Chapter 6

Changes Around Us

 

Introduction

Things around us are constantly changing every moment - from the growth of our hair and nails, to the expansion and contraction of our lungs when breathing, to the moon's motion. As a result, our surroundings are continuously changing. Some of these modifications are short-lived, which means we may reverse them, and others are permanent, which means we cannot reverse them. A handful of these changes are hardly visible. Let us look at what such changes are and how these changes occur.

A change is defined as any variation in the form or size of an object. Some changes can often be undone, while others cannot. Changes may be classified into two major groups based on this: reversible and irreversible changes -

(1) Changes that may be undone or reversed are reversible.

Reversible change occurs when you can return to the original material. In the vast majority of situations, new material is not generated due to a reversible transformation. For example, drying clothes, boiling milk, stretching a rubber band, and setting ice. The physical qualities of a substance can alter at any time. When water heats up, for example, it turns into steam.

(2) Irreversible changes cannot be undone or reversed. It is the kind of change you can't undo with any physical or chemical method, regardless of what you do. During this process, new material is usually always created. An example of an irreversible change is the combustion of coal, which results in a chemical change. It is permanent because a new chemical is generated that we can never convert back to coal. Other examples include burning coal to form ash, making curd from milk, grinding grains to form flour, and blooming a flower.

Besides reversible and irreversible changes, there are two further changes to consider: physical and chemical changes.

(1) Physical changes impact a substance's physical qualities but not its chemical properties. For instance, boiling water, freezing water, melting wax, etc.

  • Physical changes do not typically involve the generation of energy.
  • During such physical changes, no new elements are generated.
  • Unlike chemical changes, physical changes allow the original material to be restored. Water, for example, may be transformed back into a liquid state from steam.
  • Physical change is just temporary and does not last.

(2) Chemical changes influence a substance's chemical and physical qualities. For example, food digestion, coal or paper combustion.

  • A chemical change is always accompanied by forming one or more new compounds. For example, coal combustion produces ash and gases such as carbon dioxide and sulphur dioxide.
  • Chemical changes frequently result in the production of energy in some form.
  • Most chemical changes are irreversible, so we cannot restore the original material.

When the temperature rises, the atoms in a material stretch or loosen. During summer, the railway tracks are a typical instance of expansion since steel extends when heated. When the temperature is lowered, the particles of a material compress and tighten. Railway tracks in the winter are typical of this contraction when steel contracts in cold temperatures. The expansion and contraction are different for different states of matter, such as solids, liquids, and gases.

Water is a wonderful example that has all of this since it can transition into liquid (water), solid (ice), and gas (steam). Water freezes at temperatures below or zero degrees celsius. This change from liquid to solid is referred to as freezing. When you increase the temperature or apply heat, it transforms into a liquid. This change from solid to liquid is known as melting, and the liquid will remain liquid until the temperature hits 99°C. When the temperature hits 100°C, water begins to boil and becomes steam. This process is known as evaporation.

Water may also be transformed from steam to liquid form through condensation. Condensation is how the physical state of matter changes from gaseous to liquid. This process is accomplished by reducing the temperature of the substance.

Burning, also known as combustion, is an irreversible process in which a material burns to create a new substance. Coal combustion is an excellent example of this; burning coal creates fly ash and numerous other gases such as carbon dioxide, sulphur dioxide, and fine particles, all of which cause pollution.

Many of the materials you see are not in their natural state. Instead, they are a combination of two or more chemicals. We can segregate different compounds in a mixture to acquire the various elements that form the mixture. Water sedimentation is an excellent example in which pollutants such as sand and pebbles are separated from the water to yield pure water.

1. To walk through a waterlogged area, you usually shorten the length of your dress by folding it. Can this change be reversed?

2. You accidentally dropped your favourite toy and broke it. This is a change you did not want. Can this change be reversed?

3. Some changes are listed in the following table. For each change, write the answer in the blank column, whether the change can be reversed or not.

