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.
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.