Now moving on to the second type of decomposition reaction that is decomposition reaction due to light. For this we are going to take a China dish in which we have yellow coloured substance which is AgBr also called as silver bromide. And let us see what happens when you keep that silver bromide exposed to sunlight. There is formation of vapour along with change of colour from yellow to grey, formation of grey coloured substance. Now, what is that grey coloured substance? It is nothing but silver that is Ag and the vapours formed are of Bromine. Now in this reaction we took one reactant which in the presence of sunlight gave us two products, two simpler products that is Ag and Br. So, there was a splitting up reaction or the breaking down reaction, which is the decomposition reaction but it only and only took place because of sunlight, because it was being exposed to sunlight. So, it was decomposition due to light.

Now, next question would be, is the reaction balanced. Obviously not, because we can see on right hand side bromine is 2, left hand side it is 1. So, we need to balance on left hand side as well making it 2AgBr. But if we make 2AgBr, Ag becomes 2 so we need to balance on the right hand side as well making it 2Ag plus Br2. Now the reaction is balanced.

Now, let us consider one more similar kind of reaction. That is reaction of AgCl when it is exposed to sunlight. And when AgCl, a white coloured substance is exposed to sunlight similar kinds of observations were made, formation of grey coloured substance along with release of vapour. And the grey colour substance was again silver and the vapours are of chlorine. Again the same kind of question, is the reaction balanced? Obviously not, because on right hand side we have 2 chlorine and left hand side 1 chlorine. We need to balance it to make it 2AgCl. That makes Ag2. So, on right hand side also we need to make Ag2 that is 2Ag plus Cl2. Same thing happened, we took one reactant which in the presences of sunlight got split down into two simpler products Ag and Cl2, so, again a decomposition due to light.

Now, both these reactions are used in black and white photography during the process of developing and also a decomposition reaction that takes place due to light or in the presence of sunlight, is called as photolysis.

Moving on to the third type of chemical reaction, that is decomposition due to electricity. Now, water can be decomposed by electricity. So, the decomposition takes place because of third condition because of the electricity. For this we are going to take a simple experimental set up, wherein we have a plastic mug in which we have acidified water and we can also see two rods, graphite rod which are connected to the negative and positive terminal of the battery. Also there are two test tubes which are kept inverted over the graphite rod and there is a switch for manipulating the supply of electric current. And the moment the switch is put on electricity is going to start flowing. But what is this acidified water. An acidified water is the water mixed with few drops of acid. And what is the need for the acidified water? Answer is very simple, acidified water is used to produce ions that is for the process of ionisation because when there is ions then only electricity can flow. So, let us put the switch on and see the observation and look at the observation. And the moment the switch is put on we can see collection of gases towards the positive as well as the negative terminal. Towards the positive we have oxygen and towards the negative we have hydrogen. Now, what happened during the process is, there was water and the moment we supply electric current that water that is H2O got spilt up into its respective atoms hydrogen and oxygen. So, there was a splitting up process, because from one reactant that is H2O we got two simpler products H2 and O2. So there was splitting which took place only and only in the presence of electric current or because of supply of electricity. So there was a decomposition reaction taking place but it took place only because of supply of electric current or electricity. Reaction needs to be balanced so, 2H2O should give you 2H2 plus O2. Such kind of decomposition reaction which takes place due to electricity is called as electrolysis, also called as electrolytic decomposition.  Now, what are the uses for this electrolysis process? Uses includes, extraction of metals like sodium or aluminium and also for the process of electroplating.