Why silver chloride turns grey in Sunlight?

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UPSC Geoscientist – 2021

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When silver chloride (AgCl) is exposed to sunlight, it undergoes a photochemical decomposition reaction. The light energy causes the decomposition of AgCl into silver metal (Ag) and chlorine gas (Cl₂). The silver metal produced is grey, which causes the white AgCl to turn grey. This reaction requires energy from sunlight, making it an endothermic process.
The reaction is: 2AgCl(s) + Sunlight → 2Ag(s) + Cl₂(g)

Sunlight decomposes silver chloride (AgCl) into grey silver metal (Ag) and chlorine gas. This decomposition is an endothermic reaction.

This photochemical reaction is the basis for early photography techniques (e.g., using silver halide photographic plates or paper). Silver bromide (AgBr) and silver iodide (AgI) also undergo similar photochemical decomposition when exposed to light.

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