Question

2g of silver chloride is taken in a china dish and the china dish is placed in sunlight for some time. What will be your observation in this case? Write the chemical reaction involved in the form of a balanced chemical equation. Identify the type of chemical reaction.

Answer 1

Silver chloride contains a chlorine anion and a silver cation. When exposed to sunlight, the cation turns into its respective metal eventually. The crystalline solid breaks down and is followed by a colour change. The colour of the compound becomes darker as a result of the reaction.

Complete answer:

Chemical formula of silver chloride is AgCl. Silver chloride is a light sensitive compound i.e. it reacts in presence of light.
Silver chloride consists of closely packed silver cations, $A{{g}^{+}}$ and chlorine anions, $C{{l}^{-}}$ the positive charge on silver depicts that it has an electron missing and the negative charge on chlorine depicts it has one electron in excess.

When silver chloride is exposed to sunlight, being light sensitive it undergoes a chemical reaction. We can write the chemical reaction as:
$2AgCl+light\to 2A{{g}^{+}}+C{{l}_{2}}(g)+2{{e}^{-}}$

Chlorine undergoes oxidation by releasing the 2 electrons. These two electrons are taken up by silver ion to be reduced to silver metal:
$2A{{g}^{+}}+2{{e}^{-}}\to 2Ag(s)$

Therefore, we can write the balanced chemical equation for the reaction as:
$2AgCl(s)+light\to 2Ag(s)+C{{l}_{2}}(g)$

Silver chloride is a white crystalline solid but due to this reaction as it breaks down into silver metal and chlorine gas, the colour turns to grey due to silver metal. So our observation is the compound turns from white to grey in presence of sunlight. This type of chemical reaction is called photochemical decomposition reaction.

Photochemical because it is a chemical reaction occurring in presence of sunlight and decomposition as AgCl breaks or decomposes into chlorine and silver.

Note:
The same products are obtained if silver chloride is heated instead of placing it in sunlight but still it is considered a photochemical reaction as it behaves the same in presence of light. It is also important to remember that heat is not the only factor which causes decomposition. Decomposition can be caused by light and electricity as well.