Physics

Sound

2. Liquid to Gas Change : Boiling (or Vaporisation)

Water normally exists in the liquid state. If we go on heating water, it ultimately starts boiling and changes rapidly into a gas called steam. In this case, the liquid water changes into a gas, so a change of state has taken place. The process in which a liquid substance changes into a gas rapidly on heating,is called boiling. So, when water changes into steam rapidly on heating, it is called boiling of water. A change of state takes place during boiling. The boiling of a liquid takes place at a fixed temperature. The temperature at which a liquid boils and changes rapidly into a gas at atmospheric pressure, is called boiling point of the liquid. For example, when water is heated to a temperature of 100°C, it boils rapidly to form a gas called steam, so the boiling point of water is 100°C (hundred degrees Celsius). At boiling point, water changes its state from liquid to gas (or vapour).
Different liquids have different boiling points.For example,the boiling point of alcohol is 78°C,whereas the boiling point of mercury is 357°C. The boiling point of a liquid is a measure of the force of attraction between its particles. Higher the boiling point of a liquid, greater will be the force of attraction between its particles.For example, the boiling point of mercury is very high (357°C) which tells us that the force of attraction between the particles of mercury is very strong. We will now describe how a liquid changes into a gas on heating.
When a liquid is heated, it changes its physical state and becomes a gas. This happens as follows : When a liquid is heated, the heat energy makes its particles move even faster. At the boiling point theparticles of a liquid have sufficient kinetic energy to overcome the forces of attraction holding them together and separate into individual particles. And the liquid boils to form a gas.

Notes

Sound - Notes

1. 3. Humidity of Air