The Grotthuss–Draper Law is the primary law of photochemistry.
Statement:
Only the light that is absorbed by a substance can cause a chemical change.
Simple Explanation:
- If light hits a molecule but is not absorbed, no reaction will happen.
- Example: In photosynthesis, only the light absorbed by chlorophyll helps the plant make food. The rest of the light just passes through or is reflected.
Key Point:
- Absorption of light is essential for any photochemical reaction.
- This law is the foundation of photochemistry, because it tells us which photons actually drive reactions.