Change of state


•      Matter can change from one state to another.

       For example, water (liquid) can be changed into steam which is a gas, and ice (solid) can melt and changes into water (liquid).

•      These changes depend upon the movement of the tiny particles present in it.



•      The process of conversion of liquid into gaseous state is called evaporation.

•      This happens because on heating; the particles of water start moving (or vibrating) faster.

•      Finally, they break free from their existing arrangement and escape into the air.

•      They change into gas, where the particles can move much more freely.

•      Heating a substance makes its particles move or vibrate faster.



•      The process of conversion of gaseous to liquid state is called condensation.

•      When the freely flowing particles of steam touch a cold surface, it condenses.

•      Cooling a substance slows down the movement of its particles.

•      The particles thus become less free to move and change from gas to liquid (water).



•      A change from a solid to liquid state is termed as melting.


For example:


Figure 5- Ice melts when kept at room temperature

•      If we keep the ice cubes at room temperature, after some time we’ll observe that it has converted into water.

•      The water particles in solid ice are rigidly packed to give it a fixed shape.

•      When ice is taken out of the refrigerator, it melts gradually.

•      This is because in a warm place, the water particles in ice start vibrating faster, and finally break away from the rigid pattern.

•      They become loosely packed as in a liquid and form water.



•      A change from a liquid to solid state is termed as freezing.

•      During this process (liquid to solid), the molecules get closer together.

       For example: if we keep the water in a refrigerator, after some time we will observe that it has changed into ice.

•      When water is cooled, its particles start slowing down and pack themselves into a rigid shape, thus forming solid ice.

•      Change of state not only takes place in water but in other substances also.

•      Like – mercury is liquid at room temperature but it converts into solid state (at -37 to 39 degrees Celsius) when kept in frozen condition.