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Study Notes: Changes Around us - Science Olympiad Class 6

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. 

Can all Changes always be Reversed?

Any difference in the size or shape of an object is referred to as a change.

Changes are either reversible or irreversible.

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 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.

  • The 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: CookingFig: CookingFor example, when vinegar is mixed with the 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 the heating of limestone.
  • 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.

Question for Study Notes: Changes Around us
Try yourself:Which of the following is an example of a reversible change?
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Could there be Other Ways to Change?

Expansion and Contraction

When the temperature increases, the particle of a substance expands or becomes loose. When this happens, the material is said to undergo expansion.

When the temperature decreases, the particles of the substance contract or become tight. When this happens, the material is said to undergo contraction.

The amount of expansion or contraction varies in solids, liquids and gases.

There are physical changes that take place when a substance or material moves from one state of matter to another.

Water is a classic example as it can exist as either solid, liquid or gas.

Water at very low temperatures exists as a solid known as ice. On applying heat or increasing the temperature, the ice ‘melts’ to form water. The physical change when a solid changes to a liquid is called melting.

If we keep increasing the temperature, the water now starts to boil until it fully becomes water vapour. The physical change when a liquid changes to gas is called evaporation.

To get back the water from water vapour, it is possible by condensation – a physical change where the gas changes to a liquid. This is possible by lowering the temperature.

Changes in States of MatterChanges in States of Matter

Question for Study Notes: Changes Around us
Try yourself:
What is the physical change called when a solid changes to a liquid?
View Solution

Anomalous Expansion of Water

Water on cooling contracts up to 4∘C. On further cooling, up to 0∘C, water expands rather than contracting with a decrease in temperature. This means that as the temperature decreases from 4∘C to 0∘C, water expands. This behaviour is called the anomalous expansion of water.


Burning is an irreversible change where a substance burns to produce new material. These new materials are ash and some gases.

For example. paper is burnt to produce ash, which is different from paper in terms of appearance and properties.


The separation of the components of a mixture or an impure substance is carried out for the following purposes:

  • To remove the unuseful or harmful component.
  • To obtain the useful component.
  • To remove impurities for getting a pure sample.
The document Study Notes: Changes Around us | Science Olympiad Class 6 is a part of the Class 6 Course Science Olympiad Class 6.
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FAQs on Study Notes: Changes Around us - Science Olympiad Class 6

1. Can all changes always be reversed?
Ans. No, not all changes can be reversed. Some changes are irreversible and cannot be undone. For example, once a tree is cut down, it cannot be turned back into a living tree. Similarly, once a glass is broken, it cannot be restored to its original form.
2. What are some other ways to change?
Ans. There are many other ways to change. Some changes occur naturally, such as the changing seasons or the growth of plants. Other changes are caused by human intervention, such as technological advancements or social progress. Some changes are intentional, while others happen by chance.
3. How do changes around us affect our daily lives?
Ans. Changes around us affect our daily lives in many ways. For example, changes in the weather can impact our clothing choices and our activities for the day. Changes in technology can affect how we communicate and do our work. Changes in society can impact our beliefs and values.
4. Can changes be both positive and negative?
Ans. Yes, changes can be both positive and negative. For example, the invention of the internet has had many positive impacts, such as making information more accessible. However, it has also had negative impacts, such as contributing to the spread of misinformation.
5. How can we adapt to changes around us?
Ans. We can adapt to changes around us by being open-minded and flexible. It is important to stay informed about changes and to seek out new information and perspectives. We can also try to find ways to make the most of changes and to use them to our advantage.
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