NCERT Solutions For Class 6 Science Chapter 6 Changes Around Us are given in a detailed and easy way. In NCERT class 6 science book introduces various important topics like reversible and irreversible changes, chemical changes, physical changes, etc. Here, students can also download NCERT Solutions for class 6 science PDF.
The NCERT Solutions for chapter 6 Changes Around Us is explained in a simple language and students can easily understand the answers of the respective questions. These solutions can help the students to clear all their doubts and have proper understanding of the related topics.
This chapter specifically deals with changes – reversible and irreversible. It highlights all the chemical and physical processes that affect our world. It provides a superficial insight into the basics of chemistry. Certain reactions take place where the elements change or merge into something new. The involved elements cannot be reconstituted back into their origins and these are called irreversible reactions.
When you burn a paper, you cannot convert the ashes back in paper – this is an example for irreversible reaction. When you burn a candle though, the wax melts and it can be reconstituted into another candle. This is a reversible reaction. Let’s explore more of these changes below.
- We usually shorten the length of the pant by folding it, when walking through a waterlogged area. Is the change reversible or not?
The change is reversible and it can be done by unfolding the pants.
- You accidentally drop your Barbie doll and break it. Is this reversible or not?
No, The change (breaking of Barbie doll) cannot be reversed.
- Among the examples listed down, state whether they are reversible or not.
|S.no||Changes||Reversible or irreversible|
|1||Dissolving salt in water|
|2||Melting of ice cubes|
|3||Release of steam from the cooker|
|4||Ripening of a fruit|
|5||Freezing orange juice by cooling|
|6||Melting of wax|
|S.no||Changes||Reversible or irreversible|
|1||Dissolving salt in water||Reversible|
|2||Melting of ice cubes||Reversible|
|3||Release of steam from the cooker||Irreversible|
|4||Ripening of a fruit||Irreversible|
|5||Freezing orange juice by cooling||Reversible|
|6||Melting of wax||Reversible|
- Is the change where you draw a picture on a drawing sheet, reversible?
If we draw a picture using a pencil sketch, then the change is reversible.
But, if the picture is drawn using an oil color, sketch, watercolors or pen, then the change is irreversible.
- State the examples for reversible and irreversible changes.
i) If we draw a picture using a pencil sketch, then the change is reversible. However, if the picture is drawn using an oil color, sketch, watercolors or pen, then the change is irreversible.
ii) If we inflate a tire, the shape and size of the tire changes. This change can be reversed, but if the tire bursts while inflating, then the change is irreversible.
iii) Melting of ice is a reversible change whereas cooking of food is an irreversible change.
- For a fractured bone, Plaster of Paris bandage is preferred. Why? State whether the change is reversible or irreversible.
Plaster of Paris bandage is preferred because it becomes hard on drying to keep the bone immobilized which help in recovering at a faster rate. Since there is a change of state, a new product is formed which cannot be brought back to its original form. So the change is irreversible.
- If you leave a piece of iron outside for a long time it turns brown leading to the formation of rust. Is the change reversible or irreversible?
The formation of rust is completely a new substance due to the reaction of oxygen with the iron, which is termed to be a chemical change. Therefore, it not possible to avoid the rust formation and the change is irreversible.
- State a few examples for slow changes.
i) Germination of seed
ii) Rusting of iron
iii) Curdling of milk
- State a few examples for fast changes.
i) Burning of candle
ii) Burning of paper
iii) Inflating tire
- State any two examples of reversible changes.
i) Melting of ice
ii) Melting of candle wax
- State any two examples of irreversible changes.
i) The ingredients like flour, egg and sugar is converted to cake
ii) Cooking of food
iii) Burning of fuel
12.Deforestation is an irreversible change. Why?
Once the trees are cut, the same tree cannot be planted. So deforestation is considered as an irreversible change.
13.The explosion of a cracker is a chemical change. Explain.
The explosive reactants of a cracker are transformed into gaseous products along with heat and light. Thus, it cannot be brought back to the original form. Hence, it is a chemical change.
- Blacksmith heats the metal rim to fix it on the cartwheel. Explain.
The metal rim will be smaller than its usual size. On heating, the metal rim expands and fits onto the wheel. Similarly, on cooling, the metal rim contracts and fits tightly to the wheel.
- Define slow changes and fast changes. State a few examples.
The changes, which take place slowly over a period is called slow changes.
Ex-Germination of seed, formation of day and night and Rusting of iron
The changes which take place quickly is called fast changes.
Ex: Burning of paper, Melting of a candle and blowing of balloons.
- Classify the following as slow or fast changes:
i) Growth of a plant
ii) Formation of clouds
iii) Formation of sugar solution
iv) Inflation of tire
v) Melting of chocolate
i) Slow change
ii) Slow change
iii) Fast change
iv) Fast change
v) Fast change
- What are the changes taking place in our body?
a) The height of the person increases
b) Nails grow
c) The weight of the person increase
d) Our hair grows.
- Formation of clouds is usually a physical change. Justify the statement.
The formation of clouds is a physical change because there is a phase transformation cycle of natural water from liquid to gas and then, gas to liquid. Hence, the property of water never changes.
- Explain the physical changes and chemical changes with an example.
i) The changes where the physical property of the substance varies without any formation of new products.
ii) These changes are reversible and the products are identical to the reactants.
Ex: Melting of ice, during this change the water changes from its solid form to liquid form, melting of wax.
i) The changes where the chemical property of the substance varies with the formation of new products.
ii) These changes are irreversible and the products are not identical to the reactants.
Ex: Formation of curd from milk, rusting of iron.
20.What will be the change when sugar is heated?
When sugar is continuously heated, a black powdery substance is formed which is called charcoal. Since a new product is formed, it is termed to be a chemical change.
21.Give some examples of changes, which take place on their own.
The changes that take place on their own are
i) Shedding of leaves
ii) Ripening of fruits
iii) Growth of the body
iv) Blooming of flowers
- How do we convert milk into curd and what type of change is it?
The milk is taken in a vessel and a small quantity of curd is added into it. The milk is stirred and it is kept aside for few hours without any disturbance. Finally, the milk is converted into curd. However, curd formed cannot be converted into milk again indicating that it is an irreversible change.
NCERT Solutions For Class 6 Science Chapter 6 specifically deals with the changes that happens around us. This involves physical and chemical reactions and these may or may not be reversible. For instance, when we burn things like paper and cardboard, the change is irreversible because the matter that is formed cannot be reconstituted back into its original elements.
Similarly, when a fruit ripens, it is a irreversible change. Chemicals in the fruit cause it to start ripening – human intervention can slow down or speed up this process, but it cannot be reversed. That's why you throw out an apple if it becomes too ripe and starts decaying. Processes such as turning water to steam is reversible because steam is still water and does not break into its components – hydrogen and oxygen.
Then there are changes that affect the object, such as heating a metal. This action causes the metal to expand. This principle is used by blacksmiths to fix a metal rim around the wheel. On heating, the metal rim expands and slips over the wheel easily. But once it starts cooling, the rim contracts and fits tightly around the wheel.
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