Decomposition Reaction of Silver Chloride Explained

The question asks about the specific condition under which the chemical reaction \(2AgCl (s) \to 2Ag (s) + Cl_2 (g)\) occurs. This reaction represents the decomposition of solid silver chloride (AgCl) into solid silver (Ag) and chlorine gas (\(Cl_2\)).

Understanding the Photochemical Nature of AgCl

Silver chloride (AgCl) is known for its sensitivity to light. When exposed to light, particularly ultraviolet (UV) light present in sunlight, AgCl undergoes a decomposition process. This type of reaction, which is triggered by light energy, is called a photochemical reaction.

The energy from light photons is absorbed by the AgCl molecules, providing the necessary energy to break the bonds and form silver atoms and chlorine molecules.

The reaction equation illustrates this:

\(2AgCl (s) \xrightarrow{\text{Sunlight}} 2Ag (s) + Cl_2 (g)\)

Analyzing the Options

• 1. in dark: In the absence of light, this photochemical decomposition does not happen. Therefore, this option is incorrect.
• 2. in sunlight: Sunlight contains sufficient light energy (photons) to initiate and sustain the decomposition of AgCl. This is the primary condition for this reaction to occur readily.
• 3. on heating: While heating AgCl to very high temperatures (above 440 °C) can cause decomposition, it's not the typical or most common condition associated with this reaction, especially compared to light sensitivity. Light-induced decomposition happens at much lower temperatures.
• 4. under high pressure: Pressure changes primarily affect reactions involving a change in the number of moles of gas. While the reaction produces \(Cl_2\) gas, pressure is not the main factor driving the decomposition of solid AgCl. Light energy is the key factor.

Conclusion

Based on the light-sensitive nature of silver chloride, the reaction \(2AgCl (s) \to 2Ag (s) + Cl_2 (g)\) predominantly takes place in sunlight due to photochemical effects.