Here's the breakdown:
* Sunlight's Energy: Sunlight contains ultraviolet (UV) radiation, which carries enough energy to break the chemical bond between silver and chlorine in silver chloride.
* Decomposition: When AgCl absorbs UV light, the energy causes the chloride ions (Cl-) to be released as chlorine gas (Cl2), leaving behind silver metal (Ag).
* Color Change: Silver metal is grey in color, resulting in the observed grey discoloration of the silver chloride.
The reaction can be represented by the following equation:
2AgCl(s) → 2Ag(s) + Cl2(g)
Factors affecting the rate of discoloration:
* Intensity of sunlight: Stronger UV radiation leads to faster decomposition.
* Presence of impurities: Some impurities can act as catalysts, accelerating the process.
* Temperature: Higher temperatures generally speed up chemical reactions.
Note: This is why silver chloride is used in photography. The light-sensitive crystals are exposed to light, causing the decomposition of silver chloride. The amount of light that hits each part of the film determines the amount of silver metal formed, resulting in a photographic image.
