Define a photochemical reaction. Give one example.

A photochemical reaction is a chemical reaction that is initiated or facilitated by the absorption of light energy. When a molecule absorbs light, it can undergo various changes such as bond breaking, bond formation, or electronic transitions, leading to the formation of new chemical species. Photochemical reactions are prevalent in nature and play crucial roles in processes like photosynthesis, vision, and atmospheric chemistry.

One example of a photochemical reaction is the process of photosynthesis in plants. During photosynthesis, chlorophyll molecules absorb light energy, typically from sunlight, which initiates a series of photochemical reactions. These reactions convert carbon dioxide and water into glucose (a form of sugar) and oxygen gas, producing energy in the form of adenosine triphosphate (ATP) in the process. This reaction is vital for the sustenance of life on Earth as it serves as the primary mechanism by which plants produce food and release oxygen into the atmosphere.