HESI A2 Chemistry Practice Test

A decomposition reaction is characterized by the process of breaking down a compound into its simpler constituents, which can include elements or smaller compounds. This type of reaction can be represented generally by the formula:

\[ AB \rightarrow A + B \]

where \( AB \) is the compound being decomposed into its parts \( A \) and \( B \). Decomposition reactions often require an input of energy, which can come in the form of heat, light, or electricity.

For example, when calcium carbonate (\( CaCO_3 \)) is heated, it decomposes into calcium oxide (\( CaO \)) and carbon dioxide (\( CO_2 \)).

This is distinct from other types of reactions listed. A combination reaction involves the merging of two or more substances to form a single product; a synthesis reaction refers to a similar process where elements combine to form a more complex compound. Combustion reactions involve the reaction of a substance with oxygen, typically resulting in the release of energy in the form of heat and light, producing new substances, mainly oxides.

Overall, a decomposition reaction is specifically about breaking down a compound, which is what makes it the correct answer to the question posed.