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 a yellow colored substance which is AgBr also Silver Bromide. And let us see what happens when you keep that silver bromide exposed to sunlight? There is formation of vapor along with change of color from yellow to gray, formation of gray colored substance.
Now what is that gray colored substance, it is nothing but silver, that is Ag and the vapors formed are of Bromine? So 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 a decomposition reaction but it need 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 the right hand side Bromine is two, left hand side it is one. So we need to balance on left hand side as well, make it 2AgBr. But if we make 2AgBr, Ag becomes two, so you need to balance on the right hand side as well making 2Ag + 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 colored substance is exposed to sunlight, similar kind of observations were made, formation of gray colored substance along with release of vapor and that gray colored substance was again silver and the vapors are of Chlorine. Again the same kind of question is the reaction balanced? obviously not because on right hand side we have two chlorine and on the left hand side one chlorine, so you need to balance it, make it 2AgCl, that make Ag 2, so right hand side also we need to make Ag 2, i.e., 2Ag + Cl2. Same thing happened we took one reactant which in the presence 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 onto the third type of chemical reaction, that is decomposition due to electricity.
Now what all can be decomposed by electricity? So its decomposition takes place because of the third condition that is 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 rods which are connected to the negative and positive terminals of the battery, also there are two test tubes which are kept inverted over the graphite rod and there’s 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 a water mixed with dew 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 ionization 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 collection of gases towards and positive as well as the negative terminal. Towards the positive we have oxygen and towards the negative we have hydrogen. Now what happens during the process is there was water and the moment we supplied electric current that water, that is H2O got split down 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 +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 include extraction of metals like sodium or aluminum and also for the process of electroplating.