Humber Admissions Practice Test

What defines a decomposition reaction?

1. Production of two or more new substances

2. Breakdown of a single compound into simpler substances

3. Combination of reactants to form a compound

4. Displacement of one element by another

The correct answer is: Breakdown of a single compound into simpler substances

A decomposition reaction is defined as the breakdown of a single compound into simpler substances. This type of reaction typically involves a single substance that, when energy is applied (through heat, light, or electricity), splits into two or more simpler products. For example, when water (H₂O) is subjected to electrolysis, it can decompose into hydrogen (H₂) and oxygen (O₂) gases. This characteristic of transforming one compound into different, simpler components is what distinctly marks a decomposition reaction compared to other types of chemical reactions. The other options refer to different reaction types: production of two or more new substances corresponds to a synthesis or combination reaction, where elements or simpler compounds combine to form a more complex one. The combination of reactants to form a compound describes synthesis reactions, while displacement reactions involve one element replacing another in a compound. Understanding these distinctions helps clarify the unique nature of decomposition reactions.