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Class 6 Science Chapter 6 Changes Around Us, Reversible Change, Irreversible Change
Changes Around Us
Introduction
- Everything around us in the environment undergoes a change after a certain period.
- Some changes are temporary while some are permanent.
- New leaves come out with the old ones turning yellow and falling down the trees.
Two Types of Changes
Reversible Change
- Changes that can be reversed are known as reversible changes.
- Actions may be reversed or the conditions may get changed.
- Some of the examples are freezing of water, melting of ice, folding of paper, etc.
Irreversible Change
- Those changes that cannot be reversed are known as irreversible changes.
- Some of the examples are rusting of iron, cooking, burning of paper, etc.
Two Major Types of Changes That Substances Undergo
Physical Change
- There is no change in the composition of the matter.
- No new substance is formed after the change.
- These changes are usually reversible.
- Some of the examples are Freezing water to make ice cubes, Boiling water evaporating, Hot shower water turning to steam, melting of wax, Breaking Glass, Chopping wood, etc.
Chemical Change
- New substance is formed after the change.
- These changes are often reversible.
- These changes cannot be reversed by simple physical means.
- These changes have a direct impact on the chemical bonds and molecular composition of the material.
- Some of the examples are rusting of iron, electroplating, metabolism, Chemical Battery, Fireworks, etc.
Causes of Change
Force
- Certain things may undergo change due to force.
- Some of the examples are movement of vehicles, the balloon gets in flattened on blowing air into it, hammering a piece of gold, and making designs out of it, etc.
Temperature
- On application of thermal energy to a substance its temperature increases which changes its state from solid to liquid (melting) , liquid to gas (vaporization) , or solid to gas (sublimation) .
- One of the examples is that of an ice which melts and turns into water.
Ways to Bring About Changes in Substances
Mixing Two Substances Together
- One of the examples is that of adding a small amount of curd to the warm milk.
- This converts warm milk into curd which is an irreversible change.
Expansion and Contraction
One of the examples is that of the jammed metal lid of a jam jar that can be opened by heating.
Other Changes
Based on Speed
Fast Changes
For example, switching off the fan.
Slow Changes
For example, growth of a child into an adult.
Based on Energy
- Heat gets absorbed in the process i.e.. , Endothermic.
For e. g. , Condensation of water.
- Heat energy is given out in the process i.e.. , Exothermic.
For e. g. , Photosynthesis.
Based on Time Interval
Periodic Changes
- For example, change in phases of moon.
- These changes occur repeatedly after regular intervals of time.
Non-Periodic Changes
- For example, natural disasters.
- These changes that donΥt repeat themselves at regular intervals of time.