Question 4 What is freezing?
Question 5 What do you mean by inter-conversion of matter?
Question 6 What is melting or fusion.
Question 7 What does higher melting point indicate ?
Question 8 How does a solid changes into liquid on heating ?
Question 9 How does a liquid changes into vapours on heating ?
Can Matter change Its State
We can change the physical state of matter in two ways:
1)By changing Temperature(heating or cooling)
2)By changing Pressure(increasing or decreasing)
Effect of change of temperature
a) Increasing Temperature
1) Solid to Liquid(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.
For Ex:The ice melts at a temperature of 0°C to form liquid water.So the melting point of ice is 0°C.
Different solids have different melting points.
For Ex:Melting point of iron is 1535°C .Melting point of wax is 63°C
Higher the melting point of solid substance,greater will be the forces of attraction between its particles.
When a solid substance is heated,the heat energy makes its particles vibrate more vigorously.At the melting point,the particles of a solid have sufficient kinetic energy to overcome the strong forces of attraction holding them in fixed positions and break to form small groups of particles.And the solid melts to form a liquid.
2) Liquid to Gas(Boiling or Vaporisation)
The process in which a liquid substance into a gas rapidly on heating is called boiling.
When water changes into steam rapidly on heating,it is called boiling of water.
The temperature at which a liquid boils and changes rapidly into a gas at atmospheric pressure is called boiling point of the liquid.
For Ex:When water is heated to a temperature of 100°C ,it boils rapidly to form a gas called steam,so the boiling point of water is 100°C.
Different liquids have different boiling points.
For Ex:The boiling point of alcohol is 78°C
The boiling point of mercury is 357°C.
The boiling point of a liquid is a measure of the forces of attraction between its particles.Higher the boiling of a liquid,greater will be the forces of attraction between its particles.
When a liquid is heated,the heat energy makes its particle move even faster.At the boiling point the particles of a liquid have sufficient kinetic energy to overcome the forces of attraction holding them together and separate into individual particles.
3)Gas to Liquid(Condensation)
The process of changing a gas or vapours to liquid by cooling is called condensation.
4)Liquid to Solid(Freezing)
The process of changing a liquid into a solid by cooling is called freezing.
Freezing is the reverse of melting.