The primary law of photochemistry is called the Grotthuss–Draper Law.
Grotthuss–Draper Law (Primary Law)
- Statement: Only the light that is absorbed by a substance can cause a chemical change.
- Meaning: If light hits a molecule but is not absorbed, it won’t make the molecule react.
Simple Explanation
- Imagine sunlight shining on a leaf: only the photons that are absorbed by chlorophyll help make food. The rest of the light just passes through or is reflected.
- So, absorption of light is essential for photochemical reactions.
Key Point
- This law is the foundation of photochemistry because it tells us that light must be absorbed to start any light-driven chemical reaction.