CBSE Class 9 Answered

Effect of change of Temp:

On increasing the temperature, the kinetic energy of the particles increases.Particles with increased kinetic energy start vibrating with greater speed.The energy supplied by heat overcomes the forces of attraction between the particles as a result particles leave their fixed positions and start moving more freely.A stage is reached when the solid melts and is converted to a liquid. The temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.A gaseous state exists when molecules have absorbed so much heat energy due to increased temperatures that they are free to move around one another at high speeds

Effect of change of pressure on matter:

On lowering temperatur eand increasing the pressure gases can be changed into liquids while some solids can be changed into gases on decreasing the pressure. As there is lots of space available between the particles of a gas so upon applying high pressure particles come close to each other which upon cooling gets liquified