Any matter around us can be in the three forms : solid ,liquid and gas called states of matter. Depending upon the temperature, pressure and transfer of heat, matter is converted from one state to another and is known as change of state in matter. There are different such processes in the change of state in matter.
For example:
Water molecules are in liquid state at normal temperature. When water is heated to `100^@C`, it becomes steam or vapour which is a gaseous state of matter. The process by which a liquid is converted to vapour by absorbing heat is called boiling or vaporization.
The temperature at which a liquid changes its state to gas is called boiling point.
On reducing the temperature of the steam it becomes water again. The process by which a vapour is converted to liquid by releasing heat is called condensation. On reducing the temperature of water further to `0^@C`, it becomes ice which is a solid state of water.
The process by which a liquid is converted to solid by releasing heat is called freezing. The temperature by which a liquid changes its state to solid is called freezing point. Ice on heating, becomes water again by absorbing heat, a process known as melting .
Dry ice changes directly to gaseous state without becoming liquid. This process is called sublimation.
Thus, water changes its state when there is a change in temperature.
