Basic Science Solutions for Class 6 Science Chapter 6 A Study Of Changes are provided here with simple step-by-step explanations. These solutions for A Study Of Changes are extremely popular among Class 6 students for Science A Study Of Changes Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Basic Science Book of Class 6 Science Chapter 6 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Basic Science Solutions. All Basic Science Solutions for class Class 6 Science are prepared by experts and are 100% accurate.

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A change that can be reversed by reversing the conditions is known as a reversible change.

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A change that cannot be reversed by reversing the conditions is known as an irreversible change.

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Physical changes are changes by which no new substance is formed. These changes can be reversed by reversing the conditions.

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Chemical changes are changes by which new substances are formed. These changes cannot be reversed by reversing the conditions.

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The melting of wax is a reversible change that can be brought about by heating. Melted wax is resolidified on cooling.

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The burning of paper is an irreversible change that can be brought about by heating. Burnt paper is converted into ash, a change that can never be reversed. It is a chemical change.

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The two following changes can be brought about by applying pressure:

(a) the breaking of brittle solids
(b) the formation of objects of different shapes from ductile and malleable solids

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Take some sugar in a pan and start heating it slowly. On heating the sugar for some time, it changes its colour to brown. If it is heated for some more time, then a blackish residue of carbon, which is completely different from sugar, is left. This is an irreversible change.

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Exothermic reactions are reactions in which heat is released. Example: The burning of wood.
Endothermic reactions are reactions in which heat is consumed. Example: Mixing of glucose in water.

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Desirable changes are those changes which occur with one's will or desire. Example: Ripening of fruits.

Undesirable changes are those changes which occur without one's will or desire. Example: Souring of milk.

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For making a systematic study of a change, one should observe

(a) any change in the size, shape or colour of the given material
(b) the speed of the change, i.e., how fast or how slow a change is occurring
(c) whether the change is reversible or irreversible
(d) whether the change gives rise to a new substance or not
(e) whether the change is exothermic or endothermic

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The curdling of milk is an irreversible change by which milk is converted to cottage cheese. It can be brought about by mixing a few drops of lemon juice with milk and boiling the mixture for a while. A thick white substance, called cottage cheese, is formed through this process, which is known as the curdling of milk. In this change, a new substance that is different from milk is formed. Hence, it is an irreversible change.

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Physical change Chemical change
(a) The melting of ice (b) The rusting of iron
(e) The evaporation of liquid (c) The cooking of food
(f) The sublimation of iodine (d) The rotting of an egg
(g) The dissolving of a solid (h) The burning of coal
(i) The glowing of a bulb (k) The curdling of milk
(j) The freezing of water (l) Photosynthesis in green plants
(m) The condensation of water vapour (n) The digestion of food

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(d) The burning of kerosene

The burning of kerosene is an irreversible change.

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(c) The condensation of water vapour

The condensation of water vapour is a reversible change.

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(d) Burning

Burning is a change by which new substances are formed.

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(a) The burning of a matchstick

The burning of a matchstick is a chemical change that is completed very fast.



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(b) the air inside the bottle gets heated and expands

The balloon gets inflated because the air inside the bottle gets heated and expands.

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(a) The balloon will get deflated

If the bottle is taken out, then the balloon will get deflated.

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(a) Reversible

A reversible change is taking place in the balloon when the bottle is placed in the hot water and being taken out of it.

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1. When you put some glucose in your mouth, your tongue feels cold, because the dissolving of glucose in saliva is an endothermic change.
2. The slaking of lime is an irreversible change.
3. Many materials expand on being heated.
4. On being heated, a gas expands more than a solid does.
5.

Change Slow/fast Reversible/
irreversible
Any new substances formed
(Yes/no)
Physical/chemical
change
(a) The ripening of a fruit Slow Irreversible Yes Chemical change
(b) The deflating of a cycle tube Fast Reversible No Physical change
(c) The formation of curd from milk Slow Irreversible Yes Chemical change
(d) The formation of black patches on a roti being baked Fast Irreversible Yes Chemical change
(e) The slaking of lime
 
Fast Irreversible Yes Chemical change



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