Question Change Can it be reversed? Yes or No
1 The sawing of a piece of wood  
2 The melting of ice candy  
3 Dissolving sugar into water  
4 The cooking of food  
5 The ripening of a mango  
6 Souring of milk  

 

4. A drawing sheet changes when you draw a picture on it. Can you reverse this change?

5. Give examples to explain the difference between changes that can or cannot be reversed.

6. A thick coating of a paste of Plaster of Paris (POP) is applied over the bandage on a fractured bone. It becomes hard on drying to keep the fractured bone immobilised. Can the change in POP be reversed?

7. A bag of cement lying in the open gets wet due to rain during the night. The next day the sun shines brightly. Do you think the changes, which have occurred in the cement, could be reversed?

Now let us learn the Ncert solutions class 6 Science chapter 6.

Answers to NCERT solution exercises

Here are the Ncert solutions for class 6 Science Chapter 6 Changes Around Us

1. Yes, folding a cloth is a physical process and can be reversed. You can reverse the process by simply unfolding the dress after passing through the area filled with water.

2. No, we cannot reverse the breaking of a toy.

3.

Question Change Can it be reversed? Yes or No
1 The sawing of a piece of wood No
2 The melting of ice candy Yes
3 Dissolving sugar into water Yes
4 The cooking of food No
5 The ripening of a mango No
6 Souring of milk No

4. If we use a pencil to draw on a sheet of paper, we can reverse this process by erasing the drawing from the paper. If permanent pens or colours are used to draw on the paper, then we cannot reverse this change.

5. Most physical changes can be reversed while chemical changes cannot be reversed. Here are a few examples of reversible and non-reversible changes:

Changes that can be reversed Changes that cannot be reversed
Blowing a balloon without bursting it. Blowing a balloon and bursting it.
Rolling a dough ball. Making roti from a dough ball.
Folding a piece of paper to make an aeroplane. Cutting a shape from a sheet of paper.
Freezing water to form ice. Burning of an incense stick.
Opening and closing of touch-me-not plant. Curdling of milk.

 

6. No, the hardening of the Plaster of Paris is a non-reversible process. The powder form of Plaster of Paris reacts when mixed with water and forms a new compound. This is a chemical process that is non-reversible.

7. Cement and water undergo a chemical reaction when mixed together. If a bag of cement gets wet in the rain, we cannot reverse this change.

Q. How many types of changes occur around us?

Ans. Two types of changes occur around us. These are reversible and irreversible changes.

Q. How can we bring about a physical change in any substance?

Ans. A physical change means a change in the form or shape of an object or substance. For example, we can change the shape of an object by cutting or breaking it or by applying force. We can also change the form of a substance by applying heat or decreasing temperature.

Q. A potter uses clay to make pottery. Can we reverse this change?

Ans. A potter gives shape to clay and forms various objects through pottery. As long as the clay is wet, we can reverse the change and reform the object into clay again. But, if the pottery has been dried or heated, the change becomes permanent, and we cannot reverse this change.

Q. Knitting of a sweater using wool is reversible or irreversible?

Ans. Knitting a sweater using wool is a reversible change. We can easily open the knitting and get the original wool back from the sweater.

 

The changes around us, class 6 chapter, is an important part of a child's understanding of reversible and irreversible changes. It's amazing to realise that everything around us is always changing. Many changes are solely reliant on heat, and the degree and rate of change are determined by the amount of heat delivered. If you apply enough heat, you can modify the status of anything in your surroundings. For example, when basic materials like water are modified, the consequences vary from those of substantial compounds like coal.

Learn more about the changes around us, class 6 chapter with graphics and animation through interactive videos on the MSVgo website. MSVgo also offers a timely resolution of doubts and queries of students. You can learn about class 6 Science Chapter 6 Changes Around Us through the MSVgo website and app. You can also download the MSVgo app for android or iOS and get access to more than 15,000 videos and 10,000 questions. So, download the MSVgo app now!

 

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