Why do decomposition reactions typically have compounds as reactants, whereas combination and displacement reactions have one or more elements?

Elements cannot be decomposed to form new element, that’s why all decomposition reactions typically have compounds as reactants. In combination and displacement reactions, there are elements as reactants because in these reactions, decomposition is not required.

In decomposition reaction, one compound is decomposed and forms one or more products. As element cannot be decomposed, hence this type of reactions has compounds as reactants.

In combination reaction, two or more reactants combine to form a single product.

In displacement reaction, no of substances on the both side of the equation remain the same but the atoms exchange places to form the product.

Elements can be used to form product in these types of reactions.

Elements cannot be decomposed to form new element, that’s why all decomposition reactions typically have compounds as reactants. In combination and displacement reactions, there are elements as reactants because in these reactions, decomposition is not required.