CHANGES AROUND US:
Every day, we see different types of changes around us, like day turning into night, the season changing from winter to summer, melting of ice to water, cooking of food, and so on. Changes take place around us all the time. However, all changes are the same. We get back the original substance in some, and can't get them back in others. A reversible change is a change that can be undone or reversed.
- Melting is an example of a reversible change.
- Boiling, evaporation and condensation are all examples of reversible changes.
- For example, if you could capture all the steam that is made when a kettle boils, you could turn it back into water by cooling it.
- Some other examples of reversible changes are the melting of ice, folding a paper and blowing a balloon.
- A blacksmith changes a piece of iron into different tools. For that, a piece of iron is heated to red hot. This also softens it. It is then beaten into the desired shape. It is a reversible change.
An irreversible change is a permanent change that cannot be undone. In an irreversible change, new substances are formed.
- Cake batter is made from eggs, flour, sugar and butter. Once the cake has been baked, you cannot get the ingredients back.
- Heating a substance can cause an irreversible change.
- Cooking is another example. We cannot get back the substances that we originally started with
- Mixing substances can also cause an irreversible change.
Fig: CookingFor example, when vinegar is mixed with bicarbonate of soda, you can observe the release of carbon dioxide gas in the form of bubbles. Again, here, we cannot get back the original substances.
- Some other examples of irreversible changes are the digestion of food and heating of lime stone.
- The burning of wood is also an irreversible change. Once wood is burned, it changes to ash, and we cannot get back the wood again.
Finally, our growth itself, as you can see, is an irreversible change.