Question

Give an example of a reaction that requires light.

Answer 1

We know that photo decomposition Reaction is a chemical reaction in which a compound gets broken down into simple substances under its exposure to light. This reaction is also known as Photolysis or Photodissociation reaction.

Complete answer: As we know that the one type of chemical reaction is decomposition reaction, in which the reactants are broken down into small products, and photochemical reaction is one of the subdivisions of decomposition in which light is used for decomposition. Decomposition is one of the types of chemical reactions in which the reactant which is complex breaks down into simpler substances under the action of heat. In our daily life we can see this reaction everywhere, right from ourselves, home or labs. The common day today examples include digestion of food to give out carbon dioxide and water and energy, heating experiments in the lab, like breaking off Calcium Carbonate into Calcium oxide and Carbon dioxide gas, etc.
This heat can be supplied in multiple ways. The different ways in which heat can be supplied, gives different names to decomposition reactions. Photochemical decomposition: When Photon or light energy is used for decomposition or breaking of complex substances into simpler substances, then this reaction is called a photochemical decomposition reaction. The examples with reactions can be given as under, Photochemical Decomposition of silver chloride and silver bromide to give silver and chlorine or bromine gas respectively. The reaction is given by; $2AgCl\to 2Ag+C{{l}_{2}}.$
Therefore, the photolytic decomposition reactions take place in the presence of light.

Note:
Remember that the energy is absorbed in bond breaking, so always decomposition reactions are endothermic reactions. These rays which are absorbed in photochemical decomposition, are ultraviolet radiations, or visible radiations or Infrared radiations.