(i) Take some broken pieces of egg shell in a test tube and add lemon juice to it. You could see bubbles of carbon-di-oxide evolving in the test tube. This is because of the chemical change between the two. Hence, we can say that evolution of bubbles serve as an indicator that of a chemical change.
(ii) When water is added to quicklime (calcium oxide) there will be evolution of lot of heat along with the formation of slaked lime (calciumhydroxide). This is a chemical change and it is indicated by the evolution of heat when the reaction sets in between quicklime and water.
(iii) Spoilage of food is a chemical change and it is indicated by the foul smell. So, change of odour is also an indicator of a chemical change.
(iv) When an iron nail is kept in water for a few days and taken out, the nail will become reddish brown in colour indicating that it has rusted. Rusting is a chemical change and it is indicated by a change in colour of the iron nail.
(v) A lump of curd is the precipitate that is obtained by the chemical reaction between hot milk and lemon juice. So, formation of precipitate is also an indication of a chemical change.
