Class 7 Science Made Simple: An Explanation of Physical and Chemical Changes

We see many things change around us every day. Ice melts into water, milk turns sour, paper burns, and water boils. These changes are common in our daily life. But have you ever thought about why these things happen or how they are different from each other?

In Class 7 Science, one of the interesting and important topics is physical and chemical changes. This topic helps us understand what really happens when something changes its form, state, or nature. In this article, we will explain everything in a simple and easy way that any Class 7 student can understand.

What is a Change?

A change means when something becomes different from what it was before. Changes happen in size, shape, color, state, or even substance. Some changes are small and temporary, while others are big and permanent.

For example:

Ice melting is a temporary change.
Burning of wood is a permanent change.

Scientists divide changes mainly into two types:

Physical changes
Chemical changes

What is a Physical Change?

A physical change is when the form or appearance of a substance changes, but the substance itself stays the same. This means no new material is created. The substance may change its shape, size, or state (solid, liquid, gas), but its nature remains unchanged.

Main Features of Physical Changes:

No new substance is formed
The original substance remains the same
Usually reversible (can be changed back)
Only physical properties like shape or state change

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Simple Examples of Physical Change:

Ice melting into water
Water turning into steam
Cutting vegetables
Tearing a sheet of paper
Mixing salt in water

These are all physical changes because the materials remain the same even after the change.

What is a Chemical Change?

A chemical change is when a new substance is formed that has different properties from the original one. These changes are usually permanent and cannot be reversed easily.

Main Features of Chemical Changes:

A completely new substance is formed
The original material cannot be easily recovered
Often irreversible
May produce heat, light, color change, or gas
Changes the chemical structure of the substance

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Simple Examples of Chemical Change:

Burning of paper or wood
Rusting of iron
Cooking food
Milk turning sour
Fireworks bursting

These changes cannot be undone easily and result in new substances, which is why they are called chemical changes.

Comparison: Physical vs Chemical Changes

To understand physical and chemical changes better, let’s compare them side by side:

Point of Difference	Physical Change	Chemical Change
New Substance Formed?	No	Yes
Reversible?	Mostly reversible	Mostly irreversible
Change in State or Form?	Yes	Yes
Change in Chemical Nature?	No	Yes
Examples	Melting ice, folding paper	Burning wood, rusting iron

This table will help you remember the differences easily during your Class 7 exams.

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How to Know if a Change is Physical?

Here are signs that tell you a change is physical:

Only the shape, size, or state changes
No new material is formed
You can get back the original substance
No color or smell change
No gas or heat is released

Example: Freezing juice into ice cubes. The juice just becomes solid. You can melt it back. So, it’s a physical change.

How to Know if a Change is Chemical?

Here are some clues that a chemical change has taken place:

A new substance is formed
There’s a change in color or smell
Bubbles or gas is released
Heat or light is given off
Cannot be reversed easily

Example: Burning a candle. The wax melts (physical), but it also burns and produces new gases and ash (chemical).

Real-Life Examples of Physical and Chemical Changes

Physical Changes in Daily Life:

Water boiling to form steam
Glass breaking
Ice melting in summer
Sugar dissolving in water
Paper folding into a boat

Chemical Changes in Daily Life:

Bread turning brown when toasted
Apple slices turning brown in air
Iron rusting in rain
Cooking vegetables
Soap reacting with acid

Understanding these real-life examples helps you relate this science topic to what you see around you.

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Physical and Chemical Changes in Nature

Nature also shows us both physical and chemical changes.

Examples of Physical Changes in Nature:

Snow melting into water
Water forming clouds through evaporation
Rocks breaking into sand by wind or water

Examples of Chemical Changes in Nature:

Dead leaves rotting and turning into compost
Lightning changing gases in the air
Plant leaves turning yellow in autumn
Fruits ripening over time

These natural processes are beautiful examples of how physical and chemical changes keep the environment in balance.

Can a Change Be Both Physical and Chemical?

Yes, sometimes a single event can include both types of changes.

Example 1: Burning a Candle

Physical change: Wax melts
Chemical change: Wax burns and produces new substances

Example 2: Cooking Rice

Physical change: Water boils
Chemical change: Raw rice changes into soft cooked rice

So, both physical and chemical changes can happen together in one process.

Simple Experiments You Can Try at Home

Experiment 1: Ice Melting (Physical Change)

Take some ice cubes in a bowl.
Watch them melt into water.
This is a physical change because you can freeze the water again.

Experiment 2: Vinegar and Baking Soda (Chemical Change)

Mix a spoon of baking soda with vinegar in a glass.
Bubbles will appear and fizzing sound will be heard.
This is a chemical change because gas is produced, and a new substance is formed.

These fun and easy activities can help Class 7 students see physical and chemical changes in action.

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Why Are These Changes Important?

Both physical and chemical changes are very important in science and everyday life.

Importance of Physical Changes:

Used in industries like paper making and water purification
Helps us to store and transport materials
Makes life more convenient (like melting wax or freezing food)

Importance of Chemical Changes:

Used in cooking and digestion
Helps in making medicines and cleaning products
Used in construction and farming
Helps in producing energy from fuels

So, learning about these changes is useful in real life and builds strong science knowledge for the future.

Conclusion

We hope you now clearly understand what physical and chemical changes are. These changes happen all around us—in homes, in schools, in nature, and even inside our bodies.

To remember:

A physical change affects only the appearance or state.
A chemical change creates a new material with new properties.
Some changes may include both physical and chemical changes.
Observing changes can help us understand the world better.

If you keep watching closely, you will find many such examples every day. Science becomes fun when you start connecting what you learn in class with real life.