States of Matter

The physical States of Matter

The universe is made of Matter. The tiniest of particles, Atoms, combine to form molecules, which are the building blocks for all forms of matter.

Matter exists primarily in three physical states– Solid, Liquid, and Gas. (See also: Matter and its Structure)

Gases have the following properties –

• No definite shape or volume, such as hydrogen or helium gas
• Exert Pressure and Expand in all directions to fill the closed container which they are held in
• Can be compressed into a very small space
• Cannot be confined to space in an open container

How Matter Changes State

How does a mercury thermometer, which displays the temperature, work? The mercury inside the thermometer is sensitive to temperature – it expands when the temperature rises and contracts when it falls. This tells us how hot or cold it is around us. The thermometer is an example of the effect of heat on matter.

The molecules of matter are in constant motion. When the matter is heated, the molecules start to vibrate even faster. As a result, the space between them increases and the matter expands. The reverse happens when the matter is cooled. The extent of heating or cooling applied to matter changes the state of that matter.

A solid when heated past its Melting Point will melt into liquid.

A liquid when heated past its Boiling Point will vaporize that matter into gas.

A gas when cooled below its Condensation Point will form liquid from that matter.

A liquid when cooled below its Freezing Point will form solid from that matter.

The chemical properties of the matter remain unchanged when they change from one state to another – only the physical properties change. Let us see with an example –

How Water Changes State

Water exists in three states in nature. It is abundantly seen in its liquid form.

Water has a boiling point of 100^o Celsius (212^oF). When water is heated past its boiling point, it vaporizes to form water vapor, a gas.

Water has a freezing point of 0^o Celsius (32^oF). When water is cooled below its freezing point it forms ice, a solid.

In all three states, the chemical properties of water remain the same – it is still just water – though its physical properties have changed.

Check Point

1. Which of the following is NOT a property of a solid?
   1. Has a form and shape
   2. Flows easily
   3. Is ductile and malleable
   4. Does not undergo a shape change easily
2. Which of the following is NOT a property of a gas?
   1. No definite shape or volume
   2. Exert pressure and expand in all directions
   3. Cannot be easily compressed
   4. Cannot be confined in an open container
3. A solid which is heated past its melting point becomes ______.
4. A gas which is cooled below its condensation point becomes ______.
5. A liquid which is cooled below its freezing point becomes _______.

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