Grade 8 Science Unit 8 Sri Lankan Science Textbook with additional explanations, examples #science

# Grade 8 Science – Unit 8 # Changes in Matter

Based mainly on the Grade 8 Sri Lankan Science Textbook with additional explanations, examples, experiments, daily-life applications, and revision support.

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# Unit Overview

In our day-to-day life, matter changes continuously. Ice melts, water boils, paper burns, iron rusts, candles burn, fruits ripen, and metals tarnish. Some of these changes only affect the appearance or state of matter, while others create completely new substances.

This unit helps students understand:

* Physical changes
* Chemical changes
* Changes of state
* Combustion
* Law of conservation of mass
* Tarnishing and rusting
* Neutralisation reactions

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# 8.1 Physical Changes and Chemical Changes

## What is a Physical Change?

A physical change is a change in which:

* The composition of matter does NOT change.
* No new substance is formed.
* Only the shape, size, or state changes.

## Examples of Physical Changes

* Tearing paper
* Melting ice
* Melting wax
* Breaking glass
* Dissolving salt in water
* Boiling water
* Freezing water
* Sublimation of iodine

## Important Features of Physical Changes

* No new substances are formed.
* Usually reversible.
* Chemical composition remains the same.
* Only physical properties change.

## Example from the Textbook

When paper is torn into pieces:

* It still remains paper.
* The composition does not change.
* Therefore, it is a physical change.

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## What is a Chemical Change?

A chemical change is a change in which:

* The composition of matter changes.
* One or more new substances are formed.

## Examples of Chemical Changes

* Burning paper
* Rusting iron
* Burning magnesium ribbon
* Cooking food
* Ripening fruits
* Digestion of food
* Tarnishing metals
* Combustion of fuels

## Important Features of Chemical Changes

* New substances are formed.
* Usually irreversible.
* Chemical composition changes.
* Heat, light, sound, gases, or precipitates may form.

## Example from the Textbook

When paper burns:

* Ash and smoke are produced.

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