When a chemical change occurs, the event is usually accompanied by which of the following?

• A. A color change only
• B. The formation of a solid
• C. The release of energy
• D. The emission of light

Answer: (C)

When a chemical change happens, bonds are broken and new bonds form, which changes the energy of the system. A common consequence of this bond rearrangement is the release of energy, often seen as heat and sometimes as light. This makes energy release a typical indicator that a chemical change is occurring.

Color changes, solid formation, or light emission can occur in some reactions, but they don’t happen in every case. A color change only happens if the substances involved alter how they absorb or reflect light; a solid form (precipitation) occurs in specific reactions where a new solid compound forms from solutions; light emission happens only in certain reactions that release photons. Therefore, the most general and often observed accompaniment to a chemical change is the release of energy.