Know how many states of matter are there.
Get an idea about what are the states of matter.
Name the three states of matter.
Analyse the solid state of matter, the liquid state of matter, gas state of matter.
Understand what is melting and what is freezing.
Know the difference between evaporation and condensation.

Each concept is explained to class 4 students using descriptions, illustrations, and concept maps. After you go through a concept, assess your learning by solving the two printable worksheets given at the end of the page.

Download the worksheets and check your answers with the worksheet solutions for the concept of the Interconversion of States of Matter provided in PDF format.

There are three main states of matter—solids, liquids, and gases. Matter can change from one state to another as a solid can turn into a liquid or a gas and vice versa. This phenomenon is called the change of state of matter.

Example: The best way to demonstrate the conversion of states of matter is by taking the example of water.

Water is a liquid, which turns into a gas (water vapour) on heating, and freezes into a solid (ice) by lowering the temperature. The reverse processes are also a common phenomenon.

Let us now look at the different processes involved in the change of states of matter.

1. What Is Melting?

At a specific temperature and pressure, a solid gets converted into its liquid state; it is called melting.
Melting occurs when heat is applied.
Due to the increase in temperature, the intermolecular force of attraction between the molecules of the solid weakens, and that is why the solid changes into a liquid.

Example: If we take out an ice cube or a cube of butter from the refrigerator and keep it outside for a few minutes, the ice cube melts into water, and the butter also melts into a liquid. Ice creams melt into a liquid when kept outside.

2. What Is Freezing?

Freezing is when a liquid changes into a solid at a specific temperature and pressure.
As the temperature decreases, the speed of the liquid molecules also decreases, and as a result, the movement of liquid molecules gets restricted, and the liquid transforms into a solid.

Examples:

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When we keep water inside the freezer, it turns into ice, which is a solid.
Lava hardens into solid rocks.

3. Evaporation:

At a specific temperature and pressure, the conversion of liquid into a gas is called evaporation.
Evaporation is also called vapourisation.
Due to the application of heat, the intermolecular force of attraction among the liquid molecules weakens, and gradually the molecules become free to move randomly.
This is how the liquid state changes into a gaseous state.

Example:

When we boil water, it gets converted into steam.
Due to evaporation, rivers, ponds, and lakes become dry up during the summers.

4. Condensation:

The conversion of the gaseous state of matter into its liquid form at a specific temperature and pressure is called condensation.
At a low temperature, the gas molecules lose their speed, get closer, and transform into a liquid.

Example: The following phenomena occur as a result of condensation.

Formation of droplets outside a glass tumbler containing cold water.
Fogging a mirror by exhalation of breath.
Morning dew on the grass.
Occurrence of rainfall.

Melting point	The temperature at which a solid changes into a liquid state by absorbing heat is called the melting point.
Freezing point	The temperature at which a liquid changes into a solid by releasing heat is called the freezing point.
Boiling point	The temperature at which a liquid changes into a gas by absorbing heat is called the boiling point.
Condensation point	The temperature at which a gas changes into a liquid by releasing heat is called the condensation point.

Factors Affecting the Changes in the States of Matter:

1. Temperature:

At a high temperature, the molecules of different forms of matter start to move faster.
At a low temperature, the molecules of different forms of matter move slower.

2. Pressure:

At high pressure, the molecules of any matter remain closely packed.
At low pressure, the molecules of the matter remain loosely packed.

New Words:

Molecules: These are the smallest identifiable unit of a substance with all the properties of that substance.

Intermolecular force: The force acting among the molecules of a substance.

Pressure: The physical force exerted per unit area of an object.

Temperature: The degree of hotness and coldness of a body. It can be measured by a thermometer.

Did You Know?

A process of turning a solid into a liquid is dissolving. For example, sugar dissolves into a glass of water on stirring.
The conversion of a solid directly into a gas without going through the liquid state is called sublimation.

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