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What does the Grotthuss-Draper law say about light absorption and chemical change?
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photochemical reaction
Chain of fluorescent tunicates.
The Grotthuss-Draper law is a fundamental principle in physical chemistry stating that radiation can only induce a photochemical reaction if the energy from that radiation is absorbed by the substance being affected.1
This law establishes that light must be absorbed by a molecule to trigger a chemical change, serving as a foundational concept for understanding how light initiates chemical reactions. It is distinct from, though related to, the photochemical equivalence law, which further quantifies this relationship by stating that for every quantum of radiation absorbed, one molecule of the substance reacts.123