2 to CO_2 to` (3)
The first reaction represents the decomposition of potassium nitrate to form potassium nitrite and oxygen. Oxygen liberated helps burn sulphur and charcoal to give sulphuric dioxide and carbon dioxide as given in reactions (2) and (3). Reaction (1) is a decomposition reaction, whereas reactions (2) and (3) are combination reactions.