Reversible and Irreversible changes

Reversible and Irreversible changes:
Reversible Change:
        A Change which can be reversed is called a reversible change. In this change, the products formed can be converted back into their original forms. For example, Water can be changed into ice by placing it in the freezing chamber of the fridge. The ice so formed can be converted back into water by placing the ice outside the fridge.
        Some more examples of reversible changes are
            Boiling of water
            Melting of wax
            Stretching of a rubber band
Stretching of a spring
            Inflation of a ballon
            Ironing of clothes
            Folding of paper
Irreversible change:
        A change which cannot be reversed is called an irreversible change. In this change, the products cannot be converted back into their original form.
For example, When a paper is burnt, it changes to ash and smoke. From ash and smoke, we cannot get back paper. Thus, the change is irreversible.
Some more examples of reversible changes are
            Burning of fuels (like Wood, Coal and LPG)
            Cooking of food
            Grinding of wheat grains into flour
            Growth of a plant
            Formation of flower from bud
            Falling of leaves from a tree
            Ripening of fruits 
            Ageing of man and animals
            Death and decay of plants and animals
            Souring of milk
            Boiling of an egg (Raw egg to boiled egg)
Activity 

Take some dough and make a ball. Try to roll out a roti May be you are not happy with its shape and wish to change it back into a ball of dough again.
    
A ball of dough and a rolled out roti
Now, think about the three changes you observed .. What do they have in common? Was it possible to get the balloon back to its original shape and size? Was the size of the paper same as before and after making an aeroplane? Was it possible to get back the ball of dough again? What do you conclude? In each of the three activities, is it possible to get back to the material with which we started our activity? If the answer is yes, it means that the changes occurring in these activities can be reversed. 

Now, let us repeat the same activities with a difference.
ACTIVITY