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.
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.
- 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.
- 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.
- When we keep water inside the freezer, it turns into ice, which is a solid.
- Lava hardens into solid rocks.
- 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.
- When we boil water, it gets converted into steam.
- Due to evaporation, rivers, ponds, and lakes become dry up during the summers.
- 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:
- 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.
- At high pressure, the molecules of any matter remain closely packed.
- At low pressure, the molecules of the matter remain loosely packed.
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.