The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:
Every second, everything around us is continually changing. From our hair and nails growing to our lungs expanding and contracting while breathing to the movement of the moon. Our environment is constantly changing. Some of these changes are temporary, meaning they can change back to their original form, while some are permanent, meaning they can’t go back to their original state. A few of these changes are not even noticeable. Let’s understand what these changes really mean.
Any difference in the shape or size of an object is referred to as a change. Some changes can always be reversed, while some can’t. Based on this, you can classify changes into two broad categories (1) Reversible and (2) Irreversible changes-
(1) Reversible changes are the type of changes that can be undone or reversed.
(2) Irreversible changes are the type of changes that cannot be undone or reversed.
Apart from reversible and irreversible changes, there is another way to classify changes – Physical and Chemical changes.
(1) Physical changes affect the physical properties of a substance, but the chemical properties remain the same. For example, boiling water, freezing water, melting wax, etc.
(2) Chemical changes affect both the chemical and physical properties of a substance. For example, digestion of food, burning of coal or paper.
Expansion and contraction
Burning or combustion is an irreversible process where a substance burns to produce a new substance. A good example of this is coal burning; burning coal produces fly ash and various other gasses like CO2, NOx, SO2, and particulate matter that causes pollution.
Many substances you see around you are not in their pure form. They are a mixture of two or maybe more than two substances. You can separate different substances of a mixture to obtain individual components that make up the mixture. A good example is water sedimentation, where you separate impurities like dirt and mud from water to obtain pure water.
It is fascinating to know that every object around you is undergoing some change at all times. Many changes are based purely on heat, and the level and speed of change depend on the heat supplied. Supply enough heat, and you can change the state of any object around you. From simple substances like water to complex ones like coal, when changed, produces results different from a substance like water.
Rotation of earth, rise, and fall of temperature, melting of ice to become water are examples of changes around us.
Boiling water, folding paper, and cutting wood.
Changes occur around us all the time; sometimes, these changes happen instantaneously and sometimes slowly. Changes can be classified into 4 types-
Physical changes: They only change the physical attributes of the material and not the chemical composition. For example, the melting of ice.
Chemical changes: They change the physical and chemical composition of the material. For example, burning coal.
Reversible changes: These changes can be reversed. For example, water can be frozen once again when obtained from melting ice.
Irreversible changes: They cannot be reversed. For example, if you burn paper, you cannot make paper from ashes.
Rotting of food, rotation of the earth, and movement of the moon.
The two types of changes are reversible and irreversible changes. Reversible changes can be undone or reversed, e.g., melting of ice. Irreversible changes can’t be undone or reversed, e.g., burning of coal.
Physical changes are- melting of ice, cutting paper, folding clothes.
Chemical changes are- digestion of food, ripening of a mango, burning coal.
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