PHYSICAL CHEMISTRY - Properties of Liquids

The intermolecular distance in liquid molecular are not as large as in the care of gas. Thus the intermolecular forces of attraction in liquid molecules are stronger as compared to that of gas molecules thus the liquid does not have definite volume. Hence liquid do not obey gas laws. However liquid posses certain characteric phusical properties. These physical properties are used as tool to decide the chemical constitution of each liquid some important physical properties of liquids are :-

1. Vapour Pressure
2. Surface Tension
3. Viscosity
4. Refractive Index
5. Optical Activity
6. Dipole Moment

<b>1. Vapour Pressure :-</b> Molecules of liquid, like those of gas, exhibit a distribution of energies. The molecules that have sufficient energy to overcome intermolecular attraction can escapeform the bulk into the gas phase provided they are close to the surface. This happens during evaporation. Since the average kinetic energies of molecules in vapour state is more than that in liquid state, the temprature of the liquid falls on evaporation . The rate of evaporation of a liquid depends upon the temprature of the liquid and attractive forces in the liquid and surface area and pressure above the liquid.

<b>2. Surface Tension :-</b> The strong intermolecular forces present in liquids give another important known as the surface tension. This property may be explained by refrence. Mathematically, surface tension may be defined as the forces in dynes acting at right angle to the surface of the liquid along one centimeter length of the surface.

<b>3. Viscosity :-</b> The flow is a characteristic property of liquids. They do not flow with the same speed. Some liquids like water, ether etc. Flow fast while some other liquids like sulphuric acidcastor oil, glycerol etc flow very slow. This showed that every liquid has some internal resistance to flow. The resistance to flow exhibited by liquid is known as viscosity. Becouse of this property some liquids flow slowly than others.