States of matter | Grade 4 Science | Learning Concepts | Orchids
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States of Matter

Concept: Changes in the States of Matter

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.

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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.

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

1. 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.

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2. 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.
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Example:

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

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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.
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Example:

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