THE LIQUID STATE

The liquid state

A liquid state is intermediate between the gas and the solid.

Liquids have no definite shape, but definite volume.

Liquids have higher density than gases, much less compressible than gases. They show diffusion much lower than those of gases.

Vapour pressure →

It is defined as pressure exerted by vapours present above the liquid in equilibrium with the liquid at that temperature at any temperature.

Cooling is caused by evaporation, because during evaporation more energetic molecules leave the surface of liquid leaving behind low energy molecules, so temperature of liquid falls and cooling takes place.

If any liquid has higher vapour pressure, then it means, the liquid has weaker inter molecular forces of attraction

Lower the vapour pressure of a liquid, greater is inter molecular force of attraction

→ Effect of temperature → With the increase of temperature vapour pressure of a liquid increases.

Boiling point → It is defined as a temperature at which vapour pressure of a liquid becomes equal to atmospheric pressure when external pressure is normal atmospheric pressure i.e. 760 mm then boiling

point is normal boiling point. When external Pressure is 1 bar, then boiling point is standard boiling point and normal boiling point of water is 100^°C

Standard boiling point of water is 99.6^°C

→ Greater the external pressure, Greater is boiling point so inside the pressure cooker, pressure is very high so boiling point of water increases and vegetables take time to be cooked.

→ At hilly areas, pressure of atmosphere is low boiling pt. of water will also be low and vegetables take more time to be cooked. So use of pressure cooker is essential for cooking food.