Irreversible Changes


•    Some changes cannot be reversed. These are called irreversible changes.

•    Irreversible changes are permanent. For example, an unripe mango is green and sour, but on ripening it usually becomes yellow and sweet.


Ripening of fruits:

•    Ripening of fruits is an irreversible change because it is not possible to get unripe fruits from ripened or mature fruits.


Growth of a baby:

•    Growth of a baby into an adult is irreversible because the man/woman cannot turn back into a baby.


Pencils and erasers:

•    Pencils and erasers get reduced in size with regular use. This is also an irreversible change.

•    There are a large number of irreversible changes that take place around us.

•    These result in a new material being produced, which may or may not be useful.


Cooking of food:



•    Cooking of food takes place on heating uncooked food. For example, making chapattis from flour, cooking rice, baking a cake, making an egg omelette or a fish fry are different forms of cooking.

•    We cannot get back the ingredients in their original form after cooking.

•    So, cooking of food is an irreversible change.

•    Buds change into flowers.

•    Blooming of flowers is an irreversible change because flowers cannot change back into buds.


Curdling or souring of milk:

•    What happens to the raw milk kept overnight and not refrigerated particularly in summers?

•    There are some changes that take place in the milk.

•    This is called curdling or souring of milk, which is an irreversible process.

•    Curdling of milk is also done by adding lemon juice to milk for making cottage cheese or paneer.




•    Heating can cause an irreversible change.

For example, we heat a raw egg to cook it.



•    Mixing substances can cause an irreversible change.

•    For example, when vinegar and sodium bicarbonate are mixed, the mixture changes and carbon dioxide is evolved.



•    If we burn a paper, it turns into ash.

•    It is a new substance that differs from the paper in its physical and chemical properties.

•    This ash cannot be turned back into paper.

•    Burning is therefore an irreversible change.