Kinetic theory can be used to explain what happens when a substance changes from one state to another, for example when ice melted to become water.
             The main points of the kinetic theory are:
             • All matter is made of particles. There are particles in all materials-glass, wood, paper.
             • The individual particles are very small.
             • The particles of different substances have different sizes. Particle of elements such as aluminium iron and oxygen are very small. Particles of compound like sugar are larger. Particles of some complex compound s such as rubber proteins are thousand times bigger.
             • The particles in all substances are continually moving. Small particles move faster that heavier particles at the same temperature.
             • As temperature rises, the particles get hotter. They have more energy and move around and faster.
             • In a solid the particles are very close with strong forces between them. Solid particles can only vibrate about fixed positions. This explains why solids have a fixed shape and a fixed volume.
             • In a liquid the particles are a little further apart. The forces between the particles are not as strong. Liquid particles can move around each other. So liquids can change their shape but they keep a fixed volume.
             • I n a gas the particles are much further apart. There are no forces to hold the particles together. The particles rush around in all direction in all the space that they can find. So gases change their shape and their volume depending on their container.
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