In a decomposition reaction, what happens to the reactants?

In a decomposition reaction, the characteristic process involves the breakdown of a compound into simpler substances or elements. This is typically initiated by the addition of energy, such as heat, light, or electricity, which facilitates the separation of the bonded atoms or molecules in the reactant.

For example, when calcium carbonate decomposes upon heating, it breaks down into calcium oxide and carbon dioxide. This highlights the fundamental nature of decomposition reactions, where one reactant transforms into multiple products that are simpler in structure.

The other answer choices do not accurately reflect what occurs in a decomposition reaction. The notion of combining to form a single product is more representative of synthesis reactions. Saying the reactants remain unchanged contradicts the very definition of any type of chemical transformation. The concept that decomposition only produces gases is also inaccurate, as decomposition can yield solids, liquids, or gases depending on the substances involved. Thus, option C effectively captures the essence of what happens to reactants in a decomposition reaction.