Question

What is photochemical decomposition?

Answer 1

Hint: First of all, to approach this question, we need the basic knowledge of what chemical reactions are and the different types of chemical reactions.
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.

Complete step by step answer:

Let us begin by understanding the term chemical reaction, and then types of chemical reaction.
Chemical reactions is the process in which reactants are converted to new products.
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.
Thermal decomposition: When supplying heat externally by gas flame or burner flame, the complex substance breaks into simpler substances.
Examples can be taken of calcium carbonate breaking into calcium oxide and carbon dioxide.
$CaC{O_3}\xrightarrow{\Delta }CaO + C{O_2} \uparrow $
Electrolytic decomposition: When electric current is passed through an aqueous solution of a compound, then decomposition of substance takes place.
Examples can be taken as electrolytic decomposition of water into Oxygen and Hydrogen gas.
\[2{H_2}O\xrightarrow{{Electricity}}2{H_2} + {O_2}\]
Now, after understanding in detail about the definition of chemical reaction, decomposition reactions and 2 types of decomposition. We are coming to our point of photochemical decomposition reaction.
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.
\[
  2AgCl\xrightarrow{{h\nu }}2Ag + C{l_2} \\
  2AgBr\xrightarrow{{h\nu }}2Ag + B{r_2} \\
 \]
Here, above the arrow \[h\nu \] is written which indicates the presence of Energy of photon, or light.

Note:
Here, in a decomposition chemical reaction, whatever energy is given in the form of heat, electricity or light energy will help in bond breaking of complex substances to give out simpler substances.
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.