Matter In Our Surrounding

We can change the physical state of matter in two ways:

• By changing the temperature, and
• By changing the pressure

EFFECT OF CHANGE OF TEMPERATURE

Solid to Liquid Change – Melting:

• The process in which a solid substance changes into a liquid on heating is called melting or fusion.
• The temperature, at which a solid substance melts and changes into a liquid at atmospheric pressure, is called melting point of the substance.
• The melting point of a solid is a measure of the force of attraction between its particles.
• On increasing the temperature of solids, the kinetic energy of particles increases which leads to the vibration of particles with greater speed.
• This overcomes the forces of attraction between the particles allowing the particles to leave their fixed positions and start moving more freely.
• This results to a stage where the solid substance changes into a liquid on heating and is called melting (or fusion).

Liquid to Gas Change – Boiling or Vaporisation:

• On heating of liquid, a change in physical state is observed, where the liquid substance changes into a gas. This process is called as boiling.
• The temperature, at which a liquid boils and changes rapidly into a gaseous state at atmospheric pressure, is called boiling point of the liquid.

Gas to Liquid Change – Condensation:

• The process of changing a gas (or vapour) to a liquid by cooling, is called condensation.

Liquid to Solid Change – Freezing:

• The process of changing a liquid into a solid by cooling is called freezing